[ovs-discuss] Path MTU Discovery

[Thomas Glanzmann]

Hello David,
enable jumbo frames in your network. The GRE tunnel and VXLAN add
overhead. If you're switches chop the packet other 1500 Bytes you see
exactly this effect:

        - Ping works
        - TCP works
        - But as soon as you do burst transfers the TCP connection
          stalls.

In order to avoide the problem you either have to lower the MTU in the
VMs which you did or you enable bigger packets in your transport
network. This is called jumbo frames. On HP procurve switches they're
enabled by saying

        vlan x
        jumbo

You also have to increase the MTU of the physical uplinks of the server
and if you're doing VXLAN or GRE over Layer 3 the ones of your routers.

Cheers,
        Thomas