netdev - Lab: v.1.8 + Linux 2.6.37.6+up #1 + ESXi 5.0 - VM

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Date:	Fri, 28 Sep 2012 04:56:35 +0200
From:	Mike Harris <mharris@...is.com>
To:	netdev@...r.kernel.org
Subject: Lab: v.1.8 + Linux 2.6.37.6+up #1 + ESXi 5.0 - VM - Slow Network Performance/Failures

Hi,

I hope everyone is well!

Some network throughput/performance oddness with a linux based virtual firewall…

Lab scenario;

[Windows VM #1] --- VLAN X-----(*)Linux Firewall VM ----- VLAN Y
---[Windows VM #2]

A tcpdump is kicked off with the following options on the firewall
this a 100MB file is copied between VM #1 to VM #2 (SMB).

tcpdump -i eth0.x -n -s0 -w file-transfer-1.pcap -c100

Notes:

+ Physical blade run ESXi 5.0.
+ Windows VMs run on the same vSwitch and physical blade.
+ VLAN X and Y support up to 1500 bytes MTU.
+ Virtual firewall is configured with the 4095 (any) VLAN (receives
and transmits tagged frames).
+ Virtual firewall is runs Linux 2.6.37.6+up #1
+ Virtual and physical backbones do support up to 9k frames.

Observations;

1. The file copy fails…
2. The pcap reveals a 12,443 byte uber jumbo frame is present shortly
after the file transfer starts.

Repeated the same scenario using a test vyatta 6.4 VM and the file
copy completes normally… no jumbo frames or any other oddness.
Virtual and physical networking can not originate such a frame
normally.

Given this, I suspect there's a general framing failure of the network
driver on the virtual linux firewall, which lead me to the dmesg
command and this mailing list :)

Has anyone else seen this behavior before on a linux VM before?

Thoughts?

Helpful suggestions :)

Mike
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