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

Wed Apr 15 22:22:28 UTC 2015
Nathan March <nathan at gt.net>

So I might have been misinterpreting things here and might be way off base. I think you can ignore this thread and I'll follow up if I get anything concrete down the road =) The retranmissions I'm seeing and reproducing are probably within normal allowances and can't reproduce the issue that originally lead me down this path.

- Nathan

> -----Original Message-----
> From: centos-virt-bounces at centos.org [mailto:centos-virt-
> bounces at centos.org] On Behalf Of Nathan March
> Sent: Wednesday, April 15, 2015 1:13 PM
> To: 'Discussion about the virtualization on CentOS'
> Subject: Re: [CentOS-virt] Seeing dropped packets / tcp retrans on latest
> 4.4.1-10el6
> 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:
> http://dpaste.com/1Q6NY3Y
> 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
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