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Date:   Sun, 22 Dec 2019 23:10:59 +0100
From:   Guillaume Nault <>
To:     Hangbin Liu <>
Cc:, Julian Anastasov <>,
        Marcelo Ricardo Leitner <>,
        David Ahern <>,
        Eric Dumazet <>,
        David Miller <>,
        Pablo Neira <>,
        Stephen Hemminger <>,
        Alexey Kodanev <>
Subject: Re: [PATCHv5 net 0/8] disable neigh update for tunnels during pmtu

On Sun, Dec 22, 2019 at 10:51:08AM +0800, Hangbin Liu wrote:
> When we setup a pair of gretap, ping each other and create neighbour cache.
> Then delete and recreate one side. We will never be able to ping6 to the new
> created gretap.
> The reason is when we ping6 remote via gretap, we will call like
> gre_tap_xmit()
>  - ip_tunnel_xmit()
>    - tnl_update_pmtu()
>      - skb_dst_update_pmtu()
>        - ip6_rt_update_pmtu()
>          - __ip6_rt_update_pmtu()
>            - dst_confirm_neigh()
>              - ip6_confirm_neigh()
>                - __ipv6_confirm_neigh()
>                  - n->confirmed = now
> As the confirmed time updated, in neigh_timer_handler() the check for
> NUD_DELAY confirm time will pass and the neigh state will back to
> NUD_REACHABLE. So the old/wrong mac address will be used again.
> If we do not update the confirmed time, the neigh state will go to
> neigh->nud_state = NUD_PROBE; then go to NUD_FAILED and re-create the
> neigh later, which is what IPv4 does.
> We couldn't remove the ip6_confirm_neigh() directly as we still need it
> for TCP flows. To fix it, we have to pass a bool parameter to
> dst_ops.update_pmtu() and only disable neighbor update for tunnels.
No more objection from me (and you already have my Reviewed-by tag).
Thanks for your work Hangbin.

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