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Subject: RE: [PATCH dpdk] net: ipv6 link local compliance with rfc 4291
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Stephen Hemminger" <stephen@networkplumber.org>,
 "Robin Jarry" <rjarry@redhat.com>
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> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Friday, 14 November 2025 17.06
>=20
> On Fri, 14 Nov 2025 11:57:53 +0100
> Robin Jarry <rjarry@redhat.com> wrote:
>=20
> > diff --git a/app/test/test_net_ip6.c b/app/test/test_net_ip6.c
> > index cfc550940306..e4642c9a39d9 100644
> > --- a/app/test/test_net_ip6.c
> > +++ b/app/test/test_net_ip6.c
> > @@ -160,7 +160,7 @@ test_ipv6_llocal_from_ethernet(void)
> >  {
> >  	const struct rte_ether_addr local_mac =3D {{0x04, 0x7b, 0xcb, =
0x5c,
> 0x08, 0x44}};
> >  	const struct rte_ipv6_addr local_ip =3D
> > -		RTE_IPV6(0xfe80, 0, 0, 0, 0x047b, 0xcbff, 0xfe5c, 0x0844);
> > +		RTE_IPV6(0xfe80, 0, 0, 0, 0x067b, 0xcbff, 0xfe5c, 0x0844);
> >  	struct rte_ipv6_addr ip;
>=20
> 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?

>=20
> Perhaps DPDK should roll port id into link local address?