sysctl.conf: Keep IPv6 on lo #603
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With IPv6 disabled on all interfaces, lo has no ::1. But since commit 915614d (sysctl.conf: Allow inet free binds) also sets net.ipv6.ip_nonlocal_bind = 1, binding to ::1 still succeeds, while connecting to it fails: bind ::1 ok connect ::1 failed: [Errno 99] Cannot assign requested address Servers that try ::1 first and fall back to 127.0.0.1 only when the bind fails therefore listen on an address no client can reach. Bazel does exactly that (GrpcServerImpl binds [::1] via Netty's epoll transport), so on MXQ nodes its client never connects to its own server: Starting local Bazel server and connecting to it... ... still trying to connect to local Bazel server (154781) after 10 seconds ... [...] FATAL: couldn't connect to server (154781) after 120 seconds. Re-enable IPv6 on lo only, so ::1 exists. Other interfaces stay without IPv6, as `all` and `default` keep disable_ipv6 = 1. Applying the changed file with `sysctl -p` in a network namespace gives lo ::1/128, and connecting to a server bound to ::1 succeeds. Assisted-by: claude-opus-5 (Claude Code)
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AI disclaimer: This merge/pull request was generated by claude-opus-5 (Claude Code).
With
net.ipv6.conf.all.disable_ipv6 = 1, lo has no::1. But because ofnet.ipv6.ip_nonlocal_bind = 1(commit 915614d (sysctl.conf: Allow inet free binds)), binding to::1still succeeds, while connecting to it fails:Servers trying
::1first, and falling back to 127.0.0.1 only if the bind fails, therefore listen on an address no client can reach. Bazel does exactly that (GrpcServerImplbinds[::1]via Netty’s epoll transport), so on MarIuX the Bazel client never connects to its own server:Re-enable IPv6 on lo only. All other interfaces stay without IPv6, as
allanddefaultkeepdisable_ipv6 = 1.Tested in a network namespace (
unshare -rn): applying the changed file withsysctl -pgives lo::1/128, and connecting to a server bound to::1succeeds.Two related notes (not changed here):
ip6.service’sExecStopwritesall.disable_ipv6 = 1, which would remove::1from lo again./etc/hostshas no::1 localhostentry, sogetent hosts localhostreturns::1from unbound’s built-in localhost zone, whilegetent ahosts localhostreturns 127.0.0.1 from/etc/hosts.