[CentOS-virt] Seeing dropped packets / tcp retrans on latest 4.4.1-10el6

Wed Apr 15 20:12:31 UTC 2015
Nathan March <nathan at gt.net>

Hi All,

Some more data on this, I've reproduced this on another host that's a completely stock centos/xen deployment with a centos 6.6 domU.

Since I’m seeing the retransmissions on the VIF, I don't think it's related to the network stack but just in case.. Each host is connected via LACP with vlan tagging to a pair of stacked cisco 3750's. Host networking config is here: 


The vm is on br99 here.

This is easily reproducable by just generating a 250mb random file and doing an scp, while watching with tshark: 

tshark -R "tcp.analysis.retransmission"

There's no visible impact to the connection the vast majority of the time, which is why I think this has gone unnoticed.

Just to confirm this wasn't related to hardware / nics, I've reproduced this on:

 - Dell PowerEdge M620 with broadcom nics
 - Dell C6220 with intel nics
 - Supermicro X8DTT with intel nics

Any ideas? =)

- Nathan