[ovs-discuss] packets getting dropped at egress

[gowrishankar]

ifconfig br0 mtu 1600 works expectedly. Even ip link set command too.

You might need to check on why ifconfig fails to update br0. dmesg ?

Thanks,
Gowrishankar

On Friday 24 July 2015 09:26 PM, Dave Waters wrote:
> Hi,
>
> I am unable to increase the MTU of the bridge port (the internal port) 
> to be anything more than 1500. While i am able to reduce it, i am not 
> able to increase it.
>
> The reason i want to increase the MTU of the internal port is because 
> i am encapsulating all packets that i recieve on eth1 inside VXLAN 
> which increase the packet size. If i recieve a 1500 byte packet on 
> eth1, then i am dropping the packets since the size goes beyond the 
> MTU of the bridge after i put in VXLAN encapsulation.
>
> root at ubuntu:/home/dw# ovs-vsctl show
> b69c9516-a7dd-445c-a82d-8fb704e587a3
>     Bridge "br0"
>         Port "gre0"
>             Interface "vxlanIp"
>                 type: vxlan
>                 options: {key="500", remote_ip="192.168.0.1"}
>         Port "eth1"
>             Interface "eth1"
>         Port "br0"
>             Interface "br0"
>                 type: internal
>         Port "eth0"
>             Interface "eth0"
>     ovs_version: "2.0.2"
> root at ubuntu:/home/dw#
> root at ubuntu:/home/dw# ifconfig br0 mtu 1600
>
> root at ubuntu:/home/dw# ifconfig br0
> br0     Link encap:Ethernet  HWaddr 00:90:0b:35:e4:36
>           inet addr:192.16.10.147  Bcast:192.168.10.255 
>  Mask:255.255.255.0
>           inet6 addr: fe80::dc88:f5ff:feef:ef9b/64 Scope:Link
>           UP BROADCAST RUNNING  MTU:1500  Metric:1
> [clipped]
>
> root at ubuntu:/home/dw#
>
> Dave
>
> On Thu, Jul 23, 2015 at 7:49 PM, gowrishankar 
> <gowrishankar.m at linux.vnet.ibm.com 
> <mailto: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
>
>


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://openvswitch.org/pipermail/ovs-discuss/attachments/20150727/7d3689d1/attachment-0002.html>