16.3 Adding a routing protocol

Now we have the IP addresses configured we will have LAN connectivity. We need to configure the routers with a routing protocol to allow access to the DNS server from the PCs. We could do this with static routes, but that would be time consuming and less efficient to manage later. The better solution is to use a dynamic routing protocol. RIP is the simplest routing protocol and uses hops as its metric.

We can start by configuring RIP version 2 on Branch-A’s router. Open the CLI and enter global configuration mode. From here type router rip. This will enter router configuration mode. Then type version 2, allowing us to use classless networks instead of the classful addresses used in version 1. Then we need tell RIP which networks to advertise on. This can be done using the network command. Type network 172.20.16.0and then network 172.20.18.0and also network 172.20.31.252.

To check the configuration of RIP we can use show ip protocols. This command shows us how often updates are sent and when the next update is expected. Also it shows us which interfaces are being used within RIP and some other useful information for troubleshooting if we need it.

Moving to Branch-B, we need to configure RIPng for IPv6 routing. This is done slightly differently compared to the IPv4 version. Start by entering global configuration mode. We need to enable IPv6 routing capabilities on this router. The command is ipv6 unicast-routing. Now we can enable RIPng on the router. The command is ipv6 router rip. Then you type an instance name; I will use RIPng1. This name is only locally significant, but it is easier to use the same name on all devices.

This is where the key difference between IPv4 and IPv6 configuration comes in. You have to add the interfaces to the RIP process and not the network. Therefore, enter the interface. Then add the interface to the RIP process with the command ipv6 rip RIPng1 enable where RIPng1 is the same as the process ID you set previously. Repeat this on all interfaces that need to be included in the RIP process.

Now, on the Central router we will need to configure RIP for both IP versions. First I will setup RIPng. From global configuration mode, use the command ipv6 unicast-routing to turn on IPv6 routing. Then we’re going to use ipv6 router rip RIPng1 to enable RIP on the router. Then we need to go into the interfaces that are being used by RIP and enable RIP on the interface using the command ipv6 rip RIPng1 enable. Repeat this on G0/2: ipv6 rip RIPng1 enable. We can then type exit to get back to global configuration mode.

Now we can start configuring RIP version 2 for IPv4. First we use router rip then upgrade it to version 2 and then add the network statements to advertise RIP. So we need network 172.20.31.252 and network 172.20.32.0.

To check that RIP is working properly and that routers are receiving updates, we can use show ip route to check the routing table to see if there are any RIP routing entries. From the Central router’s point of view, it should have two RIP entries for IPv4 and two RIP entries for IPv6. We can see the two specific routes at the top of the routing table and if we do show ipv6 routewe can see the IPv6 routes at the top of this table as well.

Now we have routing configured on all the routers, all the IPv4 devices should be able to communicate and all IPv6 devices should have connectivity. We will test this later in the session.