1 00:00:09,650 --> 00:00:16,309 This is one of multiple videos that demonstrate troubleshooting scenarios in campus environments. 2 00:00:16,480 --> 00:00:23,510 In this typology I have four switches configured switch one and switch to switches switch three and 3 00:00:23,510 --> 00:00:26,060 switch 4 are access switches. 4 00:00:26,330 --> 00:00:32,250 Now to keep the topology simple I haven't got cross-connects configured here or 5 00:00:32,390 --> 00:00:40,130 additional access switches. In my CCNA course, I show you a larger topology but for this troubleshooting 6 00:00:40,160 --> 00:00:42,430 video we'll keep it simple. 7 00:00:42,470 --> 00:00:50,750 We've been told that PC 1 in this network is not able to ping PC 2 in this topology I'm using routers to simulate 8 00:00:50,780 --> 00:00:51,810 PCs. 9 00:00:51,810 --> 00:01:04,980 So let's test that, can router 1 or PC 1 ping 10 132? 10 00:01:05,050 --> 00:01:07,650 So it looks like the pings are failing. 11 00:01:09,830 --> 00:01:18,950 PC 1 is in VLAN 2 and PC 2 is in VLAN 3, show IP route routing is disabled on this router 12 00:01:19,010 --> 00:01:24,660 but it does have a default gateway of 10.1.2.254. 13 00:01:24,700 --> 00:01:32,460 So we should be able to ping this default gateway, so ping 10.1.2.254. 14 00:01:32,920 --> 00:01:33,610 Yes, we can. 15 00:01:33,610 --> 00:01:36,340 Can we ping VLAN 3 on the default gateway? 16 00:01:36,340 --> 00:01:37,470 Yes, we can. 17 00:01:37,780 --> 00:01:42,850 So PC 1 can get to the default gateway. 18 00:01:42,850 --> 00:01:50,450 What about PC 2? See here's router 2 acting as PC 2, show IP interface brief. 19 00:01:50,800 --> 00:01:58,670 We have 10.1.3.2 configured show IP route default gateways 10.1.3. 20 00:01:58,670 --> 00:01:59,910 254. 21 00:02:00,070 --> 00:02:04,360 So can we ping that default gateway? 22 00:02:04,550 --> 00:02:07,180 Looks like we can't. 23 00:02:07,190 --> 00:02:13,800 So there seems to be a problem somewhere between PC 2 and switch 1. 24 00:02:14,240 --> 00:02:19,730 Let's check on switch 4 connected to PC 2. 25 00:02:19,810 --> 00:02:26,730 So this is switch 4 show IP interface brief. 26 00:02:26,920 --> 00:02:33,200 It's got an IP address of 10 114 ping 10.1.1.254 27 00:02:33,550 --> 00:02:35,070 that works. 28 00:02:35,200 --> 00:02:38,340 That is the default gateway of the switch. 29 00:02:38,620 --> 00:02:45,260 So the switch can ping it's default gateway can it ping 10.1.3.254? 30 00:02:45,460 --> 00:02:46,960 Yes, it can. 31 00:02:46,960 --> 00:02:53,930 So we've established that there's basic connectivity between this switch and the default gateway. 32 00:02:53,950 --> 00:02:57,220 Let's have a look at our trunks, so show interface trunk 33 00:02:59,830 --> 00:03:11,970 trunking is enabled on gigabit 00 that's the interface between switch 4 and switch 2 show CDP neighbors. 34 00:03:12,080 --> 00:03:18,030 We have a relationship to switch to but we've already proven that that works by being able to ping the 35 00:03:18,030 --> 00:03:28,950 default gateway VLANs are allowed across the trunk. Now can you spot a problem already in this topology? 36 00:03:29,040 --> 00:03:33,000 What's the problem based on that single command? 37 00:03:33,090 --> 00:03:37,190 Something's wrong, notice gigabit 38 00:03:37,380 --> 00:03:41,980 00 is a trunk but it's only allowing villans 1 to 2 and 4 39 00:03:42,330 --> 00:03:45,410 but the PCs in VLAN 3. 40 00:03:45,410 --> 00:03:50,340 So let's have a look at the configuration of this gigabit interface. 41 00:03:50,340 --> 00:03:56,310 This interface is configured for trunking and we're not restricting any VLANs but we're only permitting 42 00:03:56,310 --> 00:04:08,010 VLANs 1 to 2 and 4 across the trunk show interface gigabit 01 switch port. 43 00:04:08,020 --> 00:04:09,750 What's wrong here? 44 00:04:10,120 --> 00:04:16,250 Can you spot the problem? We're looking at the output of this interface on this switch. 45 00:04:17,029 --> 00:04:17,940 What's wrong? 46 00:04:19,350 --> 00:04:20,730 Port is enabled 47 00:04:20,910 --> 00:04:29,370 It's set as static access it's configured to use access of helium 3 but notice this key word something's 48 00:04:29,370 --> 00:04:30,510 wrong. 49 00:04:30,510 --> 00:04:34,260 Show run interface gigabit 01. 50 00:04:34,260 --> 00:04:42,960 So the port is correctly configured to be in VLAN 3 but show VLAN brief will show us that there's 51 00:04:42,990 --> 00:04:44,280 a problem. 52 00:04:44,280 --> 00:04:45,710 Can you see the issue? 53 00:04:46,860 --> 00:04:50,580 Where is VLAN 3? 54 00:04:50,640 --> 00:04:52,100 So be careful. 55 00:04:52,320 --> 00:04:58,630 You can have a port configured in a VLAN and not have that VLAN in the VLAN database. 56 00:04:58,680 --> 00:05:03,100 If that's true the port is essentially error disabled it won't work. 57 00:05:03,150 --> 00:05:09,070 No traffic is gonna be sent through that port because it belongs to a rogue VLAN. 58 00:05:09,120 --> 00:05:11,430 This is often the case when VTP is used. 59 00:05:11,430 --> 00:05:19,680 If you delete a VLAN on another switch that update is propagated to other switches in the topology, VTP 60 00:05:19,800 --> 00:05:25,450 removes the VLAN from the VLAN database but doesn't take the port out of the VLAN. 61 00:05:25,470 --> 00:05:31,950 This port is manually configured to be part of VLAN 3 but VLAN 3 doesn't exist in the 62 00:05:31,950 --> 00:05:40,380 VLAN database and hence the switch port command is showing us that that's an inactive VLAN on the 63 00:05:40,380 --> 00:05:41,170 port. 64 00:05:41,490 --> 00:05:43,110 That's a problem. 65 00:05:43,140 --> 00:05:53,960 So show VTP status is configured as a server the switch so let's create VLAN 3 show VLAN 66 00:05:53,970 --> 00:05:55,110 brief. 67 00:05:55,200 --> 00:06:00,970 Suddenly now we see port gigabit 01 configured in VLAN 3 68 00:06:01,350 --> 00:06:06,410 and when we look at the switch port we see that it's in VLAN 3. 69 00:06:06,570 --> 00:06:07,430 That looks good. 70 00:06:07,470 --> 00:06:11,910 So Ken wrote it to ping its default gateway. 71 00:06:12,150 --> 00:06:16,020 We may have to wait a while for things to update. 72 00:06:16,020 --> 00:06:24,910 But notice they the pings started succeeding Ken wrote a one now ping right to acting's PC too. 73 00:06:25,010 --> 00:06:26,180 Yes it can. 74 00:06:26,180 --> 00:06:29,620 So we've successfully result of the issue in this typology. 75 00:06:29,660 --> 00:06:30,920 Be careful. 76 00:06:30,920 --> 00:06:38,270 A port is statically configured in a villain but that requires the villain and the villain database. 77 00:06:38,270 --> 00:06:44,740 When using stented villans if the villain is not in the villain database the port is essentially in 78 00:06:44,960 --> 00:06:48,110 a rogue villain and is not used. 79 00:06:48,110 --> 00:06:51,270 Traffic will not be sent through that port. 80 00:06:51,380 --> 00:06:58,180 So I hope you found this video useful if you did please like it and please subscribe to my YouTube channel. 81 00:06:58,190 --> 00:07:00,760 I wish you all the very best.