RPC wont bind without an IP address on a non-localhost interface #13155

If the only interface which has an IP address and is up is lo, one of the two default rpcbinds (:: and 0.0.0.0) will fail with "libevent: getaddrinfo: address family for nodename not supported".

I know this is an old one, but can you offer steps to reproduce? I down'ed all interfaces except lo on macOS and rpc bound fine:

--> ifconfig | grep UP -A 5
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
	options=1203<RXCSUM,TXCSUM,TXSTATUS,SW_TIMESTAMP>
	inet 127.0.0.1 netmask 0xff000000 
	inet6 ::1 prefixlen 128 
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
	nd6 options=201<PERFORMNUD,DAD>

2023-04-07T17:19:42Z Binding RPC on address ::1 port 18443
2023-04-07T17:19:42Z Binding RPC on address 127.0.0.1 port 18443

However,

I did notice that in a docker container with no ipv6 I got the error you reported... but that makes sense so I don't understand if there is still a bug or if you think the error message maybe needs to be changed?

# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 172.17.0.2  netmask 255.255.0.0  broadcast 172.17.255.255
        ether 02:42:ac:11:00:02  txqueuelen 0  (Ethernet)
        RX packets 195  bytes 218835 (218.8 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 131  bytes 7323 (7.3 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 24  bytes 1200 (1.2 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 24  bytes 1200 (1.2 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

2023-04-07T16:41:56Z Binding RPC on address ::1 port 18443
2023-04-07T16:41:56Z [libevent:warning] getaddrinfo: address family for nodename not supported
2023-04-07T16:41:56Z Binding RPC on address ::1 port 18443 failed.
2023-04-07T16:41:56Z Binding RPC on address 127.0.0.1 port 18443

Thanks Matt! Closing for now, lets reopen if it comes up again

Reopening for now, because it came up again. cc @m3dwards

I believe this is the same issue as in #30245 but in libevent.

If you pass ::1 to getaddrinfo when configured with AI_ADDRCONFIG it will check that there is a non loopback IPV6 interface configured. This was to prevent IPV6 DNS lookups on IPV4 only machines which could be slow.

Please see #30245 for a more full write up and some references.

As I understand it, there are efforts to replace libevent so rather than attempting to get this behaviour changed upstream in libevent we could just wait for that.

one of the two default rpcbinds (:: and 0.0.0.0) will fail

Which one? Is it always :: or always 0.0.0.0 or randomly one or the other? I guess there is some mistake here because the default rpcbinds are ::1 and 127.0.0.1 (not :: and 0.0.0.0).

Noticed this when there is only IPv6 address assigned to eth0 interface (lo has both 127.0.0.1 and ::1). When IPv4 address is also added to eth0, problem disappears.

Bitcoin Core version v29.0.0 (release build)
Using the 'arm_shani(1way,2way)' SHA256 implementation
Startup time: 2025-08-26T21:30:01Z
Default data directory /.bitcoin
Using data directory /ssd/bitcoind/mainnet
Config file: /home/bitcoind/mainnet.conf
Config file arg: chain="main"
Config file arg: datadir="/ssd/bitcoind/mainnet"
Config file arg: disablewallet="1"
Config file arg: discover="1"
Config file arg: externalip="****"
Config file arg: logtimestamps="0"
Config file arg: maxconnections="80"
Config file arg: maxuploadtarget="2048"
Config file arg: onion="127.0.0.1:9050"
Config file arg: printtoconsole="1"
Config file arg: rpcallowip="127.0.0.1"
Config file arg: rpcauth=****
Config file arg: rpcbind="127.0.0.1"
Config file arg: rpcport="8332"
Config file arg: server="1"
Config file arg: whitelist="127.0.0.1"
Config file arg: zmqpubrawblock="tcp://127.0.0.1:8331"
Config file arg: zmqpubrawtx="tcp://127.0.0.1:8330"
Command-line arg: conf="/home/bitcoind/mainnet.conf"
Using at most 80 automatic connections (1024 file descriptors available)
Wallet disabled!
scheduler thread start
Binding RPC on address 127.0.0.1 port 8332
[libevent:warning] getaddrinfo: address family for nodename not supported
Binding RPC on address 127.0.0.1 port 8332 failed.
Unable to bind any endpoint for RPC server
[error] Unable to start HTTP server. See debug log for details.
Shutdown: In progress...
scheduler thread exit
Shutdown: done