[PATCH] Netlink: Propagate ecmp nexthop weight to kernel for inet6 routes

[Ondrej Zajicek]

On Sun, May 22, 2022 at 10:28:12PM +0200, dxld at darkboxed.org wrote:
> After looking at this more I realise now how bird is splitting multiple
> ipv6 nexthops into sequences of route updates for the same prefix.
> 
> Consequently the code doing this should also be removed. Though it seems it
> works just fine either way but I get errors for the (now redundant) route
> removals.
> 
> Are we even OK with raising the kernel version required or should I try to
> preserve support for the old kernel interface?

Hi

The initial IPv6 multipath support required several ugly hacks in Netlink
code, which i would be happy to get rid of. When Linux came with IPv6
RTA_MULTIPATH support, the initial versions were somewhat buggy, so we
kept using the old API for updates (splitting multipath routes to
sequences of route updates), while accepting RTA_MULTIPATH routes in
scans / notifications. My notes say that minimal reliable kernel version
for IPv6 RTA_MULTIPATH is 4.11.

As a rule of thumb, i target compatibility for ~5 year old systems that
are not EOL, for example Debian LTS. Current Debian LTS is Debian 9
(Stretch), which uses kernel 4.9, but it will be EOL in a ~month, while
Debian 10 uses kernel 4.19. For kernel itself, ~5 year old LTS release
would be 4.14.

So i would be OK with targeting 4.14 / 4.19 as the oldest supported
version and switching completely to RTA_MULTIPATH code in Netlink.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."