Priscilla Oppenheimer wrote: > > s vermill wrote: > > > > Anyone smart on interworkings of Cisco routers care to clarify > > something for me? I was in a discussion with someone in > > another forum. It was being discussed how pings from a local > > ethernet interface to a local serial interface on the same > > router actually cross the WAN to which that serial interface is > > attached and are returned by the distand-end router. > I'm not totally sure what you mean by "from a local ethernet interface". If you mean that the router forwarded a packet that arrived on its Ethernet interface, and the destination was its serial IP, then the packet will definitely *not* leave the router.
OTOH, if the router itself is the source of the packet, and it pings its own serial IP, and the outbound interface and layer 2 encap are resolved and unambiguous, then the router will launch the packet out that p2p interface or PVC. I have done exactly what Priscilla describes, and not only seen the output from "debug ip icmp" on the neighbor router, but also observed it generating ICMP redirects, since the packet was forwarded out the interface it arrived on! This Cisco aberation is extremely useful for troubleshooting p2p WAN links. When the path has been looped (line protocol up (looped)), the only IP that is pingable is the directly connected one. That the router actually sends the packet makes it possible to test the link with ping. Now I wasn't performing an extended ping and sourcing the ping from a different interface. Maybe that's the difference? I last did this with IOS 12.0(7)T. Priscilla, I'm not saying what you observed is wrong! I don't have access at the moment to replicate it, but I'm positive of what I saw -- I had my students do it in class numerous times. - Marty Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=53161&t=53148 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
