netdev - Re: [PATCH net v2 RESEND] ipv6: Reflect MTU changes on PMTU of exceptions for MTU-less routes

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Message-ID: <3f248c84-9c5a-be26-25e9-455024ac3c54@gmail.com>
Date:   Tue, 6 Mar 2018 13:30:05 -0700
From:   David Ahern <dsahern@...il.com>
To:     Stefano Brivio <sbrivio@...hat.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     Wei Wang <weiwan@...gle.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Maciej Żenczykowski <maze@...gle.com>,
        Xiumei Mu <xmu@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net v2 RESEND] ipv6: Reflect MTU changes on PMTU of
 exceptions for MTU-less routes

On 3/6/18 3:10 AM, Stefano Brivio wrote:
> Currently, administrative MTU changes on a given netdevice are
> not reflected on route exceptions for MTU-less routes, with a
> set PMTU value, for that device:
> 
>  # ip -6 route get 2001:db8::b
>  2001:db8::b from :: dev vti_a proto kernel src 2001:db8::a metric 256 pref medium
>  # ping6 -c 1 -q -s10000 2001:db8::b > /dev/null
>  # ip netns exec a ip -6 route get 2001:db8::b
>  2001:db8::b from :: dev vti_a src 2001:db8::a metric 0
>      cache expires 571sec mtu 4926 pref medium
>  # ip link set dev vti_a mtu 3000
>  # ip -6 route get 2001:db8::b
>  2001:db8::b from :: dev vti_a src 2001:db8::a metric 0
>      cache expires 571sec mtu 4926 pref medium
>  # ip link set dev vti_a mtu 9000
>  # ip -6 route get 2001:db8::b
>  2001:db8::b from :: dev vti_a src 2001:db8::a metric 0
>      cache expires 571sec mtu 4926 pref medium

Using your test script, I never see the route get an updated MTU -- it
is always 1426.

++ exception='fd00:2::b from :: dev vti_a src fd00:2::a metric 0 expires
598sec mtu 1426 pref medium'