linux-kernel - Re: Wrong source address selection in arp

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Message-ID: <t6emma5j63fsaujkxgxpkihap5qena6yp5qhfbr3u7rkgv2brq@loognuyll4ut>
Date: Wed, 22 Oct 2025 10:57:05 +0200
From: Gabriel Goller <g.goller@...xmox.com>
To: Ido Schimmel <idosch@...sch.org>
Cc: davem@...emloft.net, dsahern@...nel.org, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, horms@...nel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: Wrong source address selection in arp_solicit for forwarded
 packets

On 21.10.2025 18:56, Ido Schimmel wrote:
> On Tue, Oct 21, 2025 at 02:31:51PM +0200, Gabriel Goller wrote:
> > Hmm I don't know how this would help? There is a link-local address set
> > on the interface, but we would have to add a ipv6 source address to the
> > arp packet which wouldn't be right?
> 
> There are no ARP packets. Neighbour resolution is performed via IPv6
> NA/NS messages. The script below [1] replicates your setup as I
> understand, but it uses IPv6 link-local addresses for the nexthops.

Ah yes, I understand what you mean now. Still, in an IPv4-only
environment (e.g. OSPFv2, which does not support IPv6, where we would
have to add route-maps [0] for every interface to rewrite the routes)
you still have that problem.

[0]: https://docs.frrouting.org/en/latest/routemap.html#clicmd-set-ip-next-hop-peer-address

> [snip]

Thanks,
Gabriel