[ovs-discuss] can not create device problem

Jesse Gross jesse at nicira.com
Fri Jul 9 19:31:34 PDT 2010


On Fri, Jul 9, 2010 at 7:02 PM, Yan <yan.p.bjtu at gmail.com> wrote:

> Thanks a lot for your help, but could you please offer more information
> about:
> 1. You said that
> The GRE tunnel ports have a 1500 byte MTU.  If your packets are larger than
> this they will be dropped and it will be logged in the kernel message
> buffer.
> Is there any methods to modify it much bigger?
>

At the moment, no.  Internally GRE is capable of having its MTU set but it
is not exposed.


>
> 2.If there are more than one physical NICs on a host, does OVS GRE build
> its stack for each Linux-IP? The situation is like host1 owns a
> public IP and a private IP, the other host2 only hold a private IP, host2
> build the tunnel via the only NIC to host1's public IP, but when host1 can
> only send back packets to host2 via its private IP NIC.
> When build tunnel I give two parameter remote IP and MAC, does OVS then
> judge which NIC to use or just build stack for each IP?
>

Packets are sent based on the host routing table, so that will determine
which NIC is used.  When they are received, the source IP is used to lookup
which tunnel should be the recipient.  As a result, if host1 is sending
using the public IP and host2 is sending using the private IP packets will
not get through.
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