Re: Router MAC-Addresses @ IXs

[Mike Hughes <]

On Thu, 12 Oct 2000, Christian Panigl, ACOnet/VIX/UniVie wrote:

>     Now it turned out, probably because "Vienna is different", that more
>     than 90% of all (Cisco) router FastEthernet interfaces connected to the
>     Vienna Internet eXchange have MAC addresses ending with Hex 0 !!!  And
>     nope, it's not Halloween today (for those who understand German ;-)

I wonder if it's because of the position that the FE interfaces are in
people's Cisco interfaces, coupled with the way the MAC addresses are
handed to the port adapter by the chassis in 7xxx boxes, that you tend to
end up with Hex 0?

I've noticed that on all LINX's own 7200s, fa0/0 ends in 0, and fa1/0
ends in 8, for example. Looking at the LINX table (which Jesper has sent,
so I won't waste bandwidth), I see a lot of 0's and 8's. Could it be that
there are a lot of people with fa0/0 of 7200's connected to the VIX?

We appear to have found a flaw in the Cisco load-balancing hash, which is
expecting mostly end-stations (servers/workstations with NICs) with a wide
spread of low bits. Of course, we then hit this with they way C7xxx boxes
give out MAC addresses and it all goes wonky.

>     This of course does break port-group load-balancing on any such switch
>     with only routers connected ... :-(
>     
>     Any ideas, similar experiences, workarounds (other than to assign MAC
>     addresses to exchange point routers) ?

Extreme implement round-robin per packet load sharing, which may help, as
well as source port-based and destination MAC-based load-sharing. Foundry
implement source MAC or destination MAC load sharing.

LINX don't seem to suffer too badly regarding imbalances on our trunk
groups. Not sure if it's just that Foundry and Extreme's algorithms are
more clueful than Cisco's or the distribution of addresses is better.

Mike
-- 
Mike Hughes	Network Architect	London Internet Exchange
mike@localhost	http://www.linx.net/	
     "Only one thing in life is certain: init is Process #1"