> On Fri, Jun 26, 2009 at 8:11 AM, Ms Geekgirl<msgeekg...@gmail.com> wrote: >> On Thu, Jun 25, 2009 at 4:28 PM, Ray Burkholder<r...@oneunified.net> wrote: >>> I was wondering the reasoning for routers/switches to respond for the >>> network portion of an ip-address range. >>> >>> For example, a router interface A with 10.0.0.1/30 and interface B with >>> 10.0.0.5/30. >>> >>> Generate a ping from a device several hops away on the A side to the B side >>> network address of 10.0.0.4. The router will respond with an echo reply >>> with an address of 10.0.0.1. >>> >>> Is this expected behaviour? And the reason? >>> >>> Ray >> >> Yes. >> >> By default. you will almost always get a response from the closest interface >> to the source of the ping (*unless instructed otherwise in each hop's >> configuration.) >> >> In your example, this is what that looks like. Somewhat simplistic and others >> may have a better response, but here goes... >> >> The echo-request is sent from c1 to the IP 10.0.0.5 assigned to intB >> on dest-rtr. >> dest-rtr will receive the echo-request on intA, forward to intB. >> >> dest-rtr will lookup the best return route to your network. The return route >> chosen is towards hop2, via intA and the packet is sent out through intA. >> >> >> | > > > > > path of echo request > | >> ^ v >> [c1-B]----[A-hop1-B]----[A-hop2-B]----[(intA) dest-rtr (intB)]----[A-c2] >> ^ v >> | < < < path of reply < < | >> >> >> If you were to ping c2, the response would come from c2's IP (since this >> node only has one IP and is the closest to you :) >> >> In anticipation of a possible traceroute question, the same applies. >> >> If you were to trace to c2, the responses* would all come from the closest >> interface towards c1. In the above, all the responses would come from the >> _A_ interfaces of each hop. >> >> If c2 were to ping/trace to c1, the responses would come from the _B_ >> interfaces of each hop. >> >> I hope that I haven't confused anything and that this was helpful for you. >>
On Fri, Jun 26, 2009 at 10:04 AM, Geoffrey Pendery<ge...@pendery.net> wrote: > No, I think he's asking why the router with address 10.0.0.5 responds > to pings that have a destination IP of 10.0.0.4. The echo request is > targeted at a network address, not at the router. > > I've also observed this behavior (more than ICMP though - I have a > router responding to SNMP and being discovered by our configuration > management team, on the network address of one of its interfaces) and > would like to know more about why... > > -Geoff > My apologies. But it still *seems* that I partially answered the question that was asked. >>>> Generate a ping from a device several hops away on the A side to the B side >>>> network address of 10.0.0.4. The router will respond with an echo reply >>>> with an address of 10.0.0.1. My noobness is now showing...what did you use to view the replies(just the router's display response or a sniffer?) The reason I ask is, wouldn't all devices in network B respond to the broadcast request and it appears to be from the router's intA (unless they were configured not to respond??) Thanks. - - - mgg Like a seedling in the Spring, green and vulnerable. _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/