s vermill wrote: > > > > > This doesn't sound believable to me. It sounds like the > > discussion mangled some slightly related topics and applied > > them to this situation. ;-) Or that someone misinterpreted the > > output from "debug ip icmp." Or perhaps someone jumped to this > > conclusion due to the fact that you have to map your serial > > interface IP address to a DLCI to ping it in a Frame Relay > > environment. > > Priscilla, > > Thanks. Here is one link I crossed on CCO recently: > > http://www.cisco.com/warp/public/116/fr_faq.html#1
Don't believe everything you read. ;-) This statement from the Cisco document is not believable: "Pings to your own interface address are successful on point-to-point subinterfaces or high-level data link control (HDLC) links because the router on the other side of the link returns the ICMP echo and echo reply packets. The same principle applies with multipoint (sub)interfaces. To successfully ping your own interface address, another router must send back the ICMP echoes and the echo replies." I think they are trying to address the issue of not being able to ping yourself on Frame Relay. That is fixable by including a map statement. This shouldn't imply that the packets actually cross the serial link though, even though that's what they are saying. And to claim that the echos (not just the echo replies) get sent back is really not believable. On the other hand, sometimes things that aren't believable turn out to be true in the Cisco world. But this one really smacks of a being written by someone who is slightly clueless. Hey, ask Chuck about that weird EIGRP paper that comes up every so often. It's even more unbelievable than this one. ;-) Priscilla > > I have found other similar links and discussions over the > years. In fact, I was thinking that it might have been you > that once explained how it all worked. In any case, I have > tried some of the same debug that you have in the past. I > assumed that what was going on was somehow hidden from debug. > > > > To forward a frame a router looks into its routing information > > base, (whether that be the routing table, fast cache, or > > whatever), and determines how to forward the frame. In this > > case, it would see that the destination network is directly > > connected and from there it would presmumably check its > running > > config and see that the destination node is directly connected > > also. So there's no need to send the frame out an interface. > > > > Anyway, I tested it. I tried various serial encaps, including > > HDLC, Frame Relay, and PPP. I was consoled into two routers at > > once, Router A and Router B, to make it easy to see the output > > from "debug ip icmp" on both routers. The router serial > > interfaces are connected back-to-back. When I pinged from > > Router A's e0 to Router A's s0, Router B did not see the > > packets. I don't believe they crossed the serial link. > > > > To be absolutely sure I would want to use a serial protocol > > analyzer, but alas, those are too expensive for the > > self-employed. But I'm 99% convinced by the testing that I > did. > > > > Priscilla > > This is exactly why I have been looking into building my own > WAN protocol analyzer. There are a few PCMCIA cards on the > market that do synchronous, bit-oriented protocols. Ethereal > apparently supports Cisco's perversion of HDLC. But those > PCMCIA cards aren't exactly cheap either. > > In any case, this discussion stemmed from someone's problem > whereby he was observing dropped packets on an extended ping > from an ethernet interface to a serial interface on the same > router. The router CPU and memory was apparently virtually > untapped. Yet, he observed packet loss. He specifically asked > if pings were required to cross the WAN. I remembered having > read about it in the past. Is it possible that I have just > misinterpreted it every single time I've read it? You bet! > Any thoughts on what CCO is really saying? > > My brain hurts.... > > Thanks again, > > Scott > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=53158&t=53148 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
