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

["Robin Jarry" <rjarry@redhat.com>]

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.

https://github.com/jeffmahoney/linux-pre-git/commit/44993d3bb812f
> 2005/01/17 13:13:52-08:00 hch
> [IPV6]: Fix EUI64 generation on S/390.
>
>  - put a dev_id field in struct net_device, so that it uses space that
>    would be wasted by padding otherwise.
>  - if this fields is non-null let ipv6_generate_eui64 use the algorithm
>    from the QETH code to generate an EUI that's different for each
>    OS instance.  See code comments for details.
>
> Signed-off-by: David S. Miller <davem@davemloft.net>

I don't think DPDK should care about this.

-- 
Robin

> Do not use while operating a motor vehicle or heavy machinery.