Re: [PATCH dpdk] net: ipv6 link local compliance with rfc 4291

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 14 Nov 2025 17:46:42 +0100
"Robin Jarry" <rjarry@redhat.com> wrote:

> Morten Brørup, Nov 14, 2025 at 17:14:
> >> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> >> Reading the kernel source there is also special handling to include
> >> device
> >> id into link local address. This is to handle corner case where
> >> multiple network
> >> cards have same hardware MAC address.  
> >
> > Multiple physical NICs should never have the same MAC address.
> > Lots of stuff will break if they do.
> > E.g. a network switch will forward packets to the NIC that most recently sent packets, so its MAC address was learned in the MAC address table in the switch.
> >
> > What is the use case justifying this tweak in the kernel?  
> 
> Some drivers expose multiple ports sharing the same mac address.
> 
> This very is specific to certain hardware vendors. The comment here
> refers to a change from 2005. I couldn't find the root commit/email.

Yes, this code is in first git commit 2.6.12 from 2005 it is possible
(but not worth the effort) to find it in earlier repos.