[ovs-discuss] packets getting dropped at egress

Abhishek Verma abhishekv.verma at gmail.com
Sat Jul 25 19:00:10 UTC 2015


I think the only way to fix this issue is by configuring other devices in
your network with an MTU < 1500. This way, when your OVS gets the packet,
it can slap on additional headers and still get the packet across since the
overall length would be <= 1500.



On Sat, Jul 25, 2015 at 11:00 AM, Dave Waters <davewaters1970 at gmail.com>
wrote:

> In my case all my NIC cards can support jumbo frames. So i can really send
> a 1600 byte packet. However, i am being restricted by the OVS's internal
> port's MTU which is fixed to 1500. As a result i am unable to send out
> larger packets (because of the VXLAN header addition). Can somebody please
> help me here?
>
> Dave
>
> On Fri, Jul 24, 2015 at 10:39 PM, Dave Waters <davewaters1970 at gmail.com>
> wrote:
>
>> That wouldnt work since anybody connected to portA and sending a 1500
>> byte packet, would be unable to do so.
>>
>> Is there a known limitation wherein i can increase the MTU of an internal
>> bridge port?
>>
>> Dave
>>
>> On Fri, Jul 24, 2015 at 10:32 PM, Joe Stringer <joestringer at nicira.com>
>> wrote:
>>
>>> Have you tried decreasing the MTU of portA such that packets are
>>> encapsulated they're <=1500B?
>>>
>>> On 23 July 2015 at 08:19, Dave Waters <davewaters1970 at gmail.com> wrote:
>>> > Its not. But how do i ensure that my packet does not get dropped
>>> somewhere
>>> > downstream, since i have now increased it beyond the original value?
>>> >
>>> > On Thu, Jul 23, 2015 at 7:49 PM, gowrishankar
>>> > <gowrishankar.m at linux.vnet.ibm.com> wrote:
>>> >>
>>> >> On Thursday 23 July 2015 04:16 AM, Dave Waters wrote:
>>> >>>
>>> >>> Hi,
>>> >>>
>>> >>> I have two ports in my OVS bridge. I receive packets from one port
>>> >>> (portA) and i send them out of the other (portB). When i send out the
>>> >>> packets, they are VXLAN tunneled to the other end.
>>> >>>
>>> >>> Now, the default MTU of all ports (including the bridge port) is
>>> 1500 in
>>> >>> my setup.
>>> >>>
>>> >>> The issue is that when i get a 1500 byte packet on portA, i try to
>>> push
>>> >>> it out on portB after slapping on the VXLAN headers. This results in
>>> a
>>> >>> packet size thats greater than what portB can handle, and hence the
>>> packets
>>> >>> are dropped.
>>> >>>
>>> >>
>>> >> Is increasing MTU of portB to 1550 (to accommodate additional 50 bytes
>>> >> when no vlan taged) a constraint in your setup ?
>>> >>
>>> >>
>>> >>> I know that OVS does not handle IP fragmentation/reassembly, so how
>>> do we
>>> >>> deal with this situation? I dont think we can rely on path MTU
>>> discovery
>>> >>> since not all applications do PMTU before spewing out packets. Any
>>> ideas,
>>> >>> anybody?
>>> >>>
>>> >>> Warm regards,
>>> >>> Dave
>>> >>>
>>> >>
>>> >> --
>>> >> Regards,
>>> >> Gowrishankar M
>>> >>
>>> >
>>> >
>>> > _______________________________________________
>>> > discuss mailing list
>>> > discuss at openvswitch.org
>>> > http://openvswitch.org/mailman/listinfo/discuss
>>> >
>>>
>>
>>
>
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