Router configuration practice: External prefixes (1)

Throughout this series of lectures, We have thoroughly examined the necessary settings for providing basic connections for the entire network. Now, we should have a basic understanding of how to configure important components from the edge layer to the core. This week, I will focus on adding External prefixes, such as static routes to your new OSPF (Open Shortest Path First Protocol) network, it also describes how to manage these routes when these routes pass through each layer.

External prefixes

To send data from one end of your network to the other end, each layer-3 network device along this path must have information on both ends. In this series of lectures, I have introduced you how to set up OSDF on your network devices. This setting allows the prefix/route information on the peer end of your entire network broadcast end.

But what if you want to add another network? The concept of routing policy is something that every engineer should know. At least he can answer this question. The external prefix is a route to the destination. This is not learned through the domain name protocol in your network. It is embedded from the outside into the routing domain name. Simply put, to add another network, you must re-allocate routes to your domain name. In this process, a route is created and marked as an external route by default. However, its attributes are different from those of internal routes. Review the network design using the following charts.

Let's make a brief assumption. There is a new network request that requires you to install a new device in the newly created OSPF network (as shown in. This problem is that these devices do not support OSPF. Of course, OSPF is the protocol you use to broadcast prefix information throughout the network.

Common situation

This is a common problem in many networks, usually related to the installation of firewalls or untrusted network devices. The chart below illustrates this situation.

In this chart, the FW-1 has a network (172.16.11.0/24) behind it, and it must be able to access the network behind the FW-2 (172.16.10.0/24. Remember that neither device supports OSPF, and each device on the path between the two firewalls must know each network. There are several ways to add a prefix to your network. The first method is to install a static route on D1 and D4 and re-allocate the static route to your OSPF domain name.

Configure the firewall Interface

D1(config)#interface g4/1 D1(config-if)#ip address 150.1.1.37 255.255.255.252 D4(config)#interface g4/1 D4(config-if)#ip address 150.1.1.41 255.255.255.252

Configure Static Routing

Configure the static routes D1(config)#ip route 172.16.11.0 255.255.255.0 150.1.1.38 D4(config)#ip route 172.16.10.0 255.255.255.0 150.1.1.42

I have not shown it here. However, do not forget to configure the static default address 0.0.0.0 and set the same default address for the firewall itself. Note that I have also defined the next hop address for the static route configuration. Another option is to define a physical interface. This option is not recommended.