Re: Default IPv6 gateway outside of an interface subnet, OVH

On 22/07/2026 22:15, Mikolaj Kucharski wrote:

> Hi.
>
> I was using for long the workaround of prefix 56 on an interface to make
> IPv6 work in OVH. I tried today to make on-link setup work, but I fail to
> figure out how, for IPv6.
>
> I'm on -current.
>
> # sysctl -n kern.version
> OpenBSD 8.0-beta (GENERIC.MP) #51: Tue Jul 21 20:50:59 MDT 2026
>      [email protected]:/usr/src/sys/arch/amd64/compile/GENERIC.MP
>
>
> Here is my hostnname.if(5):
>
> ---8<---
> inet xxx.xxx.xxx.aaa/32
> !route -n add -inet -host xxx.xxx.xxx.254 -link -iface \$if
> !route -n add -inet default xxx.xxx.xxx.254
>
> inet6 zzzz:zzzz:zzz:zzdc::1 128
> !route -n add -inet6 -host zzzz:zzzz:zzz:zzff:ff:ff:ff:ff -link -iface \$if
> !route -n add -inet6 default zzzz:zzzz:zzz:zzff:ff:ff:ff:ff
>
> up
> --->8---
>
> Above setup for IPv4 works, but for IPv6 doesn't. Execution looks successful:
>
> # ifconfig ix0 -inet6
> # sh /etc/netstart ix0
> add host xxx.xxx.xxx.254: gateway ix0
> add net default: gateway xxx.xxx.xxx.254
> add host zzzz:zzzz:zzz:zzff:ff:ff:ff:ff: gateway ix0
> add net default: gateway zzzz:zzzz:zzz:zzff:ff:ff:ff:ff
>
> but it doesn't work:
>
> # ping6 -n -c3 zzzz:zzzz:zzz:zzff:ff:ff:ff:ff
> PING zzzz:zzzz:zzz:zzff:ff:ff:ff:ff (zzzz:zzzz:zzz:zzff:ff:ff:ff:ff): 56 data bytes
> ping6: sendmsg: Invalid argument
> ping: wrote zzzz:zzzz:zzz:zzff:ff:ff:ff:ff 64 chars, ret=-1
> ping6: sendmsg: Invalid argument
> ping: wrote zzzz:zzzz:zzz:zzff:ff:ff:ff:ff 64 chars, ret=-1
> ping6: sendmsg: Invalid argument
> ping: wrote zzzz:zzzz:zzz:zzff:ff:ff:ff:ff 64 chars, ret=-1
>
> --- zzzz:zzzz:zzz:zzff:ff:ff:ff:ff ping statistics ---
> 3 packets transmitted, 0 packets received, 100.0% packet loss
>
>
> # ndp -na | grep ff:ff
> zzzz:zzzz:zzz:zzff:ff:ff:ff:ff          (incomplete)          ix0 permanent R
>
>
> What I am missing?
>
> Please CC me with any replies as I'm not subscribed to misc.

 From man route's example:

Add a static inet6(4) route to a host which is on the vio0 interface 
that is outside your prefix, and use that host as a default gateway, as 
used by some hosting providers:

            # route add -inet6 2001:db8:efef::1 -cloning -link -iface vio0
            # route add -inet6 default 2001:db8:efef::1

(thanks to sibiria on #openbsd for finding the right manpage).

Cheers,

Noth