IPv6 prefix is not stored to kernel when multipath is enabled in 1.6.8

[Alexander Zubkov]

Hi,

I think multipath over device routes for ipv6 requires using new nexthop
objects. Here is an example:

# ip link add name a type dummy
# ip link add name b type dummy
# ip link set dev a up
# ip link set dev b up
# ip -6 route add fc00:0::/32 dev a
# ip -6 route add fc00:1::/32 dev b
# ip -6 route add fc00:2::/32 nexthop dev a
Error: Device only routes can not be added for IPv6 using the multipath API.
# ip -6 route add fc00:3::/32 nexthop dev a nexthop dev b
Error: Device only routes can not be added for IPv6 using the multipath API.
# ip -6 nexthop add id 100 dev a
# ip -6 nexthop add id 101 dev b
# ip nexthop add id 102 group 100/101
# ip -6 route add fc00:4::/32 nhid 102
# ip -6 route list
fc00::/32 dev a metric 1024 pref medium
fc00:1::/32 dev b metric 1024 pref medium
fc00:4::/32 nhid 102 metric 1024 pref medium
nexthop dev a weight 1
nexthop dev b weight 1
fe80::/64 dev a proto kernel metric 256 pref medium
fe80::/64 dev b proto kernel metric 256 pref medium
# sysctl -w net.ipv4.nexthop_compat_mode=0
net.ipv4.nexthop_compat_mode = 0
# ip -6 route list
fc00::/32 dev a metric 1024 pref medium
fc00:1::/32 dev b metric 1024 pref medium
fc00:4::/32 nhid 102 metric 1024 pref medium
fe80::/64 dev a proto kernel metric 256 pref medium
fe80::/64 dev b proto kernel metric 256 pref medium
# ip nexthop list
id 100 dev a scope link
id 101 dev b scope link
id 102 group 100/101



On Wed, Feb 19, 2025 at 2:20 PM Ondrej Zajicek <santiago at crfreenet.org>
wrote:

> On Wed, Feb 19, 2025 at 10:39:53AM +0800, Jimmy Lim wrote:
> > Hi Maria,
> >
> > It looks like it doesn't like the configuration of directing IPv6 prefix
> > that we receive from gw (we have 3 sessions) to ifname. The multipath is
> > working fine for IPv6 after I removed that configuration, and it works
> for
> > both bird v1 and v2:
>
> Hi
>
> Yeah, there was some kernel issue rekated to IPv6 multipath direct
> routes. We have some workaround in the code for this case, but likely
> only for the recent versions of BIRD.
>
> --
> Elen sila lumenn' omentielvo
>
> Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
> "To err is human -- to blame it on a computer is even more so."
>
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