Routing tables can be created automatically or through manual configurations. In this video, you’ll learn the differences between static and dynamic routing.
<< Previous: Routing MetricsNext: Link State, Distance Vector, and Hybrid Routing >>
In our previous videos, we’ve looked at routing tables and next hops. And we’ve had a lot of discussions about dynamic routing protocols and static routing. In this video, we’ll look at the difference between those two, and we’ll examine the advantages and disadvantages between using dynamic routing and static routing.
A router’s job is to look at the traffic coming inbound, determine where the destination is, and then make a decision on where that traffic is going based on a routing table. And if the router can do all of this automatically, update the routing table, and keep everything in sync, then it is a dynamic routing protocol. This is something that is done without any human intervention.
If something changes on the network, you don’t have to manually reconfigure anything inside of your routers. The dynamic routing protocol is going to do all of that for you. It takes relatively little to get a dynamic routing protocol running on your router.
You configure your router with all of your different interfaces in the subnet mask to those interfaces. You tell the router that you’d like to use a particular routing protocol, and you set some configurations to use that particular routing protocol, and the router takes it from there. It uses that dynamic routing protocol to communicate on the network to other routers, and they all began communicating between each other. And in that way, they’re able to keep track of any changes that might be occurring and to make sure that all of the traffic is able to get all the way through the network.
If there is a problem, these routers all have to converge. They converse amongst each other that a route is no longer available. Perhaps an entire router has been disconnected from the network. So the routers all communicate and decide now what is the new next best hop going to be. And then all of the routers update everyone else with what the new set of routes is going to be.
The time that it takes for that to occur may be a number of minutes. It might be a number of seconds. Convergence is generally something very specific to the dynamic routing protocol that you’re going to use. So that’s going to be one of the considerations you take into account when you decide what is the dynamic routing protocol that I need to use.
And of course, there’s many options available. You can decide on RIP, RIP Version 2, OSPF, EIGRP, BGP. And one of those routing protocols is going to fit best for what you need inside of your organization.
With static routing, there’s no protocols. There’s no routers talking to each other. There’s nothing done automatically either. You as the human being go into your router, you configure what the routes are, and you’re able to make the determination manually and set those permanently inside of the router.
This can be something that might be relatively simple or it may take a number of entries and have a very complex default set of routes that you’re configuring statically inside of your router. Every network is a little bit different, but certainly the difficulty of this might help you determine on whether static routing is the right thing to do for your network, or maybe it should be dynamically routed. You may think that static routing is something that really only works if you have a small network. But even in some of the largest networks, you’ll find that static routing might be a very good alternative.
In some cases it may be a simple configuration with just a few entries in a routing table. And in this way, the administrator of the network has complete control over where the traffic is going, and there’s no question that anything might change dynamically. Here’s an example of how you might configure your router for static routing.
We’ll decide that we would like all internet traffic which would be all of the traffic that matches 0.0.0.0/0. So this is all of our traffic by default is going to be sent out port 1 to the next hop of 10.1.1.1. Now of course, we have traffic on the inside of our network. So we might have another route set that says, if anything is going to 10.1.2.0, which is inside of our network with a 24-bit subnet, send all of that traffic out port 2, which will be our inside interface, to the next hop of 10.1.2.20. So by simply setting two static routes inside of our router, we can now determine where traffic is going to go.
One of the challenges with static routing is we have to think about outages. We might have multiple routes going out of a router, and we’ll set some metrics higher than the other. That way, if we lose our primary route, everything can begin routing through another link.
In fact, in those cases there’s almost no convergence time because your static routes know exactly what to do if it loses a connection. And in that scenario, you’re already building out the redundancy all statically with your static routing, and you’re not relying on a dynamic routing protocol to do any type of convergence.