VM systems and IPv6?

Gert Doering gert at space.net
Thu Mar 18 12:43:57 CET 2010


On Thu, Mar 18, 2010 at 12:28:40PM +0100, Marco d'Itri wrote:
> On Mar 18, Gert Doering <gert at space.net> wrote:
> > There's a caveat: if you enable TCP offloading in Linux VMs, the IPv6
> > TCP performance will be abysmal.
> Can you tell us more? Which virtualization solution are you talking
> about, and which kind of network setup? 

>From the part that you didn't quote: VMware ESX.

I'm not sure ESX can do anything but "virtual switches" - so that's
what we using: external links to the host are tagged, and the ESX switch
distributes the "right" VLAN to each VM.

> Is this a documented bug?

It is at least a known bug - googling finds lots of hits for "slow 
performance with IPv6 in VMware".  The recommended solution is usually 
"do not install VMware-tools" - and that works, but that's just side

Installing VMware-tools will install a RC startup script that will always 
turn on TCP offloading, and *that* is the root-cause, not the vmware-tools 
itself.  So "with VMware-tools, but without TCP offloading, things work"

We have not reported it to VMware, as their official stance on IPv6 was
"we do not support it yet" and we found a workaround.  (Also it was not
clear whether this is a VMware bug, or a Linux kernel bug in the driver
for the virtual e1000).

The virtual NIC we use on the system where I had the problem is:

$ lspci -v
00:11.0 Ethernet controller: Intel Corporation 82545EM Gigabit Ethernet Controller (Copper) (rev 01)
        Subsystem: VMware Inc Abstract PRO/1000 MT Single Port Adapter
        Flags: bus master, 66MHz, medium devsel, latency 0, IRQ 177
        Memory at f4820000 (64-bit, non-prefetchable) [size=128K]
        Memory at f4800000 (64-bit, non-prefetchable) [size=64K]
        I/O ports at 1400 [size=64]
        [virtual] Expansion ROM at 88000000 [disabled] [size=64K]
        Capabilities: [dc] Power Management version 2
        Capabilities: [e4] PCI-X non-bridge device

As I said - we found a workaround, and had other things to break & fix...

Gert Doering
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