[tor-relays] Re: If the IPv6 ORPort can't be reached, will clients/relays fall back to the IPv4 ORPort?

["rE-Bo0t.bx1 via tor-relays" <tor-relays@xxxxxxxxxxxxxxxxxxxx>]

Hi forest,

Short answer: no, Tor doesn't do Happy Eyeballs for OR connections. Whatever address family gets picked for a connection attempt is what gets tried, and if it fails, that's it for that attempt. Tor won't turn around and retry the same relay over IPv4. A later circuit attempt may try again or choose another path, but that's separate, not a fallback.

It's a known gap. There's a proposal for it, Prop 306, "IPv6 Happy Eyeballs" [1], but it was never implemented and is still open.

RST vs silence: an RST or usable ICMPv6 error may make the attempt fail faster, while silently dropped traffic has to wait for a timeout. Either way, there is no fallback for that attempt.

Worth keeping in mind, the DAs reaching the IPv6 ORPort only proves it's reachable from their networks, not from every client or relay out there.

Operationally, if the relay's IPv6 is broken, fix it or stop advertising it. Comment out the explicit IPv6 ORPort line and reload or restart Tor. If IPv6 is still being published, set AddressDisableIPv6 1. That saves clients from hitting a dead end for no reason.

[1] https://spec.torproject.org/proposals/306-ipv6-happy-eyeballs.html

Cheers,
rE-Bo0t.bx1
https://relays.brokenbotnet.com

    On 7/21/26 6:52 AM, forest-relay-contact--- via tor-relays wrote:
> Hello.
>       
>       If a client or relay with IPv6 attempts to connect to a relay's
>       IPv6
>       ORPort and receives no response, will it fall back to IPv4 or will
>       it
>       consider the relay unreachable? Assume that the directory
>       authorities
>       are able to reach the v6 ORPort.
>       
>       Is the behavior different if there is an explicit error returned,
>       e.g.
>       RST or an ICMPv6 no route to host?
>       
>       Regards,
>       forest
>     
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