[clug] Network bridges behind wireless ethernet bridges

Angus Gratton gus at projectgus.com
Sat Dec 17 00:05:24 MST 2011

Hi Ed,

On Sat, 2011-12-17 at 17:31 +1100, Edward C. Lang wrote:
> I noticed that once I'd configured the bridged network connection on
> KVM host, my connection to it from my PC kept dropping out. 

When you say the connection kept dropping out, do you mean that you
could get packets both ways across the link for a while, but they'd
intermittently stop? Did they ever start again?

Are you able to run packet captures to see if packets make it one way or
both ways across? At least if ARPs get across?

Does it only fail if you have more than one guest running on the KVM

On Sat, 2011-12-17 at 17:31 +1100, Edward C. Lang wrote:
> I'm beginning to suspect it's due to the double duplication of MAC
> addreses: from my PC's perspective, everything behind the wifi bridge
> shared the same MAC address; and then the host's network bridge again
> reused the physical MAC address. Is that correct? Or am I wrong on that
> assumption? I know little about this sort of networking and perhaps
> stacking network bridges is well known to be silly...

I've found the ARP NATting that wifi bridges do to be pretty haphazard,
for the reasons you describe. I had that setup in my house for a while
and although I got it fairly stable, I was never 100% happy with it.

However if the problem is actually "intermittent" or unpredictable that
makes me think of wifi signal problems, or WPA rekeying problems, or
something like that.

If it was me I'd try:

* Confirming the wifi bridge link is stable without any KVM bridge on
it. Might just be an unstable wifi combination or specific WPA/WPA2

*  Running WDS if possible, so both routers can "have" multiple MACs (I
find different brands of routers can be fussy about playing together on
this front, but you may be lucky.)

* If all else fails, I've actually had good luck with brandname
"ethernet over powerline" adapters. Better throughput than 802.11g wifi,
and better latency, although not at all comparable to real ethernet.


- Angus

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