[c-nsp] Bridge group woes and IRB

[Gert Doering]

Hi,

On Wed, Apr 20, 2005 at 10:49:51AM -0400, David Coulson wrote:
> With the second configuration, when I traceroute from 207.166.219.6
> across the router to something, it completly skips the router at layer 3
> - I don't see a TTL decrease in IP packets. This to me indicates that
> the router is bridging packets between the two interfaces, rather than
> routing as I would expect

Could just be a TTL/CEF bug.  Not unheard of.

Bridging (or just "physically connecting those two VLANs") will not
enable the machines in them to talk to each other -  all will still
ARP for their default gateways, and send the packets to that machine.

You can easily verify whether it's routing or bridging: run a network
sniffer program on source and destination host, and look at the ethernet
header.  If it's routed, you'll see different ethernet headers on src and
dst host (src host: src=host, dst=cisco, dst host: src=cisco, dst=host) -
and with bridged, you'll see the same header.

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