[c-nsp] Mac Address on ATM Subinterfaces | c1712 routing issue

[Gert Doering]

Hi,

On Thu, Feb 03, 2005 at 10:11:23AM +0100, Marco Eulenfeld wrote:
> Looks like the 1712 doesn't really route first (routing via Vlan 1 or
> Vlan 2) and than looks in the ARP table of the "next-hop-vlan" for the
> L2 adress of the next hop.
> Everything works fine when there are 2 different MACs as next hops.

For a test, you might want to try to switch off CEF.  

As the CEF data structure is very tightly coupled to ARP, it sometimes 
does "interesting" things (like "forward out a packet over the wrong
ethernet if a gratituous ARP for a non-local IP address was seen there" -
as far as I know, this has been fixed long ago, though) if ARP is weird.

OTOH, the effect *you* are observing isn't so easily explained, as
CEF normally copes well with this - "same MAC address on different VLANs"
is not uncommon if you have a machine that is trunking.

Cisco>sh ip arp 0011.095c.8d75
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  193.149.xx.X            0   0011.095c.8d75  ARPA   Vlan5
Internet  195.30.2xx.X            0   0011.095c.8d75  ARPA   Vlan4
Internet  195.30.yy.X             0   0011.095c.8d75  ARPA   Vlan1

(and I can ping all of those just fine - Cat5RSM, 12.2(x), CEF on)

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de