Static routing for Cisco users [Day Two: The good and bad of static routing]

What is static routing good for? And what are its shortcomings? Read on to discover how and when to use this technique.

There are many positive aspects to static routing:

  • There is no overhead for using static routes. With dynamic routes, network bandwidth is used to communicate available networks between routers. With static routes, as the network administrator hard codes these routes on the routers, the routers never need to communicate routing information.
  • Static routes can be easier to configure if you have a small network. Let's say that I have only two routers and need to configure routing between them. I would need to configure only two route statements, one on each router. With a dynamic routing protocol like RIP, I would have to enter two network statements on each router.
  • Static routes could be considered more secure. Because you aren't learning any routes from any other routers over the network, there is no chance that an incorrect or unsecured route will be learned by your router.
  • Static routes don't request any router resources. A dynamic routing protocol like OSPF can require significant resources from the router to calculate the shortest path across the network when there are many routers. However, you wouldn't want to use static routes when there are many routers anyway (see negatives of using static routing).

Negative aspects of static routing

Don't be fooled into thinking that static routing is always the best tool for the job, however. The greatest negative to using static routes is that they don't scale as your network grows. This is because all static routes must be configured manually. Let's say that you have four routers, and you add a new network on one router. For the other three routers to learn about this, you must enter three static routes. That doesn't sound so bad, until you have 400 routers and add one new network. In that case, you would have to enter the static route on the other 399 routers. That is a lot of typing!

When do you use static routes?

  • When you have a small network with fewer than five routers that isn't planning on growing any larger.
  • When you have a medium-sized network where all routers connect back to a single router (hub-and-spoke topology). In this case, you could use a default route on all remote routers and have those routers all go through the host (maybe they all need Internet access). No matter how many networks were added at the host, no more routes would have to be created.
  • When you need to create a route from one router to another device quickly. Perhaps you add a new firewall to your network or maybe you are connecting to a partner's network and don't want to exchange routing protocol traffic with them.

In summary, as a network administrator, you should be familiar with how and when to use static routes. The ip route statement creates a static route. Static routes should be used in limited application but are very necessary in many network configurations.

About the author: David Davis (CCIE #9369, CWNA, MCSE, CISSP, Linux+, CEH) has been in the IT industry for 15 years. Currently, he manages a group of systems/network administrators for a privately owned retail company and authors IT-related material in his spare time. He has written more than 50 articles, eight practice tests and three video courses and has co-authored one book. His Web site is HappyRouter.com.

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