path: root/docs/design/2026-07-10-net-bt-failure-taxonomy.org

#+TITLE: Linux Network and Bluetooth Failure Taxonomy — for the net and bt doctors
#+AUTHOR: Craig Jennings
#+DATE: 2026-07-10

* Purpose

A catalogue of real, user-reported ways Linux networking (WiFi/ethernet/DNS/egress) and Bluetooth fail, grounded in forum and issue-tracker reports. Built to feed the net-panel and bt-panel doctors the same way the audio taxonomy fed the audio doctor: each entry is triaged into a remedy class — AUTO (the doctor applies a user-scope reversible fix), PRIV (needs root; runs where passwordless sudo exists), REBOOT-TAIL (a privileged fix that only takes hold after a reboot), or GUIDE (nothing to run — a physical action, a config decision, or an upstream/venue problem). This mirrors [[file:2026-07-10-audio-failure-taxonomy.org][the audio taxonomy]] and reuses its four-class privilege model.

The net and bt doctors already exist (=~/.dotfiles= =net/= and =bluetooth/=). This taxonomy grounds their *expansion* — widening the diagnosis space and hardening the verdict/remedy structure — the way the audio input-side spec grew from the audio taxonomy. It fed two DRAFT specs: [[file:../specs/2026-07-11-net-doctor-expansion-spec.org][the net doctor expansion]] and [[file:../specs/2026-07-11-bt-doctor-expansion-spec.org][the bt doctor expansion]].

** Method

Built 2026-07-10 from a blind, by-layer parallel research fan-out — the same first-sweep method as the audio taxonomy. Eleven agents (six network, five bluetooth), each scoped to one layer and blind to any cluster structure, drew real failure reports from Arch BBS/wiki, kernel bugzilla/launchpad/gitlab, distro forums, and upstream issue trackers, weighted toward 2023-2026 and the Arch / NetworkManager / systemd-resolved / bluez stack. Each entry names the layer, the user-reported symptom, the root cause, the known fix (with the concrete command where one exists), the privilege/reboot signal, and a source.

The =(privilege signal)= after each title is the first triage cue: =no= = user-scope, no reboot; =yes= = needs root; =both= = root AND a reboot; =physical= = a hardware/physical/BIOS action. A =no= is an AUTO candidate; =both= or =physical= can only ever be REBOOT-TAIL or GUIDE.

A saturation resample (the audio taxonomy's blind-different-axis check) is a later pass, noted at the end.

* Network failure modes

Six layers, mirroring the net doctor's probe ladder (link → IP/DHCP → gateway/route → DNS → egress) plus the NetworkManager control plane that sits beside all of them. ~98 raw entries from the sweep; the obvious cross-layer duplicates (VPN route capture, PMTUD blackhole, broken-IPv6/happy-eyeballs, unmanaged device, dhcpcd-vs-NM, wifi powersave, connectivity-check false negative, MAC randomization, iwd/wpa_supplicant backend) are merged inline and cross-noted, leaving ~74 distinct root causes.

** Link / radio / driver / firmware / rfkill

- Missing iwlwifi firmware for a very recent Intel card (both). No wifi interface in =ip link=; dmesg "Direct firmware load for iwlwifi-… failed with error -2". The installed linux-firmware predates the card's blob. Fix: update/install linux-firmware (or linux-firmware-git), reboot. [[https://bbs.archlinux.org/viewtopic.php?id=193570][arch 193570]]
- iwlwifi firmware-load regression after a kernel update (both). Wifi vanished right after an upgrade; dmesg shows iwlwifi failing to load firmware it loaded before. A kernel-side change broke firmware negotiation for that module. Fix: boot linux-lts or update to the fixed kernel, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=304848][arch 304848]]
- Realtek rtw89 in-tree module shadowed by an AUR DKMS driver (both). RTL8852BE wifi disappeared after an update; two conflicting modules present. A stale 8852be/rtw89-dkms-git overrides the in-tree rtw89_8852be. Fix: remove the AUR DKMS package, ensure linux-firmware is current, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=286109][arch 286109]]
- MediaTek mt7921e broken by a linux-firmware update (both). Wifi worked, then a pacman upgrade killed it; firmware load timeout / "hardware init failed" for WIFI_RAM_CODE_MT7961. A regression in the packaged blob fails to init the chip. Fix: downgrade/pin linux-firmware-mediatek to the last-good version, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=308360][arch 308360]]
- Broadcom BCM4360 needs the proprietary wl driver (both). "No wifi adapter"; lspci shows BCM4360 but no wlan interface. The open brcm/b43/bcma drivers claim it but can't drive it. Fix: install broadcom-wl-dkms, blacklist b43/bcma/brcmsmac/brcmfmac/ssb, rebuild initramfs, reboot. [[https://wiki.archlinux.org/title/Broadcom_wireless][archwiki broadcom]]
- broadcom-wl (non-DKMS) breaks after a kernel upgrade (both). Wifi gone after a kernel bump; wl won't load against the new kernel. The prebuilt module isn't rebuilt automatically. Fix: switch to broadcom-wl-dkms, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=305252][arch 305252]]
- USB wifi dongle needs an out-of-tree DKMS driver (both). An RTL8811AU/8812AU/8821AU dongle enumerates in lsusb but no wlan interface appears. No in-tree driver binds it. Fix: install the matching DKMS package with kernel headers, reboot. [[https://aur.archlinux.org/packages/rtl8812au-dkms-git][aur rtl8812au]]
- Wifi soft-blocked by rfkill (no). =rfkill list= reports "Soft blocked: yes"; the radio is off. Software (a prior toggle, a hotkey, NM state) set the soft block. Fix: =rfkill unblock wifi= (or =nmcli radio wifi on=). [[https://bbs.archlinux.org/viewtopic.php?id=236715][arch 236715]]
- Wifi hard-blocked by a physical switch / airplane / BIOS (physical). "Hard blocked: yes"; no software clears it. A kill-switch, Fn toggle, or BIOS setting physically disables the radio. Fix: flip the physical/Fn switch or enable the radio in BIOS. [[https://bbs.archlinux.org/viewtopic.php?id=207376][arch 207376]]
- rfkill stuck hard-blocked after suspend from competing WMI modules (both). Wifi comes back hard-blocked after resume and unblock won't clear it. Two vendor WMI modules (acer_wmi + hp_wmi) both claim the switch and wedge it. Fix: blacklist the wrong WMI module, rebuild initramfs, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=236657][arch 236657]]
- iwlwifi crashloops on resume, needs a module reload (yes). Wifi dead after suspend; dmesg shows microcode errors / firmware crashloop until the driver reloads. Firmware state isn't restored across resume. Fix: =modprobe -r iwlmvm iwlwifi && modprobe iwlwifi= (or a system-sleep hook). [[https://bbs.archlinux.org/viewtopic.php?id=293404][arch 293404]]
- ath11k (QCA6390/QCNFA765) firmware crash, dead until reload (yes). Wifi drops after resume or at random; dmesg "ath11k_pci … firmware crashed: MHI_CB_SYS_ERROR". The card's firmware faults and doesn't recover. Fix: =modprobe -r ath11k_pci && modprobe ath11k_pci=. [[https://bbs.archlinux.org/viewtopic.php?id=310363][arch 310363]]
- WiFi powersave drops the connection (yes; merges the auth-layer and NM-layer duplicates). Wifi connects then stalls/disconnects, worse on battery. Aggressive power management (driver =power_save= and/or NM =wifi.powersave=3=) breaks association with some APs. Fix: =iw dev wlan0 set power_save off= now; persist via NM =[connection] wifi.powersave=2= drop-in and/or =options iwlwifi power_save=0= in modprobe.d. [[https://bbs.archlinux.org/viewtopic.php?id=171342][arch 171342]]
- USB wifi dongle killed by USB autosuspend (yes). A working dongle drops out after idle and returns on replug; =power/control= reads "auto". Autosuspend powers the device down mid-use. Fix: a udev rule pinning =power/control=on= (or disable USB autosuspend in TLP). [[https://bbs.archlinux.org/viewtopic.php?id=184823][arch 184823]]
- RTL8125 ethernet flips from r8125 to in-tree r8169 after a kernel update (both). Wired network dies after an upgrade; the NIC binds r8169 and shows NO-CARRIER. A kernel update overrode the AUR r8125 module. Fix: blacklist r8169, install/force r8125-dkms, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=262120][arch 262120]]
- RTL8125 link downshifts / won't negotiate full speed (yes). The 2.5GbE NIC links but only at 1Gbps/100Mbps; ethtool shows the reduced speed. EEE / Giga-Lite negotiation downshifts the PHY. Fix: =ethtool --set-eee <if> eee off= (or force speed via =ethtool -s=), or swap cable/port. [[https://bbs.archlinux.org/viewtopic.php?id=264742][arch 264742]]
- Ethernet NO-CARRIER from an unplugged/faulty cable or dead switch port (physical). Interface UP but NO-CARRIER, no IP ever assigned. No link partner: cable unseated/broken or switch port down. Fix: reseat/replace the cable, try another port — no software repair until carrier returns. [[https://bbs.archlinux.org/viewtopic.php?id=268745][arch 268745]]
- Adapter present but left "unmanaged" by NetworkManager (no/yes; merges the NM-layer duplicate). =nmcli device= lists the device "unmanaged". Another daemon (iwd, systemd-networkd) owns it, or an =unmanaged-devices= rule / =NM_MANAGED=no= excludes it. Fix: =nmcli device set <dev> managed yes= (AUTO); remove the config rule or disable the rival manager to persist (PRIV). [[https://bbs.archlinux.org/viewtopic.php?id=291445][arch 291445]]

** WiFi association / authentication

- Wrong PSK, NM state 120 / secrets required (no; TERMINAL). "Secrets were required, but not provided"; journal "4-Way Handshake failed — pre-shared key may be incorrect". NM stored the wrong key — no repair fixes it; the user must re-enter. Fix: =nmcli con modify <name> wifi-sec.psk <key>= or re-enter in the picker. [[https://bbs.archlinux.org/viewtopic.php?id=306757][arch 306757]]
- Pure WPA3-SAE won't associate (no). "No PSK available for association" / "SME: Failed to set WPA key management" on a WPA3-only AP. The profile defaults to WPA-PSK key-mgmt with no PMF, which a pure-SAE AP rejects. Fix: =nmcli con modify <name> wifi-sec.key-mgmt sae 802-11-wireless-security.pmf 3=. [[https://bbs.archlinux.org/viewtopic.php?id=256573][arch 256573]]
- PMF mismatch on a WPA2/WPA3 transition AP (no). SAE assoc rejected on mixed-mode; connects to WPA2 but not the SAE path. Transition mode requires PMF-capable and rejects SAE when 802.11w isn't negotiated. Fix: match the AP's PMF — =nmcli con modify <name> 802-11-wireless-security.pmf 2=. [[https://hostap.shmoo.narkive.com/38Iowl2x/ieee-802-11w-support-in-wpa-supplicant-management-frame-protection-required-but-client-did-not][hostap 802.11w]]
- SAE H2E-only AP vs hunt-and-peck client (yes). WPA3 assoc fails "unspecified failure" on a Hash-to-Element-only AP. wpa_supplicant defaults to hunt-and-peck; the PWE method mismatches. Fix: =sae_pwe=2= in wpa_supplicant global config. [[https://wiki.archlinux.org/title/Wpa_supplicant][archwiki wpa_supplicant]]
- eduroam PEAP cert validation failed (no). "Certificate verification failed"; EAP drops. Missing/wrong CA cert, or NM ignoring system CA certs. Fix: set the correct CA cert / server-name in 802-1x (temporarily =system-ca-certs=false= to test). [[https://debianforum.de/forum/viewtopic.php?t=169560][debianforum 169560]]
- iwd eduroam bad_certificate (no). iwd refuses eduroam "bad_certificate" though it works elsewhere. iwd's EAP needs the server CA cert and a matching domain. Fix: add =EAP-PEAP-CACert=<ca.pem>= (and Domain/ServerDomainMask) to the iwd profile. [[https://bbs.archlinux.org/viewtopic.php?id=291921][arch 291921]]
- 802.1X won't save/verify the CA cert (no). Enterprise wifi only connects with "No CA certificate required" ticked. NM wants a PEM (not DER) bundle and mishandles the ca-cert setting. Fix: =nmcli con modify <name> 802-1x.ca-cert /etc/ssl/certs/ca-certificates.crt=. [[https://bugzilla.redhat.com/show_bug.cgi?id=1455833][redhat 1455833]]
- Wrong eduroam anonymous/outer identity (no). Auth rejected at the RADIUS server. The outer identity has the wrong realm, or the anonymous ID is reused as the inner identity. Fix: set =anonymous_identity="anonymous@realm"= and =identity="user@realm"= to the home realm. [[https://community.jisc.ac.uk/library/network-and-technology-service-docs/2021-04-advisory-android-11-configuration-issues][jisc eduroam]]
- Hidden SSID never connects (no). A saved non-broadcast SSID doesn't auto-connect; "No network with SSID found". NM won't send a directed probe unless the profile is flagged hidden. Fix: =nmcli con modify <name> wifi.hidden yes=. [[https://bbs.archlinux.org/viewtopic.php?id=39839][arch 39839]]
- Randomized MAC breaks captive portal / MAC allow-list (no; merges the NM-layer duplicate). Connects but the portal re-prompts every time, or a MAC-filtered router refuses the device. Per-connection random MAC changes each connect. Fix: =nmcli con modify <name> wifi.cloned-mac-address stable= (or =permanent=). [[https://fedoramagazine.org/randomize-mac-address-nm/][fedora NM MAC]]
- scan-rand-mac-address breaks scan/assoc on some drivers (yes). After an NM upgrade no networks appear, or assoc fails "Authentication timeout" (ath9k/ath9k_htc, some Realtek/Atheros). The driver can't handle the randomized scan MAC. Fix: =[device] wifi.scan-rand-mac-address=no= drop-in. [[https://github.com/qca/open-ath9k-htc-firmware/issues/132][qca ath9k-htc 132]]
- Wrong regulatory domain hides/blocks channels (yes). A 5GHz AP is invisible / "no suitable AP"; the card won't use the AP's channels. Regulatory domain unset or wrong, so the kernel forbids those frequencies. Fix: =iw reg set <CC>=, persist via =WIRELESS_REGDOM= (install wireless-regdb). [[https://bbs.archlinux.org/viewtopic.php?id=249979][arch 249979]]
- Won't roam, stuck on a weak AP (no). The client clings to a weak BSSID even with a stronger same-SSID AP in range. NM+wpa_supplicant roaming is conservative. Fix: bounce the connection, tune bgscan / lock a bssid, or try the iwd backend. [[https://bbs.archlinux.org/viewtopic.php?id=291466][arch 291466]]
- 4-way-handshake timeout / deauth loop, reason 15 (both). "4way_handshake_timeout" or repeated deauth (Reason 15) on iwlwifi/some drivers. An 802.11n handshake bug or AP port-security kicks the client mid-handshake. Fix: =options iwlwifi 11n_disable=1= (reboot), or try the other backend. [[https://bbs.archlinux.org/viewtopic.php?id=264378][arch 264378]]
- iwd associates but NM(wpa_supplicant) doesn't (yes; see also the NM backend entries). Standalone iwd connects but NM's wpa_supplicant path fails to associate on the same AP. Backend-specific supplicant behavior differs. Fix: =[device] wifi.backend=iwd= drop-in, disable standalone iwd.service, restart NM. [[https://bbs.archlinux.org/viewtopic.php?id=292603][arch 292603]]

** IP / DHCP / gateway / routing / VPN policy

- dhcpcd competing with NM's internal DHCP client (yes; merges the two DHCP-conflict duplicates). Interface never gets an IPv4 address; NM stuck "getting IP configuration". A standalone =dhcpcd.service= and NM's internal client fight over the interface. Fix: =systemctl disable --now dhcpcd= and let NM own DHCP. [[https://bbs.archlinux.org/viewtopic.php?id=165793][arch 165793]]
- dhcpcd 9 backend breaks NM IPv4 (yes). No IPv4 after a dhcpcd upgrade; IPv6 may still work. NM's dhcpcd backend was incompatible with dhcpcd 9's changed behavior. Fix: =dhcp=internal= in NetworkManager.conf (or NM ≥1.30.4-3), restart NM. [[https://bugs.archlinux.org/task/66231][arch fs66231]]
- APIPA / link-local only, no DHCP answer (no). The interface self-assigns 169.254.x.x; only local-link hosts reachable. No DHCP server answered in the timeout. Fix: re-trigger DHCP — =nmcli device reapply <dev>=; a recurring case is a server-side fault. [[https://oneuptime.com/blog/post/2026-03-20-fix-apipa-169-254-address/view][apipa 169.254]]
- Default route never installed by the connection (yes). Has an IP and pings the LAN, but no default route. The profile has =ipv4.never-default yes= ("use only for resources on its network"). Fix: =nmcli con modify <name> ipv4.never-default no=, up. [[https://bbs.archlinux.org/viewtopic.php?id=84453][arch 84453]]
- DHCP gateway in a different subnet than the lease (yes). IP assigned but no default route; "SIOCADDRT: No such process". The DHCP-offered gateway is off the assigned prefix, so the on-link route is refused. Fix: add the on-link route then default (=ip route add <gw> dev <iface>; ip route add default via <gw>=), or fix the DHCP scope. [[https://bbs.archlinux.org/viewtopic.php?id=72685][arch 72685]]
- Duplicate IPv4 on the LAN, address skipped by ACD (yes). Connection comes up but no usable address; journal logs the conflicting MAC. NM's RFC 5227 conflict detection found the IP already in use. Fix: change the offending host / DHCP reservation, or set a distinct static IP. [[https://bbs.archlinux.org/viewtopic.php?id=287424][arch 287424]]
- IPv6 RA not received, no SLAAC address or route (yes). No IPv6 address/route; interface hangs "configuring". =accept_ra=0=, forwarding enabled without =accept_ra=2=, or an upstream RA-guard drops ICMPv6 type 134. Fix: =sysctl net.ipv6.conf.<iface>.accept_ra=2= (or unblock RA at the router). [[https://oneuptime.com/blog/post/2026-03-20-ipv6-ra-not-received/view][ipv6 ra]]
- DHCPv6-only network, address but no route (yes). An IPv6 address via stateful DHCPv6, but no default route. Routing lives in the RA, not DHCPv6. Fix: ensure the router sends an RA with the M flag and let NM process both (=ipv6.method auto=). [[https://bbs.archlinux.org/viewtopic.php?id=273336][arch 273336]]
- Happy-eyeballs stall on broken IPv6 (no; the routing angle — see also the DNS AAAA and egress v6 entries). Pages load with a visible hang; IPv6 is present but black-holed. Dual-stack apps race IPv6 first and wait to fall back. Fix: =nmcli con modify <name> ipv6.method disabled= (or fix the upstream v6 path). [[https://oneuptime.com/blog/post/2026-03-20-ipv6-happy-eyeballs-issues/view][happy-eyeballs]]
- WireGuard AllowedIPs=0.0.0.0/0 strands the host when the tunnel drops (no). Everything offline after the VPN drops; ping and DNS fail. Full-tunnel installed a default route through wg0 with no live peer. Fix: bring the tunnel down (=wg-quick down <iface>= / =nmcli con down <vpn>=) to restore the physical route. [[https://discourse.coreelec.org/t/wireguard-client-not-connected-when-allowedips-0-0-0-0-0/18187][wg allowedips]]
- WireGuard split-tunnel misconfig captures the LAN (yes). VPN connects but LAN devices/printers become unreachable. =AllowedIPs=0.0.0.0/0= used where a split tunnel was intended. Fix: set AllowedIPs to only the intended subnets, re-up. [[https://oneuptime.com/blog/post/2026-03-20-wireguard-allowedips-ipv4-split-tunneling/view][wg split-tunnel]]
- OpenVPN redirect-gateway route left behind after an abnormal disconnect (yes). No internet/DNS after the tunnel dies; can't even reconnect. redirect-gateway rewrote the default route and a hard link-down never restored it. Fix: =ip route del default dev tun0; systemctl restart openvpn-client@<name>= (use =def1= going forward). [[https://forums.openvpn.net/viewtopic.php?t=22572][openvpn redirect-gw]]
- Tailscale exit node captures the default route (no). Internet dies after selecting an exit node; tailnet peers still reachable. The exit-node route conflicts with the working one, or policy lacks =autogroup:internet=. Fix: =tailscale set --exit-node== to drop back to the local default route. [[https://github.com/tailscale/tailscale/issues/2654][tailscale exitnode]]
- Docker bridge subnet collides with a real external subnet (yes). A specific external host (172.17.x.x) is unreachable while the rest of the internet works. docker0 claimed 172.17.0.0/16. Fix: set ="bip": "172.26.0.1/16"= in daemon.json, prune, restart docker. [[https://github.com/moby/moby/issues/36619][moby 36619]]
- libvirt virbr0 subnet collides with the real network (yes). Host/VMs can only reach the bridge/host, not the WAN. virbr0 came up on a range overlapping the LAN. Fix: re-address the virtual net via =virsh net-edit default=, destroy/start it. [[https://bugzilla.redhat.com/show_bug.cgi?id=811967][rhbz 811967]]
- Wifi + ethernet up with conflicting metrics, traffic exits the dead link (yes). Intermittent/no connectivity with two links up; egress uses the wrong interface. Both installed a default route and the lower metric wins even when it can't reach the internet. Fix: raise the bad link's metric — =nmcli con modify <name> ipv4.route-metric <higher>=. [[https://www.baeldung.com/linux/change-network-routing-metric][route-metric]]

** DNS / resolver / DoT / DNSSEC

- Dangling resolv.conf symlink after resolved is disabled/not started (yes). Can ping 1.1.1.1 but nothing resolves; =/etc/resolv.conf= symlinks to a stub file that doesn't exist. The stub only exists while systemd-resolved runs. Fix: =systemctl enable --now systemd-resolved= (or repoint the link at a real file). [[https://github.com/systemd/systemd/issues/5395][systemd 5395]]
- resolv.conf not pointing at the stub while resolved runs (yes). Names fail though resolved is up; resolv.conf is a stale static file. An installer/upgrade replaced it. Fix: =ln -sf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf=, verify with =resolvectl status=. [[https://wiki.archlinux.org/title/Systemd-resolved][archwiki resolved]]
- systemd-resolved stub 127.0.0.53 unreachable / port 53 conflict (yes). resolv.conf says 127.0.0.53 but every query is connection-refused. A second resolver (dnsmasq, bind) holds port 53, so the stub never binds. Fix: stop the conflicting resolver or set DNSStubListener, restart resolved. [[https://github.com/systemd/systemd/issues/10298][systemd 10298]]
- NetworkManager not integrated with resolved (yes). resolved is up but knows no upstream servers; NM writes its own resolv.conf. =dns=systemd-resolved= not set, so DHCP servers never reach resolved. Fix: add =dns=systemd-resolved= under [main] in NetworkManager.conf, restart NM. [[https://wiki.archlinux.org/title/Systemd-resolved][archwiki resolved]]
- DNSSEC=yes rejects a non-compliant venue resolver (yes). Pages won't load on hotel/ISP wifi though ping works; "DNSSEC validation failed". resolved rejects the venue resolver that mangles DNSSEC records. Fix: =DNSSEC=allow-downgrade= (or no) in resolved.conf, restart resolved. [[https://bbs.archlinux.org/viewtopic.php?id=240427][arch 240427]]
- DNSSEC "no-signature" verdict sticks after a network change (yes). Resolution dies sporadically after reconnecting; resolved reuses a cached bogus/downgrade verdict from the previous network. Fix: =resolvectl reset-server-features= (and flush), or DNSSEC=allow-downgrade. [[https://github.com/systemd/systemd/issues/12388][systemd 12388]]
- DoT strict mode with port 853 blocked (yes). Everything stalls; DNSOverTLS=yes forbids fallback and the network drops 853. Fix: =DNSOverTLS=opportunistic= (or no) in resolved.conf, restart resolved. [[https://wiki.archlinux.org/title/Systemd-resolved][archwiki resolved]]
- DoT strict to an unreachable / cert-mismatched server (yes). "Failed to invoke gnutls_handshake: Error in the certificate verification"; the pinned DoT server is down or MITM'd. Strict mode plus IP#hostname pinning rejects the cert and won't fall back. Fix: correct the server/#hostname, switch provider, or relax to opportunistic, restart resolved. [[https://github.com/systemd/systemd/issues/16531][systemd 16531]]
- DHCP handed a broken resolver (no). Nothing resolves on one network though egress works; the DHCP DNS server is dead/filtering. Fix: =nmcli con mod <con> ipv4.ignore-auto-dns yes ipv4.dns "1.1.1.1 9.9.9.9"=, up. [[http://adam.younglogic.com/2019/05/using-nmcli-to-set-nameservers/][nmcli dns]]
- Manually-pinned 8.8.8.8 blocked by the venue (no). A hard-set public DNS resolves nothing though 1.1.1.1 pings; the network blocks external port 53. Fix: drop the manual pin and use DHCP DNS (=ipv4.ignore-auto-dns no=, clear =ipv4.dns=), reconnect. [[https://forum.netgate.com/topic/187060/port-53-dns][netgate port 53]]
- Stale poisoned cache after captive-portal login (yes). First lookups after the portal keep returning the portal/blocked address. Pre-login hijacked answers were cached. Fix: =resolvectl flush-caches=. [[https://oneuptime.com/blog/post/2026-03-20-flush-dns-cache-linux-macos-windows/view][flush-caches]]
- VPN split-DNS not applied / leaks to the ISP resolver (no). Internal/corp names fail (or a censored ISP resolver still answers) after connecting the VPN. NM/resolved didn't install the VPN link's domain as a routing domain. Fix: =resolvectl domain <vpn-link> '~corp.example'= and =resolvectl default-route <vpn-link> false=. [[https://blogs.gnome.org/mcatanzaro/2020/12/17/understanding-systemd-resolved-split-dns-and-vpn-configuration/][catanzaro split-dns]]
- IPv6 AAAA lookups stall resolution (yes; the DNS angle of the broken-v6 family). Every name takes ~5s then works; A and AAAA go in parallel and AAAA is never answered. Broken/half-configured IPv6 swallows the AAAA query. Fix: fix or disable IPv6 on the link, or =options single-request timeout:1=. [[https://bbs.archlinux.org/viewtopic.php?id=262926][arch 262926]]
- Another daemon overwrites resolv.conf (yes). DNS works then breaks (or breaks after VPN up/down) as dhcpcd/openvpn/openresolv rewrites resolv.conf. Multiple tools claim it with no coordination. Fix: pick one manager (openresolv =resolvconf=NO=, dhcpcd =nohook resolv.conf=), point resolv.conf at the stub, restart resolved. [[https://github.com/adrienverge/openfortivpn/issues/674][openfortivpn 674]]
- nsswitch.conf hosts line broken (yes). All resolution fails, or LAN/mDNS names never resolve; the hosts line lacks =resolve=/=dns= in the right order or references an uninstalled nss module. Fix: set =hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns=. [[https://man.archlinux.org/man/nss-resolve.8.en][nss-resolve]]
- Avahi/.local mDNS not resolving (yes). *.local names don't resolve though unicast DNS works. nss-mdns not wired in, or resolved's built-in mDNS collides with avahi. Fix: install nss-mdns, add =mdns_minimal [NOTFOUND=return]= before =resolve=, enable avahi-daemon, disable resolved MulticastDNS if both run. [[https://wiki.archlinux.org/title/Avahi][archwiki avahi]]

** Egress / captive portal / MTU / proxy / clock / upstream

- Captive portal held state, no auto-popup (no). Wifi associates and gets a lease but every site fails; no login window appears. Without a DE NetworkManager integration or a dispatcher script, NM detects the PORTAL state but nothing opens the login page. Fix: open a plain-HTTP probe (=xdg-open http://neverssl.com=) or the URL NM reports; add an nm-dispatcher script to auto-launch. [[https://wiki.archlinux.org/title/NetworkManager#Captive_portals][archwiki captive portals]]
- Connectivity check over HTTPS never triggers the portal redirect (no). Behind a portal the login popup never fires. NM's connectivity URI was probed over HTTPS, which the portal can't transparently redirect. Fix: point NM's check at an HTTP URI (=20-connectivity.conf= =uri=http://…=) and open a plain-HTTP page. [[https://bugzilla.redhat.com/show_bug.cgi?id=1252839][redhat 1252839]]
- Custom DNS / DoT / DNSSEC hides the captive portal (yes). No portal page ever resolves and the machine stays cut off. resolved pinned to 1.1.1.1 with DoT/DNSSEC bypasses the portal's DNS hijack, so lookups just fail. Fix: drop DoT/DNSSEC for the captive network (=resolvectl dnsovertls <iface> no; resolvectl dnssec <iface> no=), log in, restore. [[https://github.com/systemd/systemd/issues/27485][systemd 27485]]
- HSTS blocks the portal redirect in the browser (no). The login page won't load; the browser shows a cert/HSTS error instead of the form. The first site was HSTS-pinned, so the browser refuses the portal's HTTP redirect. Fix: browse to a non-HSTS plain-HTTP address (http://neverssl.com, http://captive.apple.com). [[https://community.ui.com/questions/Solution-for-HSTS-issues-with-captive-portal/17b033e7-3dfe-4830-af8f-bf6ead23d8b0][ui hsts portal]]
- PMTUD blackhole from dropped ICMP (no; merges the IP-layer duplicate). Small requests and DNS work, pages start then stall, large downloads/SSH hang. A middlebox drops ICMP "fragmentation needed", so PMTUD never learns the real MTU and oversized packets vanish. Fix: lower the interface MTU (=nmcli con modify <con> 802-11-wireless.mtu 1400=), or MSS-clamp. [[https://ipfyi.com/scenario/path-mtu-blackhole/][pmtud blackhole]]
- PPPoE / VPN link with a lower MTU not clamped (no). Browsing works but big transfers / some HTTPS hang. A PPPoE (1492) or VPN path has a smaller MTU and the too-large segments get dropped. Fix: set the tunnel/link MTU down (=.mtu 1420= for VPN, 1492 for PPPoE) or MSS-clamp on the gateway. [[https://thelineman.ca/articles/article-8-mtu-vpn-mss][vpn mtu/mss]]
- Stale http_proxy env var points at a dead proxy (no). Every curl/wget/pacman fails though the network is fine; browsers may work. A leftover =http_proxy= points at an offline/off-network proxy. Fix: unset the vars, remove the export from =~/.profile= / =/etc/environment=. [[https://everything.curl.dev/usingcurl/proxies/env.html][curl proxy env]]
- Unreachable PAC file off the corporate network hangs everything (no). Away from the office the browser stalls with no error. A system proxy set to "automatic" with a PAC URL that only resolves on the corporate LAN blocks waiting instead of falling back to DIRECT. Fix: switch system proxy to None (=gsettings … org.gnome.system.proxy mode 'none'=) or clear the PAC URL. [[https://bugzilla.mozilla.org/show_bug.cgi?id=1121800][ff pac hang]]
- Clock skew breaks every TLS handshake (yes). "Your connection is not private" on every HTTPS site though ping/DNS work; the clock is hours/years off. A dual-boot Windows RTC-localtime, unsynced NTP, or a dead CMOS battery leaves the clock wrong. Fix: =timedatectl set-ntp true= (=set-local-rtc 0= on dual-boot), replace the CMOS battery if it recurs. [[https://wiki.archlinux.org/title/System_time][archwiki system time]]
- Firewall default-deny drops all egress (yes). No traffic leaves right after enabling a firewall, or after both ufw and firewalld are on; even DNS fails. A default outgoing-deny policy, or two firewalls fighting over nftables. Fix: allow egress (=ufw default allow outgoing=) and run only one firewall. [[https://wiki.archlinux.org/title/Uncomplicated_Firewall][archwiki ufw]]
- VPN kill-switch / leftover iptables rule strangles egress after VPN drops (yes; distinct from the route-capture case). Internet dies the moment the VPN disconnects and never returns until reboot. A kill-switch rule pinned traffic to tun0 and the leftover rule keeps dropping everything on the real interface. Fix: flush the stale rules (=iptables -F; iptables -P OUTPUT ACCEPT=, or restart the firewall), reconnect. [[https://bbs.archlinux.org/viewtopic.php?id=300104][arch ufw killswitch]]
- IPv6 egress broken while IPv4 works (no; the egress angle of the broken-v6 family). Pages load slowly/intermittently; IPv4-only hosts are fine. The network advertises IPv6 with no working route and Happy Eyeballs keeps trying the dead AAAA path. Fix: =nmcli con modify <con> ipv6.method disabled= until the network's IPv6 is fixed. [[https://help.ubuntu.com/community/WebBrowsingSlowIPv6IPv4][ubuntu slow ipv6]]
- False "limited connectivity" from a local DNS/VPN service (no; merges the NM-layer connectivity-check duplicate). The applet shows "limited/no internet" and apps that gate on NM refuse to work, yet browsing functions. NM's check to its connectivity URI fails — a local Pi-hole/VPN blocks the probe host, a false negative. Fix: point =20-connectivity.conf= at a reachable 204 endpoint, or =[connectivity] enabled=false=, reload NM. [[https://bbs.archlinux.org/viewtopic.php?id=272292][arch nm limited]]
- ISP outage or modem stuck in a bad state — not locally fixable (physical). Everything downstream is "connected, no internet"; the router's WAN IP is 0.0.0.0. The upstream link is down or the modem latched into a bad state. The doctor must recognize this and STOP. Fix: power-cycle modem then router; check ISP status / contact the provider. [[https://whizz-tech.com/support/wifi-router-fixes/wifi-stops-working-after-power-outage/][modem bad state]]
- Specific outbound port blocked while web works (no). Browsing is fine but email won't send or a service times out. The network/ISP blocks that port (SMTP 25, some VPN ports). A partial block, not a full outage. Fix: use an allowed alternate (submission 587, VPN over 443/TCP), or switch networks — the policy isn't host-fixable. [[https://help.dreamhost.com/hc/en-us/articles/217071167-Port-25-Blocking][port 25 blocking]]

** NetworkManager control plane / backends / config

- NetworkManager service masked or failed to start (yes). No networking at all; "Unit NetworkManager.service is masked" or the unit dies immediately. The unit was masked, or an invalid unit file / malformed NetworkManager.conf blocks startup. Fix: =systemctl unmask NetworkManager && systemctl start NetworkManager=; reinstall if the unit is corrupt, validate the conf. [[https://bbs.archlinux.org/viewtopic.php?id=193036][arch 193036]]
- NetworkManager segfaults and restart-loops (yes). Connectivity drops intermittently; journal "Failed with result 'core-dump'" and repeated respawns. A bug in the running NM build crashes the daemon. Fix: =coredumpctl info NetworkManager=, then update/downgrade the package, restart NM. [[https://bbs.archlinux.org/viewtopic.php?id=236562][arch 236562]]
- iwd and wpa_supplicant both active, backends fight (both). Wifi scans but never associates, or associates then drops; both daemons drive one radio. Fix: pick one backend, =systemctl disable --now= the other, set =[device] wifi.backend==, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=292603][arch 292603]]
- wifi.backend=iwd configured but iwd not installed/running (both). No wifi device appears at all; NM acts as if there's no radio. NM is told to use iwd but the package isn't installed or its service can't start. Fix: =pacman -S iwd= (or remove the drop-in to fall back), reboot. [[https://bbs.archlinux.org/viewtopic.php?id=305442][arch 305442]]
- systemd-networkd and NetworkManager both managing the link (both). The interface gets an IP then loses it, or flaps; two managers own one NIC. Fix: =systemctl disable --now systemd-networkd systemd-networkd.socket= (mask if dbus-activated), reboot. [[https://bbs.archlinux.org/viewtopic.php?id=184164][arch 184164]]
- Keyfile permissions void a saved connection (yes). A saved network shows in nmcli but never activates; journal marks it insecure and skips it. The =.nmconnection= isn't 600 root-owned. Fix: =chmod 600= and =chown root:root= the file in system-connections, =nmcli connection reload=. [[https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html/configuring_and_managing_networking/assembly_networkmanager-connection-profiles-in-keyfile-format_configuring-and-managing-networking][rhel keyfile]]
- Autoconnect disabled on the profile (no). The network works when activated by hand but never comes up on boot/resume. =connection.autoconnect=no=. Fix: =nmcli connection modify <name> connection.autoconnect yes= (user-scope). [[https://bbs.archlinux.org/viewtopic.php?id=281611][arch 281611]]
- Duplicate/conflicting profiles for one SSID (no). Two entries for the same network; the wrong one activates. Leftover =.nmconnection= files created a second profile with conflicting settings. Fix: =nmcli connection delete <uuid>= the stale one, or raise the good one's =autoconnect-priority=. [[https://bbs.archlinux.org/viewtopic.php?id=274552][arch 274552]]
- A dispatcher script errors and blocks connectivity (yes). Network events don't complete, or a connectivity hook silently doesn't run. A script in dispatcher.d fails on a permission/ownership problem or loops. Fix: make it root-owned and non-group-writable or remove it; debug via =journalctl -u NetworkManager-dispatcher=. [[https://man.archlinux.org/man/NetworkManager-dispatcher.8.en][arch dispatcher]]
- Polkit won't authorize a non-root user to control networking (no). =nmcli= up/modify fails "Not authorized to control networking". No polkit agent, or the login has no active seat session. Fix: start a polkit agent and ensure a proper loginctl session (relogin via the display manager), or add a polkit rule. [[https://bbs.archlinux.org/viewtopic.php?id=141465][arch 141465]]
- No reconnect after suspend/resume (yes). After waking, wifi/wired stays down until the service is kicked. On resume NM doesn't re-establish the link. Fix: =systemctl restart NetworkManager= (the doctor's nm-restart); durable fix is a system-sleep hook. [[https://bbs.archlinux.org/viewtopic.php?id=234725][arch 234725]]
- NetworkManager-wait-online hangs boot (both). Boot stalls ~90s on NetworkManager-wait-online; the desktop is late. The service waits for connectivity that never arrives (unplugged NIC, non-autoconnect port). Fix: =systemctl disable NetworkManager-wait-online.service= (or drop the unused profile); effective next boot. [[https://bbs.archlinux.org/viewtopic.php?id=298817][arch 298817]]

* Bluetooth failure modes

Five layers, mirroring the bt doctor's chain (adapter present → rfkill → bluetooth.service → adapter powered → per-device → audio profile). ~70 raw entries from the sweep; hardware-block duplicates (a Bluetooth hard-block appears in every one of the first three layers) and the pairing/connection overlaps are merged inline, leaving ~55 distinct root causes.

** Adapter / hardware / driver / firmware

- btusb module not auto-loaded (yes). lsusb shows the adapter but no hci0, =/sys/class/bluetooth= empty, "No default controller available". btusb didn't load at boot (missing modules-load entry or a blacklist). Fix: =modprobe btusb=, persist via =/etc/modules-load.d/bluetooth.conf=. [[https://bbs.archlinux.org/viewtopic.php?id=267428][arch 267428]]
- Intel ibt-*.sfi firmware missing/mismatched (both). No controller; dmesg "Direct firmware load for intel/ibt-NN-N.sfi failed with error -2". linux-firmware lacks the exact .sfi/.ddc the controller requests. Fix: update linux-firmware (or symlink the requested name), reboot. [[https://bbs.archlinux.org/viewtopic.php?id=302314][arch 302314]]
- Intel "Failed to send firmware data" during load (both). Adapter present then dies; "hci0: Failed to send firmware data (-38)/(-110)". Firmware transfer aborts (USB/init timing, often kernel-specific). Fix: =options btusb reset=1= and reload, or downgrade the kernel, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=248784][arch 248784]]
- Intel AX200/AX210 controller lost after a kernel update (both). WiFi fine, BT gone, "No default controller available" right after an upgrade. A kernel/firmware regression stops the BT half enumerating. Fix: boot linux-lts or downgrade until fixed, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=282611][arch 282611]]
- Intel broken-initial-NCMD init hang (both). "hci0: command tx timeout" during setup; the controller never comes up. Some Intel controllers need the BTUSB_INTEL_BROKEN_INITIAL_NCMD quirk absent on older kernels. Fix: run a kernel new enough to carry the quirk, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=226312][arch 226312]]
- MediaTek MT7921/MT7961 firmware filename mismatch (both). No adapter; "Direct firmware load for mediatek/BT_RAM_CODE_MT7961_1a_2_hdr.bin failed with error -2". linux-firmware ships the blob compressed or under a different name. Fix: decompress/rename to the requested file, reload btusb, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=296026][arch 296026]]
- MediaTek MT7922 btmtk regression after a kernel bump (both). BT stopped initializing after a specific kernel; WiFi unaffected. A regression in the mt7921e/btmtk path. Fix: downgrade to the last working kernel (or linux-lts), reboot. [[https://bbs.archlinux.org/viewtopic.php?id=313561][arch 313561]]
- MediaTek MT7922 stuck in a residual power state (physical). "No Bluetooth adapters found" persists across warm reboots; only a full power-off clears it. The controller latched in a bad state a soft reboot doesn't reset. Fix: shut down, pull power ~10s, cold boot. [[https://bbs.archlinux.org/viewtopic.php?id=308169][arch 308169]]
- MediaTek MT7920/MT7922 bogus firmware in linux-firmware (both). WiFi works, BT half fails "Failed to set up firmware" after a linux-firmware update. A shipped BT blob is broken in the current package. Fix: downgrade linux-firmware-mediatek to the prior version, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=311544][arch 311544]]
- MediaTek MT7925 killed by aggressive USB autosuspend (both). BT flaky/absent on a recent kernel; "Opcode 0x0c03 failed: -16". Kernel power-saving suspends the controller. Fix: =usbcore.autosuspend=-1 btusb.enable_autosuspend=n= on the kernel cmdline, reboot. [[https://bbs.archlinux.org/viewtopic.php?id=306366][arch 306366]]
- Realtek RTL8761B(U) firmware name mismatch (yes). USB dongle dead; driver requests rtl_bt/rtl8761bu_fw.bin but firmware ships rtl8761b_fw.bin. Fix: symlink to the bu names in /lib/firmware/rtl_bt (or update linux-firmware), replug — no reboot. [[https://bbs.archlinux.org/viewtopic.php?id=309671][arch 309671]]
- Realtek RTL8852BU/newer dongle needs an out-of-tree driver (both). A recent combo dongle isn't recognized at all; no in-kernel support. Fix: build the vendor DKMS driver (lwfinger/rtl8852bu), reboot. [[https://github.com/lwfinger/rtl8852bu][rtl8852bu]]
- Fake/clone CSR dongle resets and times out (yes). A cheap 0a12:0001 "CSR" dongle works briefly then "command tx timeout"; "Unbranded CSR clone detected". A counterfeit controller mishandles CSR reset. Fix: rely on the kernel clone quirks, or =options btusb reset=1 enable_autosuspend=0=, reload btusb. [[https://bbs.archlinux.org/viewtopic.php?id=272230][arch 272230]]
- Qualcomm WCN6855/QCA6390 version read fails (both). No BT; "Reading QCA version information failed (-110)" via ath11k. Missing/mismatched QCA firmware or a btqca init-timing bug. Fix: update linux-firmware and run a newer kernel (or reload ath11k_pci/btusb), reboot. [[https://bbs.archlinux.org/viewtopic.php?id=284506][arch 284506]]
- Broadcom BCM .hcd patch file missing (both). Adapter enumerates then stalls; "hci0: BCM: Patch brcm/BCMxxxxx-….hcd not found". The .hcd firmware isn't in linux-firmware. Fix: install broadcom-bt-firmware (AUR) or drop the correct .hcd into /lib/firmware/brcm, reboot. [[https://github.com/winterheart/broadcom-bt-firmware/issues/30][broadcom-bt-fw 30]]
- USB autosuspend powers the adapter off after suspend/idle (both; the hardware angle — see also the resume entry in the rfkill layer). BT works at boot, then hci0 vanishes after a suspend/resume or idle; only a full shutdown restores it. btusb autosuspend cuts power and the controller doesn't recover. Fix: =btusb.enable_autosuspend=0= on the kernel cmdline (or exclude the device in TLP), reboot. [[https://forum.manjaro.org/t/bluetooth-adapter-disappears-after-suspend-only-shutdown-can-fix/157919][manjaro 157919]]
- Bluetooth hard-blocked by a BIOS/hardware switch (physical; the canonical hard-block — appears identically across the rfkill layer). No adapter and =rfkill list= shows Bluetooth "Hard blocked: yes" (or hci0 absent) after a wireless switch/Fn toggle or a BIOS setting. Fix: flip the physical switch / Fn key, or enable Bluetooth in BIOS/UEFI — no software can clear a hard block. [[https://github.com/systemd/systemd/issues/4117][systemd 4117]]

** rfkill / power / service

- Soft-blocked adapter needs manual unblock (no). =rfkill list= shows Bluetooth "Soft blocked: yes"; bluetoothctl "Failed to set power on: org.bluez.Error.Failed". A prior software toggle left the soft-block set and bluetoothd won't power a blocked adapter. Fix: =rfkill unblock bluetooth= (then =bluetoothctl power on=). [[https://bbs.archlinux.org/viewtopic.php?id=169530][arch 169530]]
- AutoEnable off leaves BT powered down every boot (yes). Adapter present and service running, but "Powered: no" at every login. bluez main.conf has AutoEnable=false (also the static default when main.conf is absent), so bluetoothd never powers the controller. Fix: =AutoEnable=true= under [Policy] in main.conf, restart bluetooth. [[https://github.com/bluez/bluez/issues/886][bluez 886]]
- bluetooth.service masked (yes). =systemctl start bluetooth= returns "Unit bluetooth.service is masked". The unit was masked by an earlier disable or a tuning guide. Fix: =systemctl unmask bluetooth.service && systemctl enable --now bluetooth=. [[https://bbs.archlinux.org/viewtopic.php?id=220081][arch 220081]]
- bluetooth.service not enabled at boot (yes). BT works after a manual start but is "inactive (dead)" on every fresh boot. On Arch the service ships disabled, so nothing starts bluetoothd at boot. Fix: =systemctl enable --now bluetooth.service=. [[https://bbs.archlinux.org/viewtopic.php?id=287428][arch 287428]]
- D-Bus policy blocks bluetoothd from owning org.bluez (yes). "D-Bus setup failed: Connection is not allowed to own the service 'org.bluez'"; bluetoothctl can't reach bluez. A missing/broken =/usr/share/dbus-1/system.d/bluetooth.conf= policy (partial install/upgrade). Fix: reinstall bluez to restore the policy, restart dbus and bluetooth. [[https://bbs.archlinux.org/viewtopic.php?id=283337][arch 283337]]
- bluez upgrade leaves a bad unit-file setting (yes). After a bluez update "Unit bluetooth.service has a bad unit file setting". A changed ExecStart path or a removed option in the shipped unit breaks parsing until daemon-reload. Fix: reconcile the .pacnew, correct ExecStart to =/usr/lib/bluetooth/bluetoothd=, =daemon-reload && restart bluetooth=. [[https://github.com/bluez/bluez/issues/736][bluez 736]]
- Airplane mode / physical switch hard-blocks BT (physical; the rfkill-layer view of the shared hard-block). =rfkill list= "Hard blocked: yes"; software toggles and unblock do nothing. A physical/firmware kill switch, Fn key, or BIOS airplane state holds the block. Fix: turn airplane mode off / flip the switch, or enable BT in BIOS. [[https://bugzilla.redhat.com/show_bug.cgi?id=713006][rh 713006]]
- WiFi rfkill toggle also kills BT on a combo chip (no). Turning WiFi off drops Bluetooth too, and both come up soft-blocked at boot. A shared WiFi/BT combo exposes a coupled rfkill so the wlan block cascades. Fix: =rfkill unblock bluetooth= after the toggle; unblock all at boot. [[https://forum.artixlinux.org/index.php/topic,5062.0.html][artix 5062]]
- TLP disables Bluetooth on startup (yes). BT is soft-blocked at every boot on a TLP laptop though the service is fine. TLP's =DEVICES_TO_DISABLE_ON_STARTUP= includes bluetooth (or RESTORE_DEVICE_STATE restores off). Fix: remove bluetooth from that list in =/etc/tlp.conf=; =rfkill unblock bluetooth= now. [[https://dev.to/sharafat/disable-bluetooth-at-startup-in-tlp-2k8d][tlp startup]]
- systemd-rfkill restores a stale soft-block at boot (yes). BT was on before shutdown but boots soft-blocked, or airplane-off never sticks. systemd-rfkill saved a blocked state to =/var/lib/systemd/rfkill= and reapplies it (a hotplug race can overwrite the good state). Fix: =rfkill unblock bluetooth=; clear the saved state (or mask systemd-rfkill if TLP owns radio state). [[https://github.com/systemd/systemd/issues/42148][systemd 42148]]
- rfkill block puts bluetoothd into a 100% CPU loop (yes). After =rfkill block bluetooth= (an airplane toggle) bluetoothd spins at 100% CPU and the adapter is unresponsive even after unblock. A bluez rfkill-handling regression busy-loops. Fix: =systemctl restart bluetooth= after unblocking; upgrade/downgrade bluez past the affected version. [[https://github.com/bluez/bluez/issues/785][bluez 785]]
- Adapter powers back off after a desktop-driven power-off (no). =bluetoothctl power on= fails specifically after BT was switched off in GNOME/desktop settings; only the desktop toggle restores it. The desktop's saved off-state re-blocks the adapter under the CLI. Fix: re-enable from the desktop toggle, or =rfkill unblock bluetooth= and power on. [[https://discourse.gnome.org/t/cannot-power-on-bluetooth-from-bluetoothctl-if-it-was-powered-off-from-the-gnome-settings/24782][gnome 24782]]
- BT soft-blocked/unresponsive on resume, needs a module reload (yes; distinct from the hardware-autosuspend case — here power state is stuck, not cut). After suspend/resume the adapter is lost or soft-blocked; toggling "shows" enabled but does nothing and restarting the service doesn't help. btusb fails to re-init on resume, leaving a stuck rfkill/power state. Fix: =rmmod btusb && modprobe btusb= (then restart bluetooth); automate via a post-resume sleep hook. [[https://forums.opensuse.org/t/btusb-broken-after-resuming-from-sleep/133499][opensuse 133499]]
- Wrong/missing default controller with multiple adapters (no; see also the multi-controller pairing case). "No default controller available" or commands hit the wrong hciN when a dongle and an onboard radio are both present. bluez picked a different default than the user wants. Fix: =bluetoothctl select <MAC>= then power on; pin it if needed. [[https://bbs.archlinux.org/viewtopic.php?id=286766][arch 286766]]

** Pairing / bonding

- Generic AuthenticationFailed on pair (no). "Failed to pair: org.bluez.Error.AuthenticationFailed" on an audio device. A half-written or contested bond from a prior attempt makes the device reject the new authentication. Fix: bluetoothctl disconnect, untrust, remove <mac>, restart bluetooth, pair from a clean scan; factory-reset the device if it persists. [[https://bbs.archlinux.org/viewtopic.php?id=267381][arch 267381]]
- Paired but not trusted, no auto-reconnect (no). Device pairs but never reconnects on its own after a reboot/power cycle; =info= shows "Trusted: no". bluez won't auto-accept a connection from an untrusted bond. Fix: =bluetoothctl trust <mac>=. [[https://techwiser.com/fix-bluetooth-device-doesnt-auto-connect-in-linux/][techwiser autoconnect]]
- Stale link key after a dual-boot re-pair (yes). A device paired in Windows no longer connects in Linux with AuthenticationFailed. A device stores one link key per host; re-pairing under the other OS overwrote it. Fix: =bluetoothctl remove <mac>= and pair again, or sync the keys between OSes (bt-dualboot / edit the LinkKey under /var/lib/bluetooth). [[https://armujahid.me/blog/dual-boot-bluetooth-pairing/][armujahid dualboot]]
- No default pairing agent registered (no). Pairing a PIN/keyboard device silently fails or the passkey prompt never appears (esp. headless). bluetoothctl's built-in agent is unregistered once it exits, so nothing answers the request. Fix: =agent on= then =default-agent= (or a persistent bt-agent / NoInputNoOutput agent for unattended Just Works). [[https://technotes.kynetics.com/2018/pairing-agents-bluez/][kynetics agents]]
- BLE device never appears in scan (no). A BLE peripheral shows in other OSes but never in =bluetoothctl scan=, while BR/EDR devices scan fine. The scan defaults to BR/EDR-only or LE isn't enabled. Fix: =menu scan / transport le= (or =btmgmt le on=); last resort =ControllerMode = le= in main.conf. [[https://bbs.archlinux.org/viewtopic.php?id=281064][arch 281064]]
- Corrupt device cache survives remove (yes). Repeated pairing failures for one device; =remove= reports success but the cache stays and the bad state returns. bluez doesn't fully purge =/var/lib/bluetooth/<adapter>/<mac>=. Fix: stop bluetooth, =rm -rf= the stale device dir, start bluetooth, pair fresh. [[https://github.com/bluez/bluez/issues/191][bluez 191]]
- ConnectionAttemptFailed / br-connection-page-timeout (yes). Pairing or first connect fails "Page Timeout" / "br-connection-page-timeout", often after a bluez upgrade. The daemon's baseband page times out; a version regression triggered it. Fix: =systemctl restart bluetooth= and retry; downgrade bluez if it recurs after an update. [[https://github.com/bluez/bluez/issues/230][bluez 230]]
- Re-pair loop: pairs then instantly disconnects (yes). Device pairs, drops within seconds, and re-pairing only works until the next attempt. A corrupt in-memory bond/device DB wedges the daemon. Fix: =rm -rf /var/lib/bluetooth/*= (or the device dir) and =systemctl restart bluetooth=, then pair once cleanly. [[https://bbs.archlinux.org/viewtopic.php?id=267233][arch 267233]]
- Headset un-pairs itself on disconnect (yes). A headset loses its bond every time it disconnects. The device sends an HID virtual_cable_unplug on disconnect and bluez treats it as an un-pair. Fix: pair again; no clean user setting — avoid fully powering the device off; restart bluetooth if the bond is gone. [[https://github.com/bluez/bluez/issues/2048][bluez 2048]]
- BLE address rotates every session (physical). A BLE device pairs once but can't reconnect; its address differs each power cycle. It uses a random/resolvable-private address, so a bond keyed to the old address won't match unless IRK resolution works. Fix: pair so the IRK is exchanged (bond, not just connect), or disable address privacy on the device; re-pair to the current identity. [[https://github.com/hbldh/bleak/issues/363][bleak 363]]
- Legacy keyboard needs the PIN typed on the device (physical). A legacy BT keyboard fails with an authentication timeout during pairing. It uses legacy PIN/passkey-entry: bluez shows a passkey that must be typed on the keyboard itself. Fix: register a KeyboardDisplay agent, type the displayed passkey on the keyboard, press Enter within the timeout. [[https://bbs.archlinux.org/viewtopic.php?id=174239][arch 174239]]
- Too many bonded devices, keys lost (yes). With many devices paired, after a reboot or dongle re-insert none connect. Past ~14 bonds bluez fails to restore the LTKs. Fix: =bluetoothctl remove= enough devices to drop below the limit, restart bluetooth. [[https://github.com/bluez/bluez/issues/201][bluez 201]]
- Dual-mode device pairs on the wrong transport (yes). A dual-mode device (AirPods) refuses to pair/connect because bluez tries BR/EDR when the device needs LE, with no per-device override. Fix: =ControllerMode = bredr= (or le) in main.conf [General], restart, pair, then restore =dual=. [[https://github.com/bluez/bluez/issues/514][bluez 514]]
- Adapter Pairable/Discoverable off (no). Scan finds nothing or the controller rejects pairing. The adapter has =Pairable: no= / =Discoverable: no=. Fix: =power on=, =pairable on=, =scan on= (or set the main.conf defaults). [[https://wiki.archlinux.org/title/Bluetooth][archwiki bt]]
- Target device not in pairing mode (physical). A peripheral never appears in scan though the adapter works. The device is powered but not advertising. Fix: hold the pairing button until the LED signals, re-run =scan on=. [[https://bbs.archlinux.org/viewtopic.php?id=261540][arch 261540]]
- Paired without a bond via blueman (no). A gamepad/mouse paired through blueman connects but is unusable, while bluetoothctl works. blueman completed pairing without establishing bonding, so no usable link key was stored. Fix: remove the device and =bluetoothctl pair <mac>= (which bonds), then trust and connect. [[https://github.com/blueman-project/blueman/issues/2219][blueman 2219]]

** Connection stability

- Xbox/PS controller drops seconds after connecting unless ERTM is off (both). A controller pairs and connects, then disconnects within seconds, repeatedly. bluez's Enhanced Retransmission Mode is incompatible with these controllers' L2CAP handling. Fix: =echo 1 > /sys/module/bluetooth/parameters/disable_ertm=, persist =options bluetooth disable_ertm=1= in modprobe.d, reboot. [[https://github.com/atar-axis/xpadneo/issues/295][xpadneo 295]]
- Paired+trusted device never reconnects on boot/resume (no). A trusted HID/audio device stays disconnected after boot or resume and needs a manual connect each time. AutoEnable only powers the adapter; it doesn't initiate outbound connections to peripherals that don't self-reconnect. Fix: install and enable bluetooth-autoconnect (a systemd service that connects trusted devices when the adapter powers on, including post-resume). [[https://github.com/jrouleau/bluetooth-autoconnect][bt-autoconnect]]
- ReconnectIntervals/AutoEnable policy leaves the link dead after a drop (yes). After a device drops out of range and returns, bluetoothd doesn't re-establish the link. The [Policy] AutoEnable and [GATT] ReconnectIntervals settings are unset or too sparse. Fix: set =AutoEnable=true= and =ReconnectIntervals=1,2,4,8,16,32,64= in main.conf, restart bluetooth. [[https://wiki.archlinux.org/title/Bluetooth][archwiki bt]]
- USB 3.0 port radio noise degrades BT on the same side of the chassis (physical). A BT mouse/headset stutters or drops, worst under USB load or with an external SSD in an adjacent USB3 port; SuperSpeed signaling adds ~20 dB of broadband noise across 2.4-2.5 GHz. Fix: move the dongle/device off the USB3 port (USB2 port or an extension cable to distance the receiver). [[https://www.usb.org/sites/default/files/327216.pdf][usb-if 327216]]
- WiFi/BT coexistence on a 2.4GHz combo chip causes stutter and drops (yes). On an AX200 (and similar combos) BT audio/HID stutters and 2.4GHz WiFi collapses when both radios are active, sharing one antenna path. Fix: move WiFi to 5GHz, or tune coexistence via =/etc/modprobe.d/iwlwifi.conf=, reload iwlwifi. [[https://community.intel.com/t5/Wireless/Wi-Fi-6-AX200-Bluetooth-causing-WiFi-to-disconnect-randomly/td-p/1437797][intel ax200]]
- btusb USB autosuspend causes input lag/dropout after idle (both; the connection-health view of the adapter-layer autosuspend cause). A BT mouse/keyboard lags or briefly disconnects after no input, then wakes sluggishly; the kernel autosuspends the btusb controller. Fix: =btusb.enable_autosuspend=0= on the kernel cmdline (or a udev =power/control=on= rule), reboot. [[https://community.frame.work/t/solved-bluetooth-mouse-lag-linux-autosuspend/26763][framework autosuspend]]
- Adapter dead / devices won't reconnect after suspend-resume (yes; the same resume-init failure the rfkill layer's module-reload entry names, from the device-connection side). After resume the adapter is gone or devices refuse to reconnect (dmesg shows btusb resume errors). The controller doesn't survive suspend/resume cleanly on some kernels. Fix: a systemd sleep hook that runs =rmmod btusb; modprobe btusb= (or restarts bluetooth) post-resume. [[https://bugzilla.redhat.com/show_bug.cgi?id=2100761][rh 2100761]]
- BLE device disconnects with reason 0x08 from a too-aggressive supervision timeout (yes). A BLE peripheral connects then drops after a few seconds with reason 0x08 (Timeout); the negotiated supervision timeout is too short for the interval and latency. Fix: raise it via =/sys/kernel/debug/bluetooth/hci0/supervision_timeout=, persist with a startup service (debugfs resets on reboot). [[https://bbs.archlinux.org/viewtopic.php?id=279872][arch 279872]]
- Realtek RTL8761B wrong-firmware reconnect-loop (yes; same root cause as the adapter-layer name-mismatch entry, manifesting as a fast reconnect loop). An RTL8761B/BU dongle disconnects and reconnects several times a second; autodetect requests the wrong firmware name (or a bad blob). Fix: symlink the correct blob in /lib/firmware/rtl_bt, reload btusb. [[https://bbs.archlinux.org/viewtopic.php?id=309671][arch 309671]]
- Disconnected/loose internal antenna gives a few-feet range then drops (physical). BT works only within a couple of feet and cuts out beyond; a U.FL antenna lead popped off the card or none is attached. Fix: reseat the U.FL coax, or use an external USB adapter; keep the device closer as a stopgap. [[https://community.intel.com/t5/Wireless/How-can-I-deal-with-the-extremely-limited-range-of-Bluetooth-in/td-p/692325][intel range]]
- "Software caused connection abort" on connect-after-scan (no). A device with a fine bond aborts with "Software caused connection abort" (err 103) when a scan was stopped just before connecting; stopping discovery races the connection attempt in bluez. Fix: keep discovery running across the connect, or retry without a preceding scan-stop. [[https://github.com/hbldh/bleak/issues/631][bleak 631]]
- A2DP audio stutters whenever a BT mouse is also connected (no). Headset audio skips only while a BT mouse/HID is connected on the same adapter; the two profiles contend for the single controller's scheduling. Fix: switch the audio codec (SBC → SBC-XQ/LDAC) to lower airtime, or move the mouse to a separate dongle; disconnecting the mouse clears it. [[https://bbs.archlinux.org/viewtopic.php?id=279749][arch 279749]]
- BT mouse stutters at ~20 Hz unless a scan is active (no). Mouse motion is choppy but becomes smooth the instant a scan starts; without background inquiry the controller's scheduling starves the HID link. Fix: keep discovery on as a workaround, or apply the connection-parameter fix below. [[https://bbs.archlinux.org/viewtopic.php?id=261632][arch 261632]]
- BLE mouse lag from a too-high negotiated connection interval (yes). A BLE mouse feels laggy because it negotiated a power-saving (long) connection interval and high slave latency. Fix: set =[ConnectionParameters]= (MinInterval=6, MaxInterval=9, Latency=44, Timeout=216) in =/var/lib/bluetooth/<adapter>/<device>/info=, restart bluetooth. [[https://wiki.archlinux.org/title/Bluetooth_mouse][archwiki bt mouse]]

** Bluetooth audio profiles / device classes

Bluetooth-specific audio failures the bt doctor names at its last chain link. The generic PipeWire/WirePlumber internals are owned by [[file:2026-07-10-audio-failure-taxonomy.org][the audio taxonomy]]; these are the ones a bt-panel probe would surface for a connected BT audio device.

- Stale bluez pairing state hides A2DP (yes). Headset connects but only HSP/HFP exist, no A2DP sink. Corrupt/partial pairing records in /var/lib/bluetooth leave A2DP unadvertised. Fix: =rm -rf /var/lib/bluetooth/<adapter>/<dev>=, restart bluetooth, re-pair. [[https://bbs.archlinux.org/viewtopic.php?id=280717][arch 280717]]
- Leftover pulseaudio-bluetooth module steals the endpoint (yes). After moving to PipeWire the device connects but no sink shows. pulseaudio-bluetooth still installed grabs the bluez D-Bus endpoint so pipewire-pulse never creates the card. Fix: =pacman -Rns pulseaudio-bluetooth pulseaudio=, install pipewire-pulse, restart the session. [[https://bbs.archlinux.org/viewtopic.php?id=267690][arch 267690]]
- bluez SPA plugin not installed, no card at all (yes). Device connects at the protocol level but pw-dump shows no bluez node; "api.bluez5.enum.dbus could not be loaded". The libspa bluetooth plugin is missing, so WirePlumber's bluez monitor can't enumerate it. Fix: install the PipeWire bluetooth SPA plugin (libspa-0.2-bluetooth on split distros), restart wireplumber. [[https://bbs.archlinux.org/viewtopic.php?id=304688][arch 304688]]
- WirePlumber seat-monitoring drops the node (no). A connected BT audio device intermittently has no card/node on a non-logind or nested seat. WirePlumber gates node creation on an active logind seat and misfires. Fix: =monitor.bluez.seat-monitoring = disabled= drop-in, restart wireplumber. [[https://pipewire.pages.freedesktop.org/wireplumber/daemon/configuration/bluetooth.html][wp bt config]]
- Autoswitch-to-headset fires on any input stream (no). Music drops to mono phone-call quality whenever any app opens the mic. WirePlumber's =bluetooth.autoswitch-to-headset-profile= flips to HSP/HFP on any capture stream and doesn't switch back. Fix: =wpctl settings --save bluetooth.autoswitch-to-headset-profile false=, or force =a2dp-sink= via set-card-profile. [[https://bbs.archlinux.org/viewtopic.php?pid=1973004][arch 1973004]]
- Codec falls back to SBC, wanted codec never negotiates (no). aptX/LDAC-capable headphones connect but only SBC is active. Default codec order drops to the SBC baseline, or the wanted codec isn't in the allowed set. Fix: =bluez5.codecs = [ ldac aptx_hd aptx aac sbc ]= in a wireplumber drop-in, reconnect. [[https://bbs.archlinux.org/viewtopic.php?id=300230][arch 300230]]
- AAC unavailable because PipeWire lacks fdk-aac (yes). An AAC-only headset never offers AAC and lands on SBC. PipeWire was built without the fdk-aac module (non-free, omitted on some builds). Fix: install libfdk-aac and a PipeWire build with =bluez5-codec-aac= enabled. [[https://bbs.archlinux.org/viewtopic.php?id=289177][arch 289177]]
- LDAC negotiates but adaptive bitrate stays low (no). LDAC is active yet sounds no better than SBC; bitrate never reaches 990k. The default =ldac.quality = auto= collapses to the low tier on a busy 2.4GHz link. Fix: pin =bluez5.a2dp.ldac.quality = "hq"= in a monitor.bluez.rules drop-in, reconnect. [[https://www.guyrutenberg.com/2025/01/09/configuring-ldac-quality-in-pipewire/][guyrutenberg ldac]]
- BT sink not made default, audio stays on laptop speakers (no). Headphones connect but sound keeps coming from the built-in speakers until switched by hand. WirePlumber doesn't promote a freshly-connected BT sink, and the default isn't restored across reconnect. Fix: =wpctl set-default <bt-sink-id>= now; persist with a priority.session bump or default-target restore. [[https://bbs.archlinux.org/viewtopic.php?id=300751][arch 300751]]
- Absolute-volume passthrough makes the slider a no-op (both). The OS volume slider does nothing or only toggles mute/max. AVRCP absolute-volume hands volume to device hardware that only honors 0/100. Fix: =bluez5.enable-hw-volume = false= in a wireplumber drop-in, restart pipewire+wireplumber. [[https://wiki.archlinux.org/title/Bluetooth_headset][archwiki bt headset]]
- Silent sink after suspend/resume despite reconnect (no; the BT-transport view of the audio taxonomy's resume-silence family). After wake the device reconnects but the playing stream is silent; audio returns only on a new track. The resumed transport isn't re-initialized for the existing stream. Fix: =wpctl set-default= to bounce the stream, or disable suspend-on-idle for the node; scripted disconnect/reconnect on resume as a workaround. [[https://forums.linuxmint.com/viewtopic.php?p=2781321][mint 2781321]]
- oFono present blocks native HFP / mSBC (yes; overlaps the audio taxonomy's BT-mic cluster — kept here for the bt-doctor probe). No HFP profile or only CVSD narrowband; mSBC never appears. An installed-but-unconfigured oFono claims the HFP backend so the native backend (which offers mSBC) stays inactive. Fix: remove ofono (or set the native HFP backend), restart pipewire, reconnect. [[https://bbs.archlinux.org/viewtopic.php?id=266252][arch 266252]]
- mSBC wideband unsupported by adapter/kernel (physical). HFP mic works only in muffled narrowband; mSBC never negotiates even on the native backend. mSBC needs adapter+kernel support for USB ALT6 / the transparent SCO path, which some controllers lack. Fix: none in software — use a different adapter, or accept CVSD narrowband. [[https://www.collabora.com/news-and-blog/news-and-events/pipewire-bluetooth-support-status-update.html][collabora bt]]
- HFP profile output dead, mic works (no). In HSP/HFP the mic captures fine but there's no playback through the headset. The native HFP backend's SCO output path fails to route on certain PipeWire versions/devices. Fix: force a2dp-sink for playback and only enter HFP for the call; try switching the HFP backend or a PipeWire version without the regression. [[https://discussion.fedoraproject.org/t/no-audio-output-with-bluetooth-headset-in-hsp-hfp-profile-mic-works-output-doesn-t/155135][fedora hfp-output]]
- Device seen as LE/GATT-only, no audio class (yes). A headset connects but is treated as a data/LE device with no A2DP sink. bluez brings it up over LE (GATT only) instead of Classic/BR-EDR. Fix: =DisableLE= (or =ControllerMode = bredr=) in main.conf, restart bluetooth, remove and re-pair. [[https://bbs.archlinux.org/viewtopic.php?id=303288][arch 303288]]
- Battery percent never reported (yes). =bluetoothctl info= shows no Battery line and the tray shows no BT battery. bluez's battery provider is gated behind experimental mode. Fix: =Experimental = true= under [General] in main.conf, restart bluetooth, reconnect (the device must expose the Battery Service). [[https://github.com/bluez/bluez/issues/362][bluez 362]]
- Multi-device: first-connected BT audio wins, wrong default (no). Two BT audio devices paired; audio always goes to whichever connected first and the other can't be made default cleanly. WirePlumber keeps the earlier sink as default. Fix: =wpctl set-default <desired-sink-id>=; give the preferred device a higher priority.session via a monitor.bluez.rules match. [[https://0110.be/posts/Connecting_two_Bluetooth_headsets_to_your_Linux_system:_audio_routing_in_PipeWire][0110.be dual bt]]
- HFP narrowband mic during calls is an expected tradeoff (no; GUIDE). Opening the mic (calls/meetings) tanks playback to tinny mono. Inherent to HFP/HSP sharing one low-bandwidth SCO link for bidirectional audio; A2DP has no mic path. Fix: none to repair — keep A2DP for listening, accept HFP for calls, or use a duplex codec (FastStream / aptX-LL) that carries the mic without leaving A2DP. [[https://webcodr.io/2024/10/fixing-no-a2dp-with-bluetooth-headsets-on-linux/][webcodr a2dp]]

* Network triage

The ~74 network failure modes sorted into eight symptom clusters, each owned by a tier the net doctor already probes (link → IP → route → DNS → egress), plus a control-plane cluster for NetworkManager itself and a drops cluster for intermittent faults. Every entry carries a remedy class, using the audio taxonomy's four:

- *AUTO* — user-scope, reversible, no root. For net this is the nmcli surface the doctor already drives (bounce/reset, =con modify= for dns/mtu/ipv6/mac/autoconnect, tunnel-down, portal-open) plus user-service restarts. Polkit on an active session (or passwordless sudo on an archsetup install) covers these.
- *PRIV* — needs root: =systemctl restart NetworkManager/systemd-resolved=, editing =/etc/=, installing a firmware/driver package, a modprobe option. Runs silently where passwordless sudo exists, else Confirm/Arm.
- *REBOOT-TAIL* — the runnable part (often PRIV: firmware/driver install, initramfs rebuild, kernel change, a modprobe option) then the reboot the doctor instructs but can't verify past.
- *GUIDE* — nothing to run: the user must supply a secret/cert, flip a physical switch, change a BIOS setting, make a config trade-off, or wait out a venue/ISP outage.

Rough distribution: ~30 AUTO, ~14 PRIV, ~12 REBOOT-TAIL, ~24 GUIDE (several are AUTO-now-plus-PRIV-to-persist, or AUTO-plus-GUIDE where the fix is a decision). The buildable share (AUTO plus the runnable part of PRIV/REBOOT-TAIL) is a little over half — the same shape as audio. Triage is a proposal; correct any class.

Two structural notes carried from the audio design. First, the clusters map onto the probe ladder, so the fix/guide boundary falls along tiers the doctor already walks — cluster N is "the fault the Nth probe step catches". Second, the AUTO core is a handful of primitives (bounce/reset, an nmcli-setter, tunnel-down, a user-service restart, portal-open); the breadth is in the *diagnosis*, not the remedies — exactly as the audio doctor's ~50 diagnoses collapsed to five remedy primitives.

** Cluster 1 — no link (radio/carrier down)
Probe: the link step (=_step_link=: rfkill, has-wifi-device, carrier). New work: a dmesg firmware-load hint would let the doctor name the specific blob (iwlwifi/rtw89/mt7921) rather than a generic "no adapter".

- Wifi soft-blocked by rfkill :: AUTO — =rfkill unblock wifi= / =nmcli radio wifi on= (the doctor's rfkill repair).
- Wifi hard-blocked by a physical switch / BIOS :: GUIDE — flip the switch or enable in BIOS.
- rfkill stuck hard-blocked after suspend (WMI conflict) :: REBOOT-TAIL — blacklist the wrong WMI module, rebuild initramfs, reboot.
- Missing iwlwifi/mt7921/rtw89 firmware for a new card :: REBOOT-TAIL — install/update linux-firmware (PRIV), reboot.
- Firmware-load regression after a kernel/firmware update :: REBOOT-TAIL — boot linux-lts or pin the last-good firmware, reboot.
- Realtek rtw89 shadowed by an AUR DKMS driver :: REBOOT-TAIL — remove the DKMS package, reboot.
- Broadcom BCM4360 needs the wl driver / wl breaks after a kernel upgrade :: REBOOT-TAIL — install broadcom-wl-dkms, blacklist the open drivers, reboot.
- USB wifi dongle needs an out-of-tree DKMS driver :: REBOOT-TAIL — install the DKMS package, reboot.
- Ethernet NO-CARRIER (cable/switch) :: GUIDE — reseat/replace the cable, try another port.
- RTL8125 flips to r8169 after a kernel update :: REBOOT-TAIL — blacklist r8169, install r8125-dkms, reboot.
- RTL8125 downshifts / won't negotiate speed :: PRIV — =ethtool --set-eee eee off= (GUIDE the cable/switch swap).
- Adapter left "unmanaged" by NetworkManager :: AUTO + PRIV — =nmcli device set managed yes= (AUTO); remove the config rule / disable the rival manager to persist (PRIV). Also lives in cluster 7.

** Cluster 2 — associated but no IP
Probe: the DHCP step (=_step_dhcp=). New work: distinguish "no DHCP answer" (server-side) from "conflict/ACD refused" (a duplicate on the LAN) so the message points the right way.

- dhcpcd competing with NM's internal client :: PRIV — =systemctl disable --now dhcpcd=. Also cluster 7.
- dhcpcd 9 backend breaks NM IPv4 :: PRIV — =dhcp=internal= in NetworkManager.conf.
- APIPA / no DHCP answer :: AUTO — re-trigger DHCP (=nmcli device reapply=); a recurrence is server-side (GUIDE).
- Duplicate IPv4, address skipped by ACD :: GUIDE — change the conflicting host/reservation (a network decision).
- IPv6 RA not received, no SLAAC :: PRIV — =sysctl accept_ra=2= (or GUIDE the router RA-guard).
- DHCPv6-only network, address but no route :: GUIDE — the router must send an RA with the M flag; =ipv6.method auto= is AUTO but the fix is router-side.

** Cluster 3 — have IP, no route to the internet
Probe: gateway + route + VPN-policy steps (=_step_gateway=, =_step_route=, =_vpn_policy_signal=). This is where the doctor's tunnel-down repair and the "VPN owns the route" terminal case live.

- Default route never installed (=never-default=) :: AUTO — =nmcli con modify never-default no=, up.
- DHCP gateway off the lease's subnet :: PRIV — add the on-link route then default (GUIDE the DHCP-scope fix).
- Wifi+ethernet conflicting metrics, exits the dead link :: AUTO — raise the bad link's =ipv4.route-metric=.
- WireGuard AllowedIPs=0.0.0.0/0 strands the host :: AUTO — bring the tunnel down (the doctor's tunnel-down repair).
- WireGuard split-tunnel captures the LAN :: GUIDE — fix AllowedIPs (a config decision).
- OpenVPN redirect-gateway route left behind :: PRIV — flush the stale route, restart the client.
- Tailscale exit node captures the default route :: AUTO — =tailscale set --exit-node==.
- Docker bridge / libvirt virbr0 subnet collision :: PRIV — re-address the bridge (a config decision, GUIDE-adjacent).

** Cluster 4 — authentication rejected (mostly terminal)
Probe: NM state 120 + GENERAL.REASON + the journal tail (the doctor's =_recent_auth_failure=). This is the cluster the classifier already marks TERMINAL and refuses to loop repairs on — the fix is almost always the user supplying a correct secret or cert.

- Wrong PSK, NM state 120 :: GUIDE (TERMINAL) — the user re-enters the key; no repair fixes it.
- Pure WPA3-SAE won't associate :: AUTO — set =key-mgmt sae= + PMF on the profile.
- PMF mismatch on a transition AP :: AUTO — match the AP's =pmf=.
- SAE H2E-only vs hunt-and-peck :: PRIV — =sae_pwe=2= in wpa_supplicant config.
- eduroam/enterprise cert validation failed (PEAP/iwd/802.1X/anon-identity) :: GUIDE — supply the correct CA cert / server-name / realm; the doctor can't invent institutional certs.
- Hidden SSID never connects :: AUTO — =wifi.hidden yes= on the profile.
- Randomized MAC breaks a portal / allow-list :: AUTO — =cloned-mac-address stable= (or =permanent=).
- scan-rand-mac-address breaks scan/assoc :: PRIV — a =wifi.scan-rand-mac-address=no= drop-in.
- Wrong regulatory domain hides channels :: PRIV — =iw reg set=, persist via wireless-regdom.
- Won't roam, stuck on a weak AP :: AUTO — bounce the connection (GUIDE the bgscan/backend tuning).
- 4-way-handshake timeout / deauth loop :: REBOOT-TAIL — =11n_disable=1= modprobe option, reboot.

** Cluster 5 — route works, names don't
Probe: dns-config + resolver-health + dns-resolve + the doctor's dns-test (which proves venue-resolver-broken vs egress-dead) and its dns-override/revert repair.

- Dangling resolv.conf symlink / resolv.conf not at the stub :: PRIV — enable resolved or repoint the symlink.
- resolved stub unreachable / port-53 conflict :: PRIV — stop the conflicting resolver, restart resolved.
- NM not integrated with resolved :: PRIV — =dns=systemd-resolved= in NetworkManager.conf.
- DNSSEC rejects a venue resolver / sticky no-signature verdict :: PRIV — =DNSSEC=allow-downgrade= (=resolvectl reset-server-features= is AUTO for the sticky case). GUIDE the trade-off decision.
- DoT strict with 853 blocked / unreachable server :: PRIV — =DNSOverTLS=opportunistic=. GUIDE the trade-off.
- DHCP handed a broken resolver / pinned public DNS blocked :: AUTO — the doctor's dns-override (switch to working DNS) / drop the pin.
- Stale poisoned cache after a portal login :: AUTO — =resolvectl flush-caches=.
- VPN split-DNS not applied :: AUTO — =resolvectl domain/default-route= on the VPN link.
- IPv6 AAAA lookups stall :: AUTO — disable IPv6 on the link (or the single-request option). Also cluster 8.
- Another daemon overwrites resolv.conf :: PRIV — pick one manager, point resolv.conf at the stub.
- nsswitch.conf hosts line / avahi mDNS broken :: PRIV — fix the hosts line, install nss-mdns.

** Cluster 6 — names resolve, egress blocked
Probe: the http/egress-edges steps + the terminal upstream outcome. This is the cluster where the doctor most often must STOP and say "not locally fixable" rather than loop repairs.

- Captive portal held state / no auto-popup / HTTPS-check miss / HSTS block :: AUTO — the doctor's portal-open (load a plain-HTTP probe); PRIV to fix NM's connectivity URI to http.
- Custom DNS/DoT hides the captive portal :: AUTO + PRIV — drop DoT/DNSSEC for the network, log in, restore.
- PMTUD blackhole / PPPoE-VPN MTU not clamped :: AUTO — the doctor's mtu-test then mtu-override (lower the interface MTU).
- Stale http_proxy env / unreachable PAC :: AUTO — clear the proxy env / set system proxy to None.
- Clock skew breaks TLS :: PRIV — the doctor's clock-sync (=timedatectl set-ntp true=); GUIDE the CMOS-battery replacement.
- Firewall default-deny / VPN kill-switch leftover rule :: PRIV — allow egress / flush the stale rule.
- IPv6 egress broken while IPv4 works :: AUTO — disable IPv6 on the connection. Also cluster 8.
- False "limited connectivity" from a local DNS/VPN :: PRIV — fix NM's connectivity URI (AUTO to disable the check). Also cluster 7.
- ISP outage / modem in a bad state :: GUIDE (TERMINAL) — power-cycle the modem, contact the ISP; the doctor recognizes and stops.
- Specific outbound port blocked :: GUIDE — use an allowed alternate or switch networks; not host-fixable.

** Cluster 7 — control plane broken (NetworkManager itself)
Probe: process/service state + config checks. New work: a "two managers fighting" detector (dhcpcd / systemd-networkd / iwd co-active with NM) and a keyfile-permission check, since these fail silently with a healthy-looking radio.

- NM masked / failed to start :: PRIV — =systemctl unmask && start=; reinstall if corrupt.
- NM segfaults / restart-loops :: PRIV — coredump triage, update/downgrade the package.
- iwd + wpa_supplicant both active / backend mismatch / iwd configured-not-installed :: REBOOT-TAIL — pick one backend, disable the other, reboot.
- systemd-networkd + NM both managing the link :: REBOOT-TAIL — disable networkd, reboot.
- Keyfile permissions void a saved connection :: PRIV — =chmod 600=, =chown root=, reload.
- Autoconnect disabled :: AUTO — =connection.autoconnect yes=.
- Duplicate/conflicting profiles for one SSID :: AUTO — delete the stale profile / raise the good one's priority.
- Dispatcher script errors and blocks connectivity :: PRIV — fix ownership or remove the script.
- Polkit won't authorize a non-root user :: GUIDE — start a polkit agent / relogin for an active seat session.
- NetworkManager-wait-online hangs boot :: PRIV — disable the wait-online service.

** Cluster 8 — flaky / drops / powersave
Probe: over-time / event-log signals (the panel's eventlog) plus a re-probe-after-idle check — the least-developed tier, the net analogue of the audio "works then dies" cluster. New work: correlate drop events with powersave/roam/suspend transitions.

- WiFi powersave drops the connection :: AUTO — =iw set power_save off= now; PRIV to persist the NM/modprobe setting.
- USB wifi dongle killed by autosuspend :: PRIV — a udev =power/control=on= rule.
- iwlwifi/ath11k firmware crashloop on resume :: PRIV — reload the module (a sleep hook to persist).
- No reconnect after suspend/resume :: AUTO — the doctor's nm-restart; PRIV for a durable sleep hook.
- IPv6 happy-eyeballs stalls :: AUTO — disable IPv6 on the link. Shared with clusters 5/6 — same broken-v6 family, three probe points (route absent, egress black-holed, AAAA unanswered).

* Bluetooth triage

The ~55 bluetooth failure modes sorted into five symptom clusters, each owned by a link in the bt doctor's existing chain (adapter → rfkill/service/powered → per-device → audio). Same four remedy classes. The bt doctor's design already encodes a key constraint that shapes this triage: *connecting and pairing are user intents, not health repairs* — so the doctor never auto-connects or auto-pairs, and the destructive re-pair is always user-confirmed. That pushes clusters 3 and 4 heavily toward GUIDE and user-initiated actions, with far fewer silent AUTO fixes than the net side.

Rough distribution: ~12 AUTO, ~16 PRIV, ~12 REBOOT-TAIL, ~15 GUIDE. The buildable share is lower than net's because the adapter/firmware cluster is almost entirely PRIV/REBOOT-TAIL/GUIDE and the pairing cluster is mostly user-driven. The doctor's existing safe-auto tiers (unblock, power-on, service-restart, a2dp) all live in clusters 2 and 5 — which is exactly where the buildable share concentrates.

** Cluster 1 — no adapter
Probe: the adapter step (=btctl.show=). New work: a dmesg firmware-load hint would name the vendor blob (ibt-*.sfi, BT_RAM_CODE_MT7961, rtl8761, QCA, BCM .hcd) instead of a generic "no adapter found" — the direct parallel to the audio cluster-1 dmesg-hint proposal.

- btusb not auto-loaded :: PRIV — =modprobe btusb=, persist via modules-load.d.
- Intel/MediaTek/Realtek/Qualcomm/Broadcom firmware missing or mismatched :: REBOOT-TAIL — update linux-firmware or symlink/decompress the requested blob (PRIV), reboot.
- Intel "failed to send firmware data" / broken-initial-NCMD :: REBOOT-TAIL — =btusb reset=1= or a newer kernel, reboot.
- Controller lost after a kernel update (Intel AX / MT7922 / QCA) :: REBOOT-TAIL — boot linux-lts or downgrade, reboot.
- MediaTek MT7922 stuck in a residual power state :: GUIDE — full power-off, pull power ~10s, cold boot.
- Realtek/Broadcom dongle needs an out-of-tree driver or .hcd :: REBOOT-TAIL — build the DKMS driver / install the firmware, reboot.
- Fake CSR clone resets/times out :: PRIV — the kernel clone quirks or =btusb reset=1=, reload.
- MT7925 killed by USB autosuspend :: REBOOT-TAIL — =btusb.enable_autosuspend=n= on the cmdline, reboot. Also cluster 4.
- Bluetooth hard-blocked by BIOS/switch :: GUIDE — flip the switch / enable in BIOS.

** Cluster 2 — adapter blocked, unpowered, or the daemon is down
Probe: the rfkill + service + powered steps. This is where all four of the doctor's safe auto-repairs (unblock, service-restart, power-on) live.

- Soft-blocked adapter :: AUTO — the doctor's unblock (=rfkill unblock bluetooth=).
- Airplane / physical hard-block :: GUIDE — turn airplane mode off / flip the switch (the doctor deliberately won't touch this radio).
- AutoEnable off, powered down every boot :: PRIV — =AutoEnable=true= in main.conf.
- bluetooth.service masked / not enabled :: PRIV — =systemctl unmask / enable --now= (service-restart is the AUTO tier for a stopped-but-enabled service).
- D-Bus policy blocks org.bluez / bad unit-file after a bluez upgrade :: PRIV — reinstall bluez / reconcile the .pacnew, daemon-reload.
- WiFi rfkill toggle also killed BT (combo chip) :: AUTO — the doctor's unblock.
- TLP disables BT on startup / systemd-rfkill restores a stale block :: PRIV — remove BT from the TLP list / clear the saved rfkill state (unblock is AUTO now).
- rfkill block spins bluetoothd at 100% CPU :: AUTO — service-restart after unblock.
- Adapter powers back off after a desktop toggle :: AUTO — unblock + power-on (or re-enable from the desktop).
- BT stuck/soft-blocked on resume, needs a module reload :: PRIV — reload btusb (a sleep hook to persist). Also cluster 4.
- Wrong/missing default controller (multiple adapters) :: AUTO — =bluetoothctl select <MAC>= then power-on.

** Cluster 3 — won't pair / bond
Probe: none in-chain — pairing is a user intent the panel offers, not something the doctor health-repairs. The doctor's one destructive tier here (re-pair = remove + pair) is always user-confirmed, never chained. New work: a "stale bond / corrupt cache" signature (a device that fails auth repeatedly with a bond present) would let the doctor *offer* the re-pair with confidence rather than guess.

- Generic AuthenticationFailed / re-pair loop / corrupt cache survives remove :: PRIV (user-confirmed) — stop bluetooth, =rm -rf= the stale =/var/lib/bluetooth/<adapter>/<mac>=, restart, re-pair.
- Stale link key after a dual-boot re-pair :: GUIDE — remove and re-pair (or sync keys between OSes); a user decision.
- Paired but not trusted, no auto-reconnect :: AUTO — =bluetoothctl trust <mac>= (a safe, non-connecting fix). Bridges to cluster 4.
- No default pairing agent :: GUIDE — register an agent (=agent on=); mostly a headless-setup concern.
- BLE device never appears in scan / not in pairing mode / adapter not pairable :: GUIDE — enable LE transport / put the device in pairing mode / =pairable on= — user actions.
- ConnectionAttemptFailed / page-timeout after a bluez upgrade :: PRIV — restart bluetooth; downgrade bluez if it recurs.
- Headset un-pairs itself on disconnect / BLE address rotates :: GUIDE — re-pair; a device-behavior limitation.
- Legacy keyboard needs the PIN typed on-device :: GUIDE — type the passkey on the keyboard.
- Too many bonded devices, keys lost :: PRIV (user-confirmed) — remove devices below the ~14 limit, restart.
- Dual-mode device pairs on the wrong transport / seen as LE-only :: PRIV — =ControllerMode = bredr= in main.conf, restart, re-pair. Shared with cluster 5.
- Paired without a bond via blueman :: GUIDE — re-pair with =bluetoothctl pair= (which bonds).

** Cluster 4 — paired but the link won't hold
Probe: the per-device connected-state step. A disconnected paired device is information, not a failure; reconnecting is user-initiated. New work: connection-parameter / coexistence hints (name USB3 noise, 2.4GHz coexistence, or a too-aggressive supervision timeout) so a "keeps dropping" verdict points somewhere.

- Paired+trusted device never reconnects on boot/resume :: PRIV — install bluetooth-autoconnect, or set =ReconnectIntervals= in main.conf.
- Xbox/PS controller drops unless ERTM is off :: REBOOT-TAIL — =disable_ertm=1= modprobe option, reboot.
- USB3 port radio noise / loose antenna / short range :: GUIDE — move the device off the USB3 port, reseat the antenna, close the distance.
- WiFi/BT 2.4GHz coexistence stutter :: PRIV — move WiFi to 5GHz / tune the coexistence modprobe option (GUIDE the band move).
- btusb autosuspend input lag / adapter dead after resume :: REBOOT-TAIL — =btusb.enable_autosuspend=0= on the cmdline (PRIV sleep hook for the resume case). Shared with clusters 1/2.
- BLE supervision-timeout / connection-interval too aggressive :: PRIV — raise the timeout / set =[ConnectionParameters]= (a startup service to persist debugfs).
- RTL8761B wrong-firmware reconnect loop :: PRIV — symlink the correct blob, reload. Same cause as cluster 1's name-mismatch.
- "Software caused connection abort" on connect-after-scan :: AUTO — retry the connect without a preceding scan-stop.
- A2DP stutters with a BT mouse also connected / mouse stutters without a scan :: GUIDE — lower audio-codec airtime or move the mouse to a dongle; a contention trade-off.

** Cluster 5 — connected but audio is wrong
Probe: the audio-profile step (=audio.pw_dump=, card/sink for the device). The doctor's a2dp repair (force the A2DP profile) is the AUTO tier here. The generic sound-server internals belong to the audio taxonomy; these are the BT-specific ones the bt panel names.

- No A2DP sink / stale bluez state hides A2DP :: PRIV (user-confirmed) — clear the stale =/var/lib/bluetooth= record, re-pair (the a2dp repair is AUTO when the card is merely on the wrong profile).
- Stuck in HSP/HFP, autoswitch-to-headset fired :: AUTO — the doctor's a2dp repair / disable autoswitch.
- Leftover pulseaudio-bluetooth steals the endpoint / bluez SPA plugin missing :: PRIV — remove pulseaudio-bluetooth / install the SPA plugin.
- WirePlumber seat-monitoring drops the node :: PRIV — a =seat-monitoring = disabled= drop-in.
- Codec falls back to SBC / LDAC stuck low / AAC missing :: AUTO — a =bluez5.codecs= / ldac-quality drop-in (PRIV/REBOOT for the fdk-aac rebuild).
- BT sink not made default :: AUTO — =wpctl set-default= (the audio taxonomy's set-default primitive).
- Absolute-volume slider no-op :: PRIV — =enable-hw-volume = false= drop-in.
- Silent sink after resume :: AUTO — bounce the stream via set-default.
- oFono blocks native HFP / mSBC :: PRIV — remove ofono / set the native backend.
- mSBC unsupported by adapter / HFP output dead :: GUIDE — a hardware or PipeWire-version limitation.
- Device seen as LE/GATT-only, no audio class :: PRIV — =ControllerMode = bredr=, re-pair. Shared with cluster 3.
- Battery percent never reported :: PRIV — =Experimental = true= in main.conf.
- Multi-device, wrong audio default :: AUTO — =wpctl set-default= / a priority.session rule.
- HFP narrowband mic during calls :: GUIDE — an inherent A2DP/HFP trade-off.

* Saturation test

Deferred to a later pass, mirroring the audio taxonomy's blind-different-axis resample. When run, it must sample on a *different* axis than this by-layer first sweep — by hardware vendor, by distro, by device class (headset vs mouse vs controller vs enterprise-wifi vs VPN), weighted toward non-Arch 2024-2026 sources — and run the agents blind to these clusters, so it tests whether the eight net / five bt clusters are representative rather than re-deriving them. The audio resample forced zero new clusters from 108 fresh reports; the expectation here is the same, but it is unproven until run.