The calculation of a routing metric is different across operating systems and routing protocols. In this video, you’ll learn some of the characteristics that our routing protocols use to prioritize one route over another.
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So far we’ve looked at routing tables and the method that our routers use to determine what the next best hop is going to be. And one of the things that you’ve seen in a routing table is something called a routing metric. This can be very useful if a router is trying to make a decision on how to get to a location and it has a number of options.
If there are three different routes to a location, it needs to make a determination on which one of those is really going to be the best route. And routing metrics is a very good way to do that. There are many different ways to calculate a routing metric, and different routing protocols use different methods. That’s because different routing protocols might take different things into account.
The Routing Information Protocol, for instance, uses hop counts. That’s all that it uses. That’s the only determination that it makes to be able to set a metric for what the best route might be.
EIGRP, he used a metric between 0 and 4,294,967,295. There’s a very wide range of metrics that you can have. That is a very granular dynamic routing protocol.
In Windows– in the operating system itself– you will see metrics somewhere between one and 9999. And that’s one of the ways that Windows is able to determine what the best route to a location may be. There’s many different characteristics that may go in to determining what the final metric is in a route.
And here’s an example of some of the more common ones. For Routing Information Protocol and other routing protocols as well, you might look at hop count. One interesting routing metric might be something like the speed of the network. If we know that one particular path is faster than another, then we’ll want to take the one that is the fastest route to our destination.
Another characteristic might be throughput, load, or link utilization. We can take into account just how busy a network might be, and that might help us make a determination on what the better route might be to take for our traffic. Our routing protocols might also consider other things such as MTU or path reliability, or packet loss or latency. That way we can determine how big the packets are that we can put through the network and how likely is it that that traffic is going to get to the other side.
Not all routing protocols examine all of these particular characteristics. Some routing protocols only consider one of these. Some routing protocols consider many different characteristics. So you’ll need to look at the specifics of the dynamic routing protocol to understand how is it making the decision on how to get from point A to point B, and then how is it calculating the metric based on those characteristics.