Re: [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@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@ubuntu:/home/dw#
root@ubuntu:/home/dw# ifconfig br0 mtu 1600

root@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@ubuntu:/home/dw#

Dave

On Thu, Jul 23, 2015 at 7:49 PM, gowrishankar <gowrishanka...@linux.vnet.ibm.com <mailto:gowrishanka...@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

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