Is it possible two routers can see each other through show cdp neighbor when there is a firewall between the two?

[wfqk]

Is it possible two routers can see each other through show cdp neighbor when there is a firewall between the two? The connection is port-channel with ip address between the two routers. Thank you

[Yeshwanth Simhadri]

- To my knowledge CDP (Cisco Discovery Protocol) is a Cisco proprietary protocol that runs between direct connected network entities

- I have checked the ASA (firewall) in my environment and CDP dose not play a role

- Hope im correct :(

[pwwiddicombe]

CDP is L2 only and non-routable, so if the firewall's interfaces have different ip addresses, it definitely wouldn't work.  However, something like a viruswall or "transparent" firewall that passes everything through might allow it.

...  but if a firewall DID allow CDP through, it doesn't sound like it's doing it's job; unless it's purpose was to simply block specific traffic.