Now that we've seen all the protocol details of the
multicast traceroute packets, we can put it to use to find a real network issue.
Again, a quick reminder, this is our demo network.
The R1 to R2 link is intentionally down,
but I've introduced another sneaky issue that
multicast traceroute can help us find.
This will be a very short demo.
We know we have a fault in the network.
I have already explained how mtrace works, so let's jump right in.
I'm intentionally going to leave debugging off,
so that we can find the error using Wireshark rather than Cisco iOS,
given the protocol focus of this course.
At a glance,
this output looks different than the healthy mtrace from the previous demo.
First, there is no 10.2 .5 .5 at the very end.
Second,
the traceroute appears to terminate on R3 with a no route forwarding code.
I'll do a quick ping check to see if there is a
routing problem based on this code.
Exclamation marks indicate success, so there isn't an obvious routing problem.
So what does no route actually mean? The packet captures contain the answer, so let's go find it.