netdev - Re: Question about linux kernel commit: "net/ipv6: move metrics from dst to rt6

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Date:   Wed, 10 Jul 2019 21:09:54 +0200
From:   Stefano Brivio <sbrivio@...hat.com>
To:     Jan Szewczyk <jan.szewczyk@...csson.com>
Cc:     David Ahern <dsahern@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Wei Wang <weiwan@...gle.com>, Martin KaFai Lau <kafai@...com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: Question about linux kernel commit: "net/ipv6: move metrics
 from dst to rt6_info"

Jan,

On Wed, 10 Jul 2019 12:59:41 +0000
Jan Szewczyk <jan.szewczyk@...csson.com> wrote:

> Hi!
> I digged up a little further and maybe it's not a problem with MTU
> itself. I checked every entry I get from RTM_GETROUTE netlink message
> and after triggering "too big packet" by pinging ipv6address I get
> exactly the same messages on 4.12 and 4.18, except that the one with
> that pinged ipv6address is missing on 4.18 at all. What is weird -
> it's visible when running "ip route get to ipv6address". Do you know
> why there is a mismatch there?

If I understand you correctly, an implementation equivalent to 'ip -6
route list show' (using the NLM_F_DUMP flag) won't show the so-called
route exception, while 'ip -6 route get' shows it.

If that's the case: that was broken by commit 2b760fcf5cfb ("ipv6: hook
up exception table to store dst cache") that landed in 4.15, and fixed
by net-next commit 1e47b4837f3b ("ipv6: Dump route exceptions if
requested"). For more details, see the log of this commit itself.

-- 
Stefano