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These are the user uploaded subtitles that are being translated: 1 00:00:00,000 --> 00:00:05,000 align:middle line:84% In the real world, you would never plug a hub between 2 switches 2 00:00:05,000 --> 00:00:08,000 align:middle line:84% because it will degrade your network dramatically. 3 00:00:08,000 --> 00:00:11,000 align:middle line:84% In this example, we’ve only got the hub in the topology 4 00:00:11,000 --> 00:00:13,000 align:middle line:84% so that we can capture traffic using Wireshark 5 00:00:13,000 --> 00:00:18,000 align:middle line:84% you generally have a direct link between the 2 switches as shown here. 6 00:00:18,000 --> 00:00:21,000 align:middle line:84% In our topology, I've shut that force down 7 00:00:21,000 --> 00:00:23,000 align:middle line:84% to force all traffic to go via the hub 8 00:00:23,000 --> 00:00:26,000 align:middle line:84% so that we can see what’s taking place 9 00:00:26,000 --> 00:00:30,000 align:middle line:84% if I enable this port Spanning Tree will block one of these ports 10 00:00:30,000 --> 00:00:32,000 align:middle line:84% so we won’t be able to see the traffic. 11 00:00:32,000 --> 00:00:35,000 align:middle line:84% So at the moment PC 1 can ping PC 3 12 00:00:35,000 --> 00:00:39,000 align:middle line:84% PC 2 can ping PC 4 but they can't ping each other. 13 00:00:39,000 --> 00:00:45,000 align:middle line:84% So let’s setup switch 1 as our Inter-VLAN router. 14 00:00:45,000 --> 00:00:51,000 align:middle line:84% So on switch 1 sh ip int brief 15 00:00:51,000 --> 00:00:55,000 align:middle line:84% at the moment we have an IP address configured on VLAN 1 and VLAN 2. 16 00:00:55,000 --> 00:00:59,000 align:middle line:84% Now router 1 and router 3 17 00:00:59,000 --> 00:01:06,000 align:middle line:84% are still using the IP addressing of VLAN 1 which is bad practice 18 00:01:06,000 --> 00:01:10,000 align:middle line:84% we can see that so on router 1 sh ip int brief 19 00:01:10,000 --> 00:01:15,000 align:middle line:84% notice the IP address of this device is 10.1.1.1 20 00:01:15,000 --> 00:01:22,000 align:middle line:84% so I'll change that to put it into VLAN 11, so IP 10.1.11.1 21 00:01:22,000 --> 00:01:27,000 align:middle line:84% Just good practice you could keep those IP addresses 22 00:01:27,000 --> 00:01:31,000 align:middle line:84% but it will get confusing when you set up a management VLAN. 23 00:01:31,000 --> 00:01:36,000 align:middle line:84% So I'll just configure it correctly at this point 24 00:01:36,000 --> 00:01:37,000 align:middle line:84% On router 3 currently the IP address is 10.1.1.3 25 00:01:37,000 --> 00:01:54,000 align:middle line:84% so I'll change that to 10.1.11.3 and set up the default gateway 10.1.11.254 26 00:01:54,000 --> 00:01:59,000 align:middle line:84% and then we need to configure VLAN 11 on switch 1 27 00:01:59,000 --> 00:02:05,000 align:middle line:84% so interface VLAN 11, IP address 10.1.11.254 28 00:02:05,000 --> 00:02:12,000 align:middle line:84% I showed that SVI or Switch Virtual Interfaces is up which it is. 29 00:02:12,000 --> 00:02:17,000 align:middle line:84% So can router 1 ping router 3? 30 00:02:17,000 --> 00:02:26,000 align:middle line:84% Just do a test, ping 10.1.11.3 yes, it can. 31 00:02:26,000 --> 00:02:28,000 align:middle line:84% Can it ping router 2? 32 00:02:28,000 --> 00:02:33,000 align:middle line:84% router 2 using this IP address 10.1.2.2 yes, it can. 33 00:02:33,000 --> 00:02:37,000 align:middle line:84% Can it ping router 4 acting as PC 2? 34 00:02:37,000 --> 00:02:40,000 align:middle line:84% So that’s 2.4 35 00:02:40,000 --> 00:02:46,000 align:middle line:84% Let’s just do some troubleshooting 36 00:02:46,000 --> 00:02:50,000 align:middle line:84% so first thing to confirm is, let’s check the interface 37 00:02:50,000 --> 00:02:59,000 align:middle line:84% that interface looks right, let's ping 11.1 38 00:02:59,000 --> 00:03:02,000 align:middle line:84% why is the ping not working? 39 00:03:02,000 --> 00:03:05,000 align:middle line:84% it’s probably because I haven't set up a default gateway on router 4. 40 00:03:05,000 --> 00:03:09,000 align:middle line:84% Let’s confirm that sh ip route 41 00:03:09,000 --> 00:03:15,000 align:middle line:84% there are no default gateways configured, so I'll turn off the IP routing. 42 00:03:15,000 --> 00:03:18,000 align:middle line:84% Before I configure the default gateway 43 00:03:18,000 --> 00:03:22,000 align:middle line:84% let me show you a test that we can do to prove what’s happening. 44 00:03:22,000 --> 00:03:25,000 align:middle line:84% So on router 1, I’m pinging router 4 45 00:03:25,000 --> 00:03:30,000 align:middle line:84% and this debug, debug ip icmp shows us that the traffic hits router 4 46 00:03:30,000 --> 00:03:32,000 align:middle line:84% but it’s not getting back. 47 00:03:32,000 --> 00:03:34,000 align:middle line:84% So we can see that the traffic traverses 48 00:03:34,000 --> 00:03:38,000 align:middle line:84% the network gets here but doesn’t get back again 49 00:03:38,000 --> 00:03:40,000 align:middle line:84% and that allows me to see that 50 00:03:40,000 --> 00:03:42,000 align:middle line:84% it’s because my default gateway is not configured. 51 00:03:42,000 --> 00:03:49,000 align:middle line:84% So IP default gateway 10.1.2.254 on router 4 because it’s in VLAN 2. 52 00:03:49,000 --> 00:03:51,000 align:middle line:84% So once again. 53 00:03:51,000 --> 00:03:53,000 align:middle line:84% This device is in VLAN 11. 54 00:03:53,000 --> 00:04:00,000 align:middle line:84% This device is in VLAN 11, these 2 devices are on VLAN 2. 55 00:04:00,000 --> 00:04:04,000 align:middle line:84% So can router 1 ping router 4? Yes, it can. 56 00:04:04,000 --> 00:04:09,000 align:middle line:84% So let’s have a look at the 802.1Q frames sent. 57 00:04:09,000 --> 00:04:14,000 align:middle line:84% Here’s router 1 pinging router 4 58 00:04:14,000 --> 00:04:16,000 align:middle line:84% and let’s look at the ICMP 59 00:04:16,000 --> 00:04:26,000 align:middle line:84% what you’ll notice is the messages from 10.1.11.1 to 10.1.2.1 60 00:04:26,000 --> 00:04:29,000 align:middle line:84% are actually being sent on VLAN 2 61 00:04:29,000 --> 00:04:32,000 align:middle line:84% and the return traffic is being sent on VLAN 2 62 00:04:32,000 --> 00:04:39,000 align:middle line:84% and that’s because the traffic is being sent from router 1 to switch 1 63 00:04:39,000 --> 00:04:42,000 align:middle line:84% and switch 1 has already doing the Inter-VLAN routing 64 00:04:42,000 --> 00:04:48,000 align:middle line:84% and then forwarding the traffic to switch 2 on VLAN 2 65 00:04:48,000 --> 00:04:54,000 align:middle line:84% so it’s already changing the VLAN information to the VLAN 2 66 00:04:54,000 --> 00:04:56,000 align:middle line:84% when forwarding it to the other switch. 67 00:04:56,000 --> 00:05:02,000 align:middle line:84% when the traffic goes from router 4 to router 1 68 00:05:02,000 --> 00:05:04,000 align:middle line:84% the traffic it's sent here is an untagged frame 69 00:05:04,000 --> 00:05:08,000 align:middle line:84% and then here it's tag as VLAN 2 70 00:05:08,000 --> 00:05:11,000 align:middle line:84% when it hits the switch which is acting as the default gateway 71 00:05:11,000 --> 00:05:15,000 align:middle line:84% it has the Inter-VLAN routing and then forwards it out of its port 72 00:05:15,000 --> 00:05:21,000 align:middle line:84% because it’s in VLAN 11 and the traffic is going to the device in VLAN 11. 73 00:05:21,000 --> 00:05:25,000 align:middle line:84% So hence here we don’t actually see the tagged frames 74 00:05:25,000 --> 00:05:34,000 align:middle line:84% but we can see that by adding a router on a stick to do the Inter-VLAN routing. 75 00:05:34,000 --> 00:05:39,000 align:middle line:84% So what I’ll do is remove the Inter-VLAN routing on switch 1 76 00:05:39,000 --> 00:05:44,000 align:middle line:84% and configure this device as the routing device in the topology 77 00:05:44,000 --> 00:05:51,000 align:middle line:84% and then what we should see is we should see the tag frames hit this router 78 00:05:51,000 --> 00:05:56,000 align:middle line:84% and then the tagging will be changed. 8882