1 00:00:00,000 --> 00:00:05,000 So router 1 can ping the loopback of router 3 2 00:00:05,000 --> 00:00:11,000 but notice the ping was sent from 10.1.1.1 to router 3. 3 00:00:11,000 --> 00:00:17,000 With ping you can specify the source interface of a ping 4 00:00:17,000 --> 00:00:23,000 so I could say loopback 0 or specify the source IP address. 5 00:00:23,000 --> 00:00:27,000 So let’s specify loopback 0 6 00:00:27,000 --> 00:00:32,000 in other words, pings are being sent from the loopback of router 1 to router 3 7 00:00:32,000 --> 00:00:38,000 but the pings are failing because router 3 is receiving a ping 8 00:00:38,000 --> 00:00:41,000 from an IP address of 1.1.1.1 9 00:00:41,000 --> 00:00:45,000 sh run int loopback0 10 00:00:45,000 --> 00:00:51,000 this router has this IP address configured on loopback0 11 00:00:51,000 --> 00:00:57,000 and we are telling the router to ping the loopback of router 3 12 00:00:57,000 --> 00:01:02,000 using the IP address as configured on loopback 0. 13 00:01:02,000 --> 00:01:05,000 We can see that in the debug on router3 14 00:01:05,000 --> 00:01:09,000 does router 3 have that route in its routing table? 15 00:01:09,000 --> 00:01:18,000 The answer is no, so debug ip packet do the ping again 16 00:01:18,000 --> 00:01:25,000 what we can see is that it’s unroutable. 17 00:01:25,000 --> 00:01:30,000 Router 3 doesn’t know how to get back to 1.1.1.1 18 00:01:30,000 --> 00:01:36,000 so we need to configure the loopback of router 1 on router 3 19 00:01:36,000 --> 00:01:38,000 and this is the problem 20 00:01:38,000 --> 00:01:40,000 how many routes do you need to configure 21 00:01:40,000 --> 00:01:43,000 on this routers to allow for full communication? 22 00:01:43,000 --> 00:01:46,000 A lot of static routes need to be configured 23 00:01:46,000 --> 00:01:49,000 to allow full connectivity between these routers. 24 00:01:49,000 --> 00:01:54,000 So sh run | include route on router 3 25 00:01:54,000 --> 00:01:58,000 shows me that I have 1 static route configured. 26 00:01:58,000 --> 00:02:04,000 So I need to configure another static route 1.1.1.1 27 00:02:04,000 --> 00:02:11,000 and that’s available from router 3 points of view via 10.1.2.1 28 00:02:11,000 --> 00:02:14,000 from router 3 points of view to get to this loopback 29 00:02:14,000 --> 00:02:17,000 it needs to forward traffic via this IP address. 30 00:02:17,000 --> 00:02:30,000 However, the ping is still failing, we can see a message on router 3 31 00:02:30,000 --> 00:02:34,000 saying that it receives a message from 10.1.2.1 32 00:02:34,000 --> 00:02:37,000 stating that this address is unreachable. 33 00:02:37,000 --> 00:02:39,000 So in other words 34 00:02:39,000 --> 00:02:43,000 router 1 is sending traffic from this loopback interface 35 00:02:43,000 --> 00:02:45,000 to this loopback interface 36 00:02:45,000 --> 00:02:48,000 and it gets successfully to router 3. 37 00:02:48,000 --> 00:02:52,000 Router 3 tries to route it back to router 2 38 00:02:52,000 --> 00:02:54,000 but router 2 is saying host unreachable. 39 00:02:54,000 --> 00:03:00,000 In other words, router 2 doesn’t have a route to 1.1.1.1 40 00:03:00,000 --> 00:03:04,000 which as we can see in the routing table isn’t there. 41 00:03:04,000 --> 00:03:07,000 So we have to configure a static route 42 00:03:07,000 --> 00:03:16,000 on router 2 to the loopback of router 1 via 10.1.1.1 43 00:03:16,000 --> 00:03:20,000 does the ping work now? Yes, it does. 44 00:03:20,000 --> 00:03:25,000 so ping succeeds from the loopback of router 1 45 00:03:25,000 --> 00:03:29,000 to the loopback of router 3 because router 2 now knows 46 00:03:29,000 --> 00:03:34,000 about the loopback of router 3 as well as the loopback of router 1. 47 00:03:34,000 --> 00:03:36,000 Are we finished? 48 00:03:36,000 --> 00:03:44,000 show ip route, so router 1 kind of looks right 49 00:03:44,000 --> 00:03:47,000 let’s do a show run, show run | include route 50 00:03:47,000 --> 00:03:52,000 Router 1 has 3 static routes in the routing table. 51 00:03:52,000 --> 00:03:54,000 1 for this network, 1 for this network and 1 for this network 52 00:03:54,000 --> 00:03:58,000 so that looks good. Router 2 show ip route 53 00:03:58,000 --> 00:04:04,000 router 2 only has a static route to the loopback of router 1 54 00:04:04,000 --> 00:04:10,000 and loopback of router 3 which is correct for the network shown in the diagram. 55 00:04:10,000 --> 00:04:13,000 What about router 3? show ip route 56 00:04:13,000 --> 00:04:18,000 it has a static route to the loopback of router 1 57 00:04:18,000 --> 00:04:23,000 it has a static route to 10.1.1.0 58 00:04:23,000 --> 00:04:27,000 but it doesn’t have a static route to the loopback of router 2 59 00:04:27,000 --> 00:04:29,000 I'll just turn off debugging 60 00:04:29,000 --> 00:04:33,000 and then try and ping the loopback of router 2 61 00:04:33,000 --> 00:04:35,000 what you’ll notice is the pings fail. 62 00:04:35,000 --> 00:04:40,000 So what I need to do is configure a route 63 00:04:40,000 --> 00:04:47,000 to the loopback of router 2 via the next hop 10.1.2.1 64 00:04:47,000 --> 00:04:52,000 so router 3 can now ping the loopback of router 2 65 00:04:52,000 --> 00:04:57,000 it can ping the loopback of router 1 that’s good 66 00:04:57,000 --> 00:05:00,000 router 1 can ping the loopback of router 2 67 00:05:00,000 --> 00:05:05,000 and the loopback of router 3 I'll turn debugging off on router 2 68 00:05:05,000 --> 00:05:12,000 it can ping the loopback of router 1 and the loopback of router 3. 69 00:05:12,000 --> 00:05:14,000 now I did add some extra networks 70 00:05:14,000 --> 00:05:17,000 show ip route on router 1 71 00:05:17,000 --> 00:05:25,000 shows me that I added 10.1.10.0 as well as 1.1.1.2 72 00:05:25,000 --> 00:05:30,000 so can router 2 ping 1.1.1.2 and the answer is no 73 00:05:30,000 --> 00:05:33,000 in the routing table of router 2 74 00:05:33,000 --> 00:05:39,000 I only have a static route to 1.1.1.1 75 00:05:39,000 --> 00:05:48,000 so I would need to add another route for 1.1.1.2 76 00:05:48,000 --> 00:05:56,000 so I could type IP route 1.1.1.2/32 mask 10.1.1.1 77 00:05:56,000 --> 00:06:02,000 and now I’ll be able to ping 1.1.1.2 78 00:06:02,000 --> 00:06:08,000 now do I have to use explicit mask as per 79 00:06:08,000 --> 00:06:17,000 the subnets configured on interfaces and the answer is no. 80 00:06:17,000 --> 00:06:23,000 I could as an example remove this static route 81 00:06:23,000 --> 00:06:29,000 and change that to something like this 82 00:06:29,000 --> 00:06:41,000 so in other words, I’m going to match 10.1.1.1.0 83 00:06:41,000 --> 00:06:47,000 and anything in that range is going to be forwarded to 10.1.2.1 84 00:06:47,000 --> 00:06:51,000 so ping 1.1.1.1 that works and 1.1.1.2 also works 85 00:06:51,000 --> 00:06:55,000 you need to be careful however doing that 86 00:06:55,000 --> 00:07:00,000 because this doesn’t just match those 2 networks 87 00:07:00,000 --> 00:07:05,000 it matches anything in the range 1.1.1.0 88 00:07:05,000 --> 00:07:09,000 but in this case based on our topology, I can do that 89 00:07:09,000 --> 00:07:13,000 router 1 also has this additional network that I added 90 00:07:13,000 --> 00:07:24,000 so I need to configure that network as well on router 2 91 00:07:24,000 --> 00:07:29,000 as well as I'll just copy this to make it easier, as well as router 3 92 00:07:29,000 --> 00:07:36,000 and you need to be careful doing copying and pasting like I’ve just done 93 00:07:36,000 --> 00:07:41,000 because that should be 2.1 on this router. 94 00:07:41,000 --> 00:07:49,000 So ping 10.1.10.1 ping works ping 10.1.10.1 95 00:07:49,000 --> 00:07:55,000 which is the loopback to IP address configured on router 1. 96 00:07:55,000 --> 00:07:59,000 So here’s the problem, we configured a very small network 97 00:07:59,000 --> 00:08:05,000 but we configured 3 static routes on router 1 98 00:08:05,000 --> 00:08:10,000 we've configured 4 static routes on router 2 99 00:08:10,000 --> 00:08:19,000 and we've configured 4 static routes on router 3 100 00:08:19,000 --> 00:08:22,000 that’s 11 routes just to get this network working 101 00:08:22,000 --> 00:08:27,000 it would have been told if I hadn’t use a summary route on router 3 102 00:08:27,000 --> 00:08:30,000 that's a lot of work for very small network 103 00:08:30,000 --> 00:08:34,000 and that’s 1 of the problems with static routes, it’s a lot of work 104 00:08:34,000 --> 00:08:39,000 to configure this routes and you the person that has to configure them. 105 00:08:39,000 --> 00:08:44,000 Dynamic routing protocols allow routes to be automatically learned 106 00:08:44,000 --> 00:08:48,000 and adjusted so the work is shifted from your shoulders to the routers. 107 00:08:48,000 --> 00:08:51,000 The routing protocols do the heavy lifting 108 00:08:51,000 --> 00:08:56,000 rather than you having to do all this manual configuration.