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Subject: Re: [PATCH net v2 RESEND] ipv6: Reflect MTU changes on PMTU of
 exceptions for MTU-less routes
To: Stefano Brivio <sbrivio@redhat.com>,
        "David S . Miller" <davem@davemloft.net>
Cc: Wei Wang <weiwan@google.com>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        =?UTF-8?Q?Maciej_=c5=bbenczykowski?= <maze@google.com>,
        Xiumei Mu <xmu@redhat.com>, netdev@vger.kernel.org
References: <20180306101019.74424-1-sbrivio@redhat.com>
From: David Ahern <dsahern@gmail.com>
Message-ID: <3f248c84-9c5a-be26-25e9-455024ac3c54@gmail.com>
Date: Tue, 6 Mar 2018 13:30:05 -0700
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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'