Ping and Traceroute

jwills

In Odems ICND 2 book, on pages 285 - 286, there is an example where a router does a traceroute and cannot get a reply back from anything, not even the next hop router. Then he pings the next hop router and gets 100% successful. How can he ping the router successfully, but not get a successful response from the traceroute. He mentions the traceroute uses the routing table (with this example the routing table is incorrect, therefore he cannot get a response from the traceroute) but wouldn't the ping command use the routing table also and get the same response?

Thanks

captobvious

If you look at the touting table for R3, page 287, the route for 10.1.13.0/24 is a connected route. This would make the ping from R1 to R3 successful as this is the route the ping to 10.1.13.3 would take.

R3 has two routes to 10.1.1.0, /26 and /24. Therefore the traceroute to 172.16.2.7 sourced from FA0/0 on R1 (10.1.1.1) will use the more specific route, 10.1.1.0/26 to forward the packets intended for 10.1.1.1 out R3's link to R2 (via 10.1.23.2), instead of to R1 (via 10.1.13.1). Therefore, the traceroute fails.

Page 287 spells all this out.

jwills

OK, cool. I see that now. I did not catch that the source was 10.1.1.1 that the traceroute was coming from. Thanks for your help.