Original subtitles

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To enable connectivity in this network

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we can configure static routes

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so on router 1, as an example, conf t ip route

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and notice we have various options, destination prefix, profile, static and VRF

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it’s important that you know the options for static route.

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so as an example, the destination prefix

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or destination network that I want to configure is 10.1.2.0

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and the reason that I want to use 10.1.2.0

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is because this is a /24 network.

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Now you can implement summarization of your static routes

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but for now use the exact mask, question mark is destination prefix mask.

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so 255.255.255.0 because this is a /24 question mark

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I can now specify the next hop router or an outgoing interface

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when setting up routing look at it from routers point of view.

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From router's 1 point of view, what is the next hop IP address

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that he uses to get to this network?

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In other words, when router 1 sends traffic out of this interface

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what’s the next IP address that it's going to hit?

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it's going be this IP address 10.1.1.2

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So if router 1 was trying to get to a network somewhere on the right here

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the next hop would still be 10.1.1.2

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because that’s the next hop IP address that the router is forwarding traffic to.

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So just think what’s the next IP address that going to be hit

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when the router forwards the traffic out of an interface

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that’s your next hop IP address.

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So, in this case, it's 10.1.1.2 we can specify various options here

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such as an administrative distance make the route permanent

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and other options but for now that’s all I’m going to specify.

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Notice we’ve got the option carriage return

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and that’s what we’ve used now

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in other words, routes has been added to the routing table.

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Let’s confirm that so sh ip route

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shows us that this network 10.1.2.0

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has been added to the routing table as a static route.

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S means static, route is available via 10.1.1.2

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in other words, this IP address.

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So can we ping 10.1.2.2? Ping 10.1.2.2 pings failed

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but we are getting output on router 3

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so on router 3, it’s sending an echo reply back

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from 10.1.2.2 to destination 10.1.1.1

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so in other words, the traffic is getting from router 1 to router 3

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but it’s not getting back again.

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And the reason for that is router 3 doesn’t have a route back to router 1.

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We can see that by using the command sh ip route

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back to 10.1.1.0. as an example, if I try and ping 10.1.1.1

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the IP address of this router, router 1

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in network 10.1.1.0/24 pings failed

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and we can use the command debug ip packet

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to show us that the router doesn’t know how to get to that network.

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The traffic is unroutable.

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So how do we fix this? Well, we need to create a static route back again.

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So IP route 10.1.1.0 with the mask /24

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and in this case we're going to use the next hop IP address 10.1.2.1

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now you can use the local outgoing interface

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but that’s not recommended on Ethernet interfaces

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only do that on point to point links such as serial interfaces on Ethernet

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use a next hop IP address not the local outgoing interface

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so does the ping work now?

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Yes it does and you can see a lot of output

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so let’s turn off debugging

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un all or undebug all turns off debugging

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I’ll only enable ICMP

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so debug ip icmp

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we can see the echo replies are sent and the pings succeed

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in other words, the traffic got from router 1 to router 3 and arrive back again.