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From: David Miller <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
To: david-1SEAoVOfG6VEzL6FDj/jAg@public.gmane.org
Cc: dev-yBygre7rU0TnMu66kgdUjQ@public.gmane.org,
	netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH net 0/2] vxlan: Set a large MTU on ovs-created vxlan devices
Date: Wed, 06 Jan 2016 15:59:50 -0500 (EST)	[thread overview]
Message-ID: <20160106.155950.1007160228570301281.davem@davemloft.net> (raw)
In-Reply-To: <1452087186-12926-1-git-send-email-david-1SEAoVOfG6VEzL6FDj/jAg@public.gmane.org>

From: David Wragg <david@weave.works>
Date: Wed,  6 Jan 2016 13:33:04 +0000

> Prior to 4.3, openvswitch vxlan vports could transmit vxlan packets of
> any size, constrained only by the ability to transmit the resulting
> UDP packets.  4.3 introduced vxlan netdevs corresponding to vxlan
> vports.  These netdevs have an MTU, which limits the size of a packet
> that can be successfully vxlan-encapsulated.  The default value for
> this MTU is 1500, which is awkwardly small, and leads to a conspicuous
> change in behaviour for userspace.
> 
> These two patches set the MTU on openvswitch-crated vxlan devices to
> be 65465 (the maximum IP packet size minus the vxlan-on-IPv6
> overhead), effectively restoring the behaviour prior to 4.3.  In order
> to accomplish this, the first patch removes the MTU constraint of 1500
> for vxlan netdevs without an underlying device.

Is this really the right thing to do?  Won't we get a lot of fragmentation
by using such a large MTU, especially since you're making it the default
for OVS setups?

Things like path MTU discovery hinge strongly upon accurate MTU settings.
Otherwise they won't function properly.
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  parent reply	other threads:[~2016-01-06 20:59 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-06 13:33 [PATCH net 0/2] vxlan: Set a large MTU on ovs-created vxlan devices David Wragg
     [not found] ` <1452087186-12926-1-git-send-email-david-1SEAoVOfG6VEzL6FDj/jAg@public.gmane.org>
2016-01-06 13:33   ` [PATCH net 1/2] vxlan: Relax the MTU constraint on " David Wragg
     [not found]     ` <1452087186-12926-2-git-send-email-david-1SEAoVOfG6VEzL6FDj/jAg@public.gmane.org>
2016-01-07 11:24       ` Thomas Graf
2016-01-07 11:31         ` David Wragg
2016-01-07 11:50           ` Thomas Graf
2016-01-09 18:39       ` roopa
2016-01-10 10:28         ` [ovs-dev] " Thomas Graf
2016-01-27 16:39           ` roopa
2016-01-06 20:59   ` David Miller [this message]
     [not found]     ` <20160106.155950.1007160228570301281.davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
2016-01-06 22:53       ` [PATCH net 0/2] vxlan: Set a large MTU on ovs-created " Jesse Gross
2016-01-06 23:25       ` David Wragg
2016-01-06 23:57         ` [ovs-dev] " Jesse Gross
2016-01-07  0:14           ` Hannes Frederic Sowa
2016-01-07  0:46             ` Jesse Gross
2016-01-07 11:49               ` Thomas Graf
     [not found]                 ` <20160107114935.GJ32456-4EA/1caXOu0mYvmMESoHnA@public.gmane.org>
2016-01-07 16:35                   ` Jesse Gross
2016-01-07 17:21                     ` [ovs-dev] " Thomas Graf
2016-01-07 17:50                       ` Hannes Frederic Sowa
     [not found]                         ` <568EA55A.7070305-tFNcAqjVMyqKXQKiL6tip0B+6BGkLq7r@public.gmane.org>
2016-01-07 18:40                           ` Thomas Graf
     [not found]                             ` <20160107184042.GB24672-4EA/1caXOu0mYvmMESoHnA@public.gmane.org>
2016-01-08 21:29                               ` Hannes Frederic Sowa
2016-01-10 10:49                                 ` [ovs-dev] " Thomas Graf
     [not found]           ` <CAEh+42iWSZOyikNydU2Bs8meqYfrKfUJLDGFJ8HzQ06k64LP0g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-01-07  0:29             ` David Wragg
     [not found]               ` <86wprmp6z6.fsf-1SEAoVOfG6VEzL6FDj/jAg@public.gmane.org>
2016-01-07  1:10                 ` Jesse Gross
2016-01-07 21:47         ` David Miller
2016-01-07 23:42           ` David Wragg
2016-01-08  2:48             ` David Miller
2016-01-06 13:33 ` [PATCH net 2/2] " David Wragg
     [not found]   ` <1452087186-12926-3-git-send-email-david-1SEAoVOfG6VEzL6FDj/jAg@public.gmane.org>
2016-01-07 11:36     ` Thomas Graf

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