netdev - Re: IPv6 Router Advertisement Router Preference (RFC 4191) behavior issue

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Message-ID: <ab9b65b4-04d6-0bfe-4fd1-91af9ac5aa0d@gmail.com>
Date:   Sun, 28 Nov 2021 16:11:12 -0700
From:   David Ahern <dsahern@...il.com>
To:     Juhamatti Kuusisaari <juhamatk@...il.com>, netdev@...r.kernel.org
Subject: Re: IPv6 Router Advertisement Router Preference (RFC 4191) behavior
 issue

On 11/18/21 3:35 AM, Juhamatti Kuusisaari wrote:
> Hello,
> 
> I have been testing IPv6 Router Advertisement Default Router
> Preference on 5.1X and it seems it is not honoured by the Linux
> networking stack. Whenever a new default router preference with a
> higher or lower preference value is received, a new default gateway is
> added as an ECMP route in the routing table with equal weight. This is
> a bit surprising as RFC 4191 Sec. 3.2 mentions that the higher
> preference value should be preferred. This part seems to be missing
> from the Linux implementation.
> 
> The problem has existed apparently for a while, see below discussion
> for reference:
> https://serverfault.com/questions/768932/can-linux-be-made-to-honour-ipv6-route-advertisement-preferences
> 
> I am happy to test any improvements to this, in case someone takes a look.
> 

do you have CONFIG_IPV6_ROUTER_PREF enabled and accept_ra_rtr_pref set
for the device?