Re: [lvs-users] LVS/DR Packet Loss Problem

To: " users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [lvs-users] LVS/DR Packet Loss Problem
From: chchen@xxxxxxx
Date: Tue, 25 Jan 2011 10:09:28 -0800
Quoting btinsley <btinsley@xxxxxxxxx>:
> Hi list,
> Has anyone experienced packet loss issues on real servers in an LVS/DR
> configuration? I don't believe this is an LVS issue per se, but I am
> curious if anyone else has experienced the same problem.
> What I am seeing is packets are being forwarded from the director to the
> real server, but once they arrive at the real server there is packets
> loss such that it totally breaks communication with the client (at the
> TCP level). It seems to be fairly specific to loosing delayed ACKs. I
> see this reflected in the /proc/net/netstat statistics on the client
> (DelayedACKLost and TCPDSACKOldSent) and in a side-by-side comparison of
> tcpdump captures on the real server's receiving interface (bond1) and
> transmitting interface (bond0). The dummy0 interface is configured with
> the VIP on the real server and I have tried using the loopback interface
> with the same result. We have been using this same configuration for
> several years, so I am certain that there are no incorrect sysctl values
> (e.g., arp_announce, arp_ignore, etc) and there is no interference from
> netfilter.
> This was first noticed on the SLES11 SP1 kernel, which is based on
> 2.6.32. In the process of gathering information to open a case with the
> vendor, I found that the same problem occurrs on the
> version. Further testing revealed that the issue was
> reproducible on all versions (2.6.[32-36]) up to stable
> 2.6.37, when it no longer happens. It also works on the SLES11 SP0
> kernel, which is 2.6.27 based.  I have looked through the git changelogs
> for the kernel across all versions and there do no seem to be any
> changes that would indicate why this is happening, but I don't claim to
> be an expert here. I have also searched the LVS mailing list archives in
> some depth and found nothing.
> If anyone has had a similar experience, I would appreciate any
> information you may be able to share.

Yes--I've seen it with the lvs bundled with RHEL4 and 5 DR, and it  
seems to particularly anger connections from Windows 7 SSL/TLS  
clients. I'll give .37 a shot and let you know what I see!


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