Original subtitles

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So router 1 can ping the loopback of router 3

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but notice the ping was sent from 10.1.1.1 to router 3.

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With ping you can specify the source interface of a ping

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so I could say loopback 0 or specify the source IP address.

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So let’s specify loopback 0

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in other words, pings are being sent from the loopback of router 1 to router 3

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but the pings are failing because router 3 is receiving a ping

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from an IP address of 1.1.1.1

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sh run int loopback0

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this router has this IP address configured on loopback0

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and we are telling the router to ping the loopback of router 3

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using the IP address as configured on loopback 0.

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We can see that in the debug on router3

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does router 3 have that route in its routing table?

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The answer is no, so debug ip packet do the ping again

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what we can see is that it’s unroutable.

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Router 3 doesn’t know how to get back to 1.1.1.1

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so we need to configure the loopback of router 1 on router 3

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and this is the problem

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how many routes do you need to configure

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on this routers to allow for full communication?

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A lot of static routes need to be configured

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to allow full connectivity between these routers.

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So sh run | include route on router 3

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shows me that I have 1 static route configured.

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So I need to configure another static route 1.1.1.1

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and that’s available from router 3 points of view via 10.1.2.1

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from router 3 points of view to get to this loopback

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it needs to forward traffic via this IP address.

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However, the ping is still failing, we can see a message on router 3

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saying that it receives a message from 10.1.2.1

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stating that this address is unreachable.

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So in other words

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router 1 is sending traffic from this loopback interface

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to this loopback interface

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and it gets successfully to router 3.

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Router 3 tries to route it back to router 2

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but router 2 is saying host unreachable.

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In other words, router 2 doesn’t have a route to 1.1.1.1

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which as we can see in the routing table isn’t there.

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So we have to configure a static route

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on router 2 to the loopback of router 1 via 10.1.1.1

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does the ping work now? Yes, it does.

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so ping succeeds from the loopback of router 1

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to the loopback of router 3 because router 2 now knows

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about the loopback of router 3 as well as the loopback of router 1.

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Are we finished?

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show ip route, so router 1 kind of looks right

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let’s do a show run, show run | include route

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Router 1 has 3 static routes in the routing table.

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1 for this network, 1 for this network and 1 for this network

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so that looks good. Router 2 show ip route

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router 2 only has a static route to the loopback of router 1

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and loopback of router 3 which is correct for the network shown in the diagram.

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What about router 3? show ip route

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it has a static route to the loopback of router 1

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it has a static route to 10.1.1.0

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but it doesn’t have a static route to the loopback of router 2

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I'll just turn off debugging

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and then try and ping the loopback of router 2

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what you’ll notice is the pings fail.

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So what I need to do is configure a route

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to the loopback of router 2 via the next hop 10.1.2.1

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so router 3 can now ping the loopback of router 2

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it can ping the loopback of router 1 that’s good

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router 1 can ping the loopback of router 2

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and the loopback of router 3 I'll turn debugging off on router 2

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it can ping the loopback of router 1 and the loopback of router 3.

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now I did add some extra networks

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show ip route on router 1

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shows me that I added 10.1.10.0 as well as 1.1.1.2

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so can router 2 ping 1.1.1.2 and the answer is no

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in the routing table of router 2

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I only have a static route to 1.1.1.1

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so I would need to add another route for 1.1.1.2

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so I could type IP route 1.1.1.2/32 mask 10.1.1.1

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and now I’ll be able to ping 1.1.1.2

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now do I have to use explicit mask as per

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the subnets configured on interfaces and the answer is no.

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I could as an example remove this static route

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and change that to something like this

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so in other words, I’m going to match 10.1.1.1.0

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and anything in that range is going to be forwarded to 10.1.2.1

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so ping 1.1.1.1 that works and 1.1.1.2 also works

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you need to be careful however doing that

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because this doesn’t just match those 2 networks

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it matches anything in the range 1.1.1.0

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but in this case based on our topology, I can do that

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router 1 also has this additional network that I added

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so I need to configure that network as well on router 2

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as well as I'll just copy this to make it easier, as well as router 3

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and you need to be careful doing copying and pasting like I’ve just done

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because that should be 2.1 on this router.

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So ping 10.1.10.1 ping works ping 10.1.10.1

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which is the loopback to IP address configured on router 1.

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So here’s the problem, we configured a very small network

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but we configured 3 static routes on router 1

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we've configured 4 static routes on router 2

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and we've configured 4 static routes on router 3

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that’s 11 routes just to get this network working

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it would have been told if I hadn’t use a summary route on router 3

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that's a lot of work for very small network

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and that’s 1 of the problems with static routes, it’s a lot of work

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to configure this routes and you the person that has to configure them.

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Dynamic routing protocols allow routes to be automatically learned

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and adjusted so the work is shifted from your shoulders to the routers.

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The routing protocols do the heavy lifting

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rather than you having to do all this manual configuration.