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([2601:282:803:7700:64cc:52f7:7602:a8f2]) by smtp.googlemail.com with ESMTPSA id l31sm11312014qtc.33.2020.07.17.08.04.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Jul 2020 08:04:53 -0700 (PDT) Subject: Re: [PATCH net-next 1/3] udp_tunnel: allow to turn off path mtu discovery on encap sockets To: Stefano Brivio , Florian Westphal Cc: netdev@vger.kernel.org, aconole@redhat.com References: <20200712200705.9796-1-fw@strlen.de> <20200712200705.9796-2-fw@strlen.de> <20200713003813.01f2d5d3@elisabeth> <20200713080413.GL32005@breakpoint.cc> <20200713140219.GM32005@breakpoint.cc> <20200714143327.2d5b8581@redhat.com> <20200715124258.GP32005@breakpoint.cc> <20200715153547.77dbaf82@elisabeth> <20200715143356.GQ32005@breakpoint.cc> <20200717142743.6d05d3ae@elisabeth> From: David Ahern Message-ID: <89e5ec7b-845f-ab23-5043-73e797a29a14@gmail.com> Date: Fri, 17 Jul 2020 09:04:51 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200717142743.6d05d3ae@elisabeth> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 7/17/20 6:27 AM, Stefano Brivio wrote: >> >>> Note that this doesn't work as it is because of a number of reasons >>> (skb doesn't have a dst, pkt_type is not PACKET_HOST), and perhaps we >>> shouldn't be using icmp_send(), but at a glance that looks simpler. >> >> Yes, it also requires that the bridge has IP connectivity >> to reach the inner ip, which might not be the case. > > If the VXLAN endpoint is a port of the bridge, that needs to be the > case, right? Otherwise the VXLAN endpoint can't be reached. > >>> Another slight preference I have towards this idea is that the only >>> known way we can break PMTU discovery right now is by using a bridge, >>> so fixing the problem there looks more future-proof than addressing any >>> kind of tunnel with this problem. I think FoU and GUE would hit the >>> same problem, I don't know about IP tunnels, sticking that selftest >>> snippet to whatever other test in pmtu.sh should tell. >> >> Every type of bridge port that needs to add additional header on egress >> has this problem in the bridge scenario once the peer of the IP tunnel >> signals a PMTU event. > > Yes :( > The vxlan/tunnel device knows it is a bridge port, and it knows it is going to push a udp and ip{v6} header. So why not use that information in setting / updating the MTU? That's what I was getting at on Monday with my comment about lwtunnel_headroom equivalent.