Join Mark Jacob for an in-depth discussion in this video Introducing dynamic routing protocols, part of Introduction to Routing.
-Hi. Today we're going to be talking about dynamic routing protocols. Perhaps you are moving up from static routing, which is sufficient in a small environment, but it's kind of like having training wheels, and there's that one day we just want to rip those things off, and explore the big, bad world. That's what we're going to be doing today. We're going to be talking about dynamic routing protocols. So if you have routers in your organization, they can learn about remote destinations, do their own path determination, and if some typology change occurs, they can make a decision without bothering you as to how to handle it. So the main ones you want to be concerned about, especially if you're considering certification, are Distance Vector protocols and Link State protocols. So, if you want to kind of add to the list here, I started off with just the headings. Want to add to the list, I'll say Distance Vector, the old stand-by, which almost nobody uses anymore anyway, but at least it's there. RIP is a distance vector routing protocol. It turns out, in fact if you want to put another one here that should be listed right along with the dodo birds, IGRP. Even Cisco doesn't support that one anymore, and EIGRP, which used to be, up until 2013, Cisco proprietary. It is no longer Cisco proprietary. They released it to open source. But those are examples of distance vector routing protocols. How about Link State? Well, if you're familiar with IS-IS, Intermediate System-Intermediate System, that is a link state routing protocol. And, you're not really expected to know that one, but OSPF. That one you definitely want to know about. So, how do you categorize, or what indicates whether a protocol is distance vector or link state? Well, let's start with the distance vector. First of all, who does a distance vector routing protocol listen to to get its information? Well, I'm going to start on this side, and I'll put DV here and LS here, kind of indicate which is which. But who does it listen to? I'm going to put "Directly "Connected "Neighbors." That's who distance vector protocols listen to. So whether it's RIP, EIGRP, doesn't matter. Who am I connected to, who am I talking to? That's the one that I'm getting my routing update. That's why a lot of times people call it routing by rumor, because you only know what your neighbor has told you. Let's see. Another thing, in fact, if you want to consider what does, since we have it up, RIP, what does it care about as far as making a determination of what is a good path? RIP cares about one thing, and one thing only. HOPS. How many HOPS away is it, and kind of a generic way to think about it, each router is considered a HOP, and if it's three HOPS away, that's better than a route that's five HOPS away, regardless of how fast the links are. Want to let you know right away, RIP is not particularly good because most people do care about link speed. Just like if you're looking at a map and trying to pick a destination. I can go this road, which might look good because it's wide on the map, but it's 5 o'clock and it's rush hour, and it's a parking lot. Or I can go this skinny little road, but it actually goes faster because everybody's over stuck on the freeway. So mindset there. Link state is kind of different. Link state doesn't just listen to directly connected neighbors. Link state knows about the entire typology of the whole network. So link state tends to have more accurate information. Now, clearly we're just brushing the surface on these, just to get an idea, an introduction to these topics, but a good way to think about the difference between the two. Let's say that you are in Phoenix, AZ. And you want to go to Disney Land. Well, if you have an arrangement that you could compare to a distance vector, that would be like you kind of know that Disney Land is west of here. And if I get on I-10 and start heading west, eventually I'm going to see a road sign that tells me that Disney Land is getting closer. And that's how, kind of a distance vector works. You don't have a full map, the entire typology network, but if the next HOP is not directly touching where you're going, at least it can get you closer. Link state, on the other hand, that's kind of like saying, "Hey, I have a map that shows me every single "possible path, every single destination. "And if I want to go to Disney Land, for example, "I can look at that, and directly from my house, plot a " course all the way to Disney Land." So that's kind of, if you're looking at the 50,000 foot view, Link state tends to have more information, make more informed decisions than distance vector protocols. Nevertheless, both of these are widely used. In fact, now that EIGRP is no longer proprietary, it's probably going to be making even more inroads into companies' networks. But this gives you just a brief description of dynamic routing protocols. Coming to understand them can certainly make your job as a network admin easier.