Which Routing Protocol is Best for You?

routers lit up
Jeremy Hostrup; Network Center, Inc.

Once in a while I get surprised by the amount of static routing left in larger networks, those with more than a couple locations and more than 10 layer 3 devices. Static routing is easy to implement but it can be time consuming to make changes. Another piece that you lose with static routing is the ability to change routes easily if something changes on your network. That is what routing protocols were designed to do, find the best route to a network and install that route in the routing table. There are three main interior routing protocols: RIP, EIGRP, and OSPF. RIP is a routing protocol that I would have thought would be gone by now but they have introduced support for IPv6 so it is trying to stick around. EIGRP is Cisco’s proprietary routing protocol. OSPF is the industry standard routing protocol.

There are many reasons to switch from static routing to a routing protocol. The main reason that I’ve seen is the ease of adding a new subnet to a network. If you were to add a new subnet in a static routing environment, you would need to add that static route to every layer 3 device. That is a time consuming and tedious process. With a routing protocol, you would just add that subnet to the device running the routing protocol that is closest to where that subnet exists and it will propagate through the network. The routing protocol will use its metrics to determine what the best route to get there is. This means that you don’t have to touch every layer 3 device and add the static route.

Another benefit of using a routing protocol is you get automatic failover if you have redundant connections. So let’s assume you have a main office with two connections to a remote office. If you use static routing and one of those connections fail, you would have to either have track statements tied to your static routes to get failover or you would have to get into the remote office router and change the static routes. You would also need to get into the main office router and change those static routes as well. With a routing protocol, you wouldn’t need to do anything, it would detect that the link went down and it would automatically install the other route into the routing table. This also works if you have two internet connections.

 Which routing protocol you use really depends on how your network is configured and what the future plans are. If you plan on having Cisco everything, you would have no problem using EIGRP. If you have SonicWALL firewalls, Brocade layer 3 switches, and Cisco routers, you should probably use OSPF. Each one is configured a bit differently and they choose the best route using different metrics but at the end of the day, if they are implemented correctly, they are both great routing protocols. OSPF, EIGRP, and RIP do play nicely together. For instance, you can have a Cisco router running EIGRP and OSPF and redistribute routes between the two routing protocols.

The one routing protocol I haven’t touched on is BGP. Essentially, BGP is the routing protocol for the Internet. It is a very powerful routing protocol with many, many features but it is usually not advisable to run that protocol inside your network. Because BGP is designed for extremely large networks, it does not failover quickly.

So, if your network has grown to the point where manually adding and removing routes is becoming a time consuming and tedious process, consider moving to a routing protocol like EIGRP and OSPF. It will make management of your network easier and also provide you with automatic failover if a link goes down.