1
00:00:09,320 --> 00:00:15,260
This is one of multiple IP version six troubleshooting videos in this network.

2
00:00:15,320 --> 00:00:23,000
We've been told that router one on the left cannot ping the loopback of router three, the router on

3
00:00:23,000 --> 00:00:23,720
the right.

4
00:00:24,470 --> 00:00:30,920
So let's verify that now because this is IP version six rather than IP version four.

5
00:00:30,950 --> 00:00:35,330
Notice no IP version for routes exist in the routing table.

6
00:00:35,600 --> 00:00:39,230
We need to do all our testing using IP version six.

7
00:00:39,950 --> 00:00:43,460
So I'm going to ping the loopback of router three.

8
00:00:44,060 --> 00:00:45,490
We get a failure.

9
00:00:45,500 --> 00:00:50,660
We are not able to ping the loopback of router three.

10
00:00:51,500 --> 00:00:53,930
Let's do a trace router and see how far we get.

11
00:00:55,680 --> 00:00:56,040
Okay.

12
00:00:56,040 --> 00:00:58,650
So what do you think about this output?

13
00:00:59,840 --> 00:01:01,730
What's going on here?

14
00:01:02,090 --> 00:01:08,360
Notice we told that the destination was not found inside the max hop count diameter.

15
00:01:09,330 --> 00:01:10,890
So let's do that again.

16
00:01:11,250 --> 00:01:12,660
Notice what's happening.

17
00:01:13,550 --> 00:01:15,770
So where is the traffic going?

18
00:01:17,180 --> 00:01:21,210
Now this is a good example of a rotting loop.

19
00:01:21,230 --> 00:01:22,850
So if we scroll up.

20
00:01:22,970 --> 00:01:24,350
Notice what's happening.

21
00:01:24,650 --> 00:01:26,750
Traffic goes to rather to.

22
00:01:26,990 --> 00:01:28,790
Then it goes to write a one.

23
00:01:28,850 --> 00:01:30,470
Then to write it to.

24
00:01:30,650 --> 00:01:36,850
Then to write a one back to write it to back to write a one and so forth and so on.

25
00:01:36,860 --> 00:01:39,710
So we have a loop taking place here.

26
00:01:40,780 --> 00:01:44,110
So let's have a look at the routing table show IPv6 route.

27
00:01:44,620 --> 00:01:52,810
Rather, one has a default route to 2001 colon one colon colon two which is rather two.

28
00:01:53,170 --> 00:01:56,800
Hence the traffic is being sent to rather two.

29
00:01:57,370 --> 00:02:01,870
But on router two show IPV six route.

30
00:02:04,110 --> 00:02:06,060
Can you see the problem here?

31
00:02:06,300 --> 00:02:10,350
Pause the video if you need to, but see if you can find the problem.

32
00:02:11,650 --> 00:02:11,950
Okay.

33
00:02:11,950 --> 00:02:17,500
So we have a static default route to router three that looks okay.

34
00:02:17,920 --> 00:02:22,810
There's a static route to the loopback of router one that also looks okay.

35
00:02:22,900 --> 00:02:27,970
Here's a static route to the loopback of router three, but that looks wrong.

36
00:02:28,510 --> 00:02:30,040
Notice where it's pointing.

37
00:02:30,460 --> 00:02:36,010
It's saying to get to the loopback of router three, we need to go via rather one.

38
00:02:36,190 --> 00:02:38,380
So that's definitely not right.

39
00:02:38,380 --> 00:02:43,930
And it's kind of redundant because we have this default route in the routing table.

40
00:02:43,960 --> 00:02:47,200
So show run pipe include route.

41
00:02:47,620 --> 00:02:50,500
We need to get rid of this route.

42
00:02:51,230 --> 00:03:00,050
And either fix the next hop or simply remove it and rely on the default route here.

43
00:03:00,840 --> 00:03:02,820
So Ken wrote a one ping.

44
00:03:05,220 --> 00:03:06,900
The loopback of router three.

45
00:03:07,230 --> 00:03:07,590
Okay.

46
00:03:07,590 --> 00:03:09,390
The pings are still failing.

47
00:03:10,500 --> 00:03:12,930
Let's do a trace to that address.

48
00:03:14,800 --> 00:03:17,290
The packet gets sent to.

49
00:03:18,690 --> 00:03:22,140
Brought to, but then goes nowhere else.

50
00:03:22,380 --> 00:03:26,580
So it doesn't look like it gets any further based on that output.

51
00:03:27,420 --> 00:03:32,400
So Ken wrote it to ping the loopback of router three.

52
00:03:34,910 --> 00:03:36,020
Yes, it can.

53
00:03:36,350 --> 00:03:40,820
So rather to keeping the loop back over rather three, but rather one comping the loop back of rather

54
00:03:40,820 --> 00:03:41,420
three.

55
00:03:42,530 --> 00:03:43,570
So on rather three.

56
00:03:43,580 --> 00:03:44,900
Let's do a debug.

57
00:03:46,450 --> 00:03:53,200
And check if the traffic is actually getting to router three from router one and we can see that it

58
00:03:53,200 --> 00:04:01,300
is so we can see that the pings are arriving at rather three, but it looks like the reply is not getting

59
00:04:01,300 --> 00:04:03,130
back to right of one.

60
00:04:03,400 --> 00:04:07,570
So rather three received an echo request from 2001.

61
00:04:07,570 --> 00:04:08,500
Colon one colon.

62
00:04:08,500 --> 00:04:13,600
Colon one which is rather one destination is the loopback of router three.

63
00:04:13,900 --> 00:04:17,890
So the echo reply is sent, but it's not getting back again.

64
00:04:18,370 --> 00:04:20,470
So let's turn off debugging.

65
00:04:21,820 --> 00:04:25,330
And that's to a debug IPV six packet.

66
00:04:25,360 --> 00:04:29,320
Now, in the real world, you need to be very careful doing this.

67
00:04:30,310 --> 00:04:34,450
I'm going to send a single packet and let's see what happens.

68
00:04:34,750 --> 00:04:38,320
Again, be very careful doing this in the real world.

69
00:04:38,320 --> 00:04:39,790
You'll get a lot of output.

70
00:04:40,510 --> 00:04:46,630
Even in the small network, if we don't turn off debugging, we might get a lot of output on the console.

71
00:04:46,660 --> 00:04:52,660
So there's the debug I sent a single ping from router one two out of three.

72
00:04:53,510 --> 00:04:56,540
We got a destination lookup for that.

73
00:04:56,780 --> 00:05:01,850
The router sees that as a local network connected to the loopback.

74
00:05:02,030 --> 00:05:03,560
So that looks good.

75
00:05:03,860 --> 00:05:09,920
But notice here IPV six forward no router to destination 2001.

76
00:05:09,920 --> 00:05:10,910
Colon one colon.

77
00:05:10,910 --> 00:05:21,470
Colon one source is the loopback of rudder three destination is the gigabit zero zero interface of router

78
00:05:21,470 --> 00:05:30,380
one and we told that there's no valid route so it doesn't look like router three knows how to get back

79
00:05:30,380 --> 00:05:40,520
to rata one so show IPV six route is there raft in the routing table to get back to rata one and the

80
00:05:40,520 --> 00:05:41,750
answer is no.

81
00:05:41,780 --> 00:05:52,850
We have this static route which would allow router three to ping the loopback of router one, but it

82
00:05:52,850 --> 00:05:55,880
can't ping 2001.

83
00:05:56,360 --> 00:06:04,640
So what we need to do is add a static route to 2001 colon one, colon colon zero.

84
00:06:04,640 --> 00:06:05,870
Slash 64.

85
00:06:05,930 --> 00:06:07,940
And send that to.

86
00:06:08,330 --> 00:06:10,190
Rata to.

87
00:06:11,480 --> 00:06:12,860
Now let's do the ping again.

88
00:06:12,890 --> 00:06:14,840
Notice the ping succeeded.

89
00:06:17,450 --> 00:06:21,710
And without using the repeat command, the pings now succeed.

90
00:06:22,100 --> 00:06:29,840
So we can get to the loopback of router three and we can get to the physical interface of router three.

91
00:06:30,110 --> 00:06:32,090
So be careful with pings.

92
00:06:32,120 --> 00:06:35,870
This applies to both IP version four and IP version six.

93
00:06:36,110 --> 00:06:42,110
Just because I can send traffic to you doesn't mean that you know how to send traffic back to me.

94
00:06:42,200 --> 00:06:47,570
Both sides need routes in the routing table to enable two way communication.

95
00:06:48,050 --> 00:06:49,480
I hope you enjoyed this video.

96
00:06:49,490 --> 00:06:52,310
If it was of benefit to you, please like it.

97
00:06:52,400 --> 00:06:54,980
And please subscribe to my YouTube channel.

98
00:06:55,130 --> 00:06:57,380
I wish you all the very best.