Re: Router MAC-Addresses @ IXs

[Gert Doering <]

Hi,

On Thu, Oct 12, 2000 at 07:51:58PM +0100, Mike Hughes wrote:
> 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?

That's my theory as well.  The Chassis has a handful of MAC addresses
that are then handed out to the PAs following some algorithm, like
"8 MACs per Slot" (which would be needed for OIR on PA-8E's, for
example).

> 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?

Definitely so at the INXS and DECIX (7200s, some 71xx's, a few 75xx's and 
GSRs).

> 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.

Yep.

Gert Doering
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