Re: [PATCH] net/ipv6: allow device-only routes via the multipath API

[azey]

On 2025-11-18 10:05:55, +0100 Nicolas Dichtel wrote:
> If I remember well, it was to avoid merging connected routes to ECMP routes.
> For example, fe80:: but also if two interfaces have an address in the same
> prefix. With the current code, the last route will always be used. With this
> patch, packets will be distributed across the two interfaces, right?
> If yes, it may cause regression on some setups.

Thanks! Yes, with this patch routes with the same destination and metric automatically
become multipath. From my testing, for link-locals this shouldn't make a difference
as the interface must always be specified with % anyway.

For non-LL addresses, this could indeed cause a regression in obscure setups. In my
opinion though, I feel that it is very unlikely anyone who has two routes with the
same prefix and metric (which AFAIK, isn't really a supported configuration without
ECMP anyway) relies on this quirk. The most plausible setup relying on this I can
think of would be a server with two interfaces on the same L2 segment, and a
firewall somewhere that only allows the source address of one interface through.

IMO, setups like that are more of a misconfiguration than a "practical use case"
that'd make this a real regression, but I'd completely understand if it'd be enough
to block this.