From: Stefano Brivio <sbrivio@redhat.com>
To: Florian Westphal <fw@strlen.de>
Cc: <netdev@vger.kernel.org>, aconole@redhat.com
Subject: Re: [PATCH net-next 0/3] vxlan, geneve: allow to turn off PMTU updates on encap socket
Date: Mon, 13 Jul 2020 00:39:33 +0200 [thread overview]
Message-ID: <20200713003933.292755b4@elisabeth> (raw)
In-Reply-To: <20200712200705.9796-1-fw@strlen.de>
On Sun, 12 Jul 2020 22:07:02 +0200
Florian Westphal <fw@strlen.de> wrote:
> There are existing deployments where a vxlan or geneve interface is part
> of a bridge.
>
> In this case, MTU may look like this:
>
> bridge mtu: 1450
> vxlan (bridge port) mtu: 1450
> other bridge ports: 1450
>
> physical link (used by vxlan) mtu: 1500.
>
> This makes sure that vxlan overhead (50 bytes) doesn't bring packets over the
> 1500 MTU of the physical link.
>
> Unfortunately, in some cases, PMTU updates on the encap socket
> can bring such setups into a non-working state: no traffic will pass
> over the vxlan port (physical link) anymore.
> Because of the bridge-based usage of the vxlan interface, the original
> sender never learns of the change in path mtu and TCP clients will retransmit
> the over-sized packets until timeout.
>
>
> When this happens, a 'ip route flush cache' in the netns holding
> the vxlan interface resolves the problem, i.e. the network is capable
> of transporting the packets and the PMTU update is bogus.
>
> Another workaround is to enable 'net.ipv4.tcp_mtu_probing'.
>
> This patch series allows to configure vxlan and geneve interfaces
> to ignore path mtu updates.
Regardless of the comments to 1/3, I don't have any problem with this
(didn't review yet) if it's the only way to currently work around the
issue (of course :)).
I think we should eventually fix PMTU discovery for bridged setups, but
perhaps it's more complicated than that.
I wonder, though:
- wouldn't setting /proc/sys/net/ipv4/ip_no_pmtu_disc have the same
effect?
- does it really make sense to have this configurable for IPv6?
--
Stefano
prev parent reply other threads:[~2020-07-12 22:39 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-12 20:07 [PATCH net-next 0/3] vxlan, geneve: allow to turn off PMTU updates on encap socket Florian Westphal
2020-07-12 20:07 ` [PATCH net-next 1/3] udp_tunnel: allow to turn off path mtu discovery on encap sockets Florian Westphal
2020-07-12 22:38 ` Stefano Brivio
2020-07-13 8:04 ` Florian Westphal
2020-07-13 10:04 ` Stefano Brivio
2020-07-13 10:51 ` Numan Siddique
2020-07-14 20:38 ` Aaron Conole
2020-07-15 11:58 ` Stefano Brivio
2020-07-13 13:25 ` David Ahern
2020-07-13 14:02 ` Florian Westphal
2020-07-13 14:41 ` David Ahern
2020-07-13 14:59 ` Florian Westphal
2020-07-13 15:57 ` Stefano Brivio
2020-07-13 16:22 ` Florian Westphal
2020-07-14 12:33 ` Stefano Brivio
2020-07-14 12:33 ` Stefano Brivio
2020-07-15 12:42 ` Florian Westphal
2020-07-15 13:35 ` Stefano Brivio
2020-07-15 14:33 ` Florian Westphal
2020-07-17 12:27 ` Stefano Brivio
2020-07-17 15:04 ` David Ahern
2020-07-17 18:43 ` Florian Westphal
2020-07-18 6:56 ` Stefano Brivio
2020-07-18 17:02 ` David Ahern
2020-07-18 17:58 ` Stefano Brivio
2020-07-18 18:04 ` Stefano Brivio
2020-07-19 18:43 ` David Ahern
2020-07-19 21:49 ` Stefano Brivio
2020-07-20 3:19 ` David Ahern
2020-07-26 17:01 ` Stefano Brivio
2020-07-12 20:07 ` [PATCH net-next 2/3] vxlan: allow to disable path mtu learning on encap socket Florian Westphal
2020-07-16 19:33 ` Jakub Kicinski
2020-07-17 10:13 ` Florian Westphal
2020-07-12 20:07 ` [PATCH net-next 3/3] geneve: allow disabling of pmtu detection on encap sk Florian Westphal
2020-07-12 22:39 ` Stefano Brivio [this message]
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