[ovs-discuss] Unexpected retransmissions

[Abhishek Chanda]

Hi Jesse,

Thanks for the reply.
I ran tcpdump on all interfaces and it shows the same thing:
retransmissions on the switch side and no retransmissions on the client
side. I observed that, the behavior is exactly the same if I remove my
controller (floodlight) and let OVS be in default mode without any custom
flows. I am wondering if this is a problem with my configuration. Here is
what I did:

1. Added four tap devices on a Ubuntu box, brought them up
2. Assigned each tap device as an interface to 4 VMs on Virtualbox
3. Created a bridge in OVS and added all tap devices as ports to the bridge
4. Turned on the VMs and assigned IP addresses (now all VMs can ping each
other)
5. Hosted a web server on one VM and accessed it from a client on another

Am I missing something here?

Thanks

On Tue, Aug 14, 2012 at 1:14 PM, Jesse Gross <jesse at nicira.com> wrote:

> On Tue, Aug 14, 2012 at 10:37 AM, Abhishek Chanda
> <abhishek.lists at gmail.com> wrote:
> > Hi all,
> >
> > I have a number of VMs connected over OVS. One of the VM hosts a web
> server
> > and another VM connects to it. I am trying to debug an issue where it
> seems
> > that the client VM sends out a http packet which is received twice at the
> > destination. I ran wireshark on the client VM and the switch, wireshark
> on
> > the client's outgoing interface shows that the http packet was
> transmitted
> > once but wireshark on the switch's corresponding incoming interface
> shows a
> > tcp retransmission for the same packet. I assumed that the switch was
> > dropping the packet. When can this happen?
>
> If the packet was dropped somewhere in the network then you would see
> the retransmission on the client VM, since it is the one running the
> TCP stack.  I would run tcpdump at each interface in the path and see
> what exactly is happening to the packets in between each segment.
>
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