This is one of multiple IP version six troubleshooting videos in this network.
We've been told that router one on the left cannot ping the loopback of router three, the router on
the right.
So let's verify that now because this is IP version six rather than IP version four.
Notice no IP version for routes exist in the routing table.
We need to do all our testing using IP version six.
So I'm going to ping the loopback of router three.
We get a failure.
We are not able to ping the loopback of router three.
Let's do a trace router and see how far we get.
Okay.
So what do you think about this output?
What's going on here?
Notice we told that the destination was not found inside the max hop count diameter.
So let's do that again.
Notice what's happening.
So where is the traffic going?
Now this is a good example of a rotting loop.
So if we scroll up.
Notice what's happening.
Traffic goes to rather to.
Then it goes to write a one.
Then to write it to.
Then to write a one back to write it to back to write a one and so forth and so on.
So we have a loop taking place here.
So let's have a look at the routing table show IPv6 route.
Rather, one has a default route to 2001 colon one colon colon two which is rather two.
Hence the traffic is being sent to rather two.
But on router two show IPV six route.
Can you see the problem here?
Pause the video if you need to, but see if you can find the problem.
Okay.
So we have a static default route to router three that looks okay.
There's a static route to the loopback of router one that also looks okay.
Here's a static route to the loopback of router three, but that looks wrong.
Notice where it's pointing.
It's saying to get to the loopback of router three, we need to go via rather one.
So that's definitely not right.
And it's kind of redundant because we have this default route in the routing table.
So show run pipe include route.
We need to get rid of this route.
And either fix the next hop or simply remove it and rely on the default route here.
So Ken wrote a one ping.
The loopback of router three.
Okay.
The pings are still failing.
Let's do a trace to that address.
The packet gets sent to.
Brought to, but then goes nowhere else.
So it doesn't look like it gets any further based on that output.
So Ken wrote it to ping the loopback of router three.
Yes, it can.
So rather to keeping the loop back over rather three, but rather one comping the loop back of rather
three.
So on rather three.
Let's do a debug.
And check if the traffic is actually getting to router three from router one and we can see that it
is so we can see that the pings are arriving at rather three, but it looks like the reply is not getting
back to right of one.
So rather three received an echo request from 2001.
Colon one colon.
Colon one which is rather one destination is the loopback of router three.
So the echo reply is sent, but it's not getting back again.
So let's turn off debugging.
And that's to a debug IPV six packet.
Now, in the real world, you need to be very careful doing this.
I'm going to send a single packet and let's see what happens.
Again, be very careful doing this in the real world.
You'll get a lot of output.
Even in the small network, if we don't turn off debugging, we might get a lot of output on the console.
So there's the debug I sent a single ping from router one two out of three.
We got a destination lookup for that.
The router sees that as a local network connected to the loopback.
So that looks good.
But notice here IPV six forward no router to destination 2001.
Colon one colon.
Colon one source is the loopback of rudder three destination is the gigabit zero zero interface of router
one and we told that there's no valid route so it doesn't look like router three knows how to get back
to rata one so show IPV six route is there raft in the routing table to get back to rata one and the
answer is no.
We have this static route which would allow router three to ping the loopback of router one, but it
can't ping 2001.
So what we need to do is add a static route to 2001 colon one, colon colon zero.
Slash 64.
And send that to.
Rata to.
Now let's do the ping again.
Notice the ping succeeded.
And without using the repeat command, the pings now succeed.
So we can get to the loopback of router three and we can get to the physical interface of router three.
So be careful with pings.
This applies to both IP version four and IP version six.
Just because I can send traffic to you doesn't mean that you know how to send traffic back to me.
Both sides need routes in the routing table to enable two way communication.
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I wish you all the very best.