Re: [PATCH net 2/2] vxlan: Set a large MTU on ovs-created vxlan devices
From: Thomas Graf <hidden>
Date: 2016-01-07 11:36:41
On 01/06/16 at 01:33pm, David Wragg wrote:
Prior to 4.3, 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. This sets the MTU on openvswitch-created vxlan devices to be 65465 (the maximum IP packet size minus the vxlan-on-IPv6 overhead), effectively restoring the behaviour prior to 4.3. Although the vxlan_config struct already had a mtu field for this, vxlan_dev_configure mostly ignored it; that is also addressed here.
I agree with Jesse that this is fine. The tunnel net_device is a logical device anyway and the real MTU is not known at this point until the underlay route has been resolved. It is really a model we should move away from though. Unless the endpoints negotiate a proper MTU, the underlay can't possible cope with this correctly without major performance problems due to fragmentation.
quoted hunk
@@ -2810,6 +2809,12 @@ static int vxlan_dev_configure(struct net *src_net, struct net_device *dev, needed_headroom = lowerdev->hard_header_len; } + if (conf->mtu) { + err = __vxlan_change_mtu(dev, lowerdev, dst, conf->mtu);
OK, I see the reason for the indirection in the first patch. Never mind. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev