[c-nsp] CDP over ATM

[Gert Doering]

Hi,

On Tue, Feb 01, 2005 at 03:47:56PM -0600, rbf+cisco-nsp at panix.com wrote:
> > ... interesting enough, the router on the *other* end doesn't see the
> > CDP packets (ATM-VC -> bridging DSL modem -> Ethernet -> Cisco).   Can't
> > say whether the CDP packets aren't sent, or whether the DSL modem is
> > eating them.
> 
> CDP over ATM is likely encapsulated directly in ATM; for what you
> describe above to work, you'd need the CDP packets to be encapsulated
> in bridged ethernet packets.  (That is, you want CDP over Bridged
> Ethernet over ATM, not CDP over ATM.  Or, put another way, you want
> "atm route-bridged cdp", which doesn't actually exist.)

Thanks.  This is very likely the case - IP is run "route-bridged ip"
on the interface in question, not "plain IP over aal5snap".

> It works in the reverse direction because the router is (presumably)
> being liberal in what it receives, so CDP packets are accepted whether
> they are natively encapsulated or encapsulated in Ethernet.

Which would explain the asymmetry.

Well.  It's useful anyway, even if only to see whether it's really the 
customer's router on the far end, and not "something mis-routed by
the Telco".

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