Join Lazaro Diaz for an in-depth discussion in this video Understanding the area number, part of Advanced Topics in Cisco Routing: RIPv2, EIGRP, and OSPF.
- Okay, now that we've looked at the Process ID number, not to be confused with the autonomous systems of EIGRP because they have the same range, completely different. That was or is the Process ID number, that's the same range. Now we get into the areas. So the areas we have to in all our routers have the same area. Again, at what line do we cross to have multiple areas? It's completely up to you. We wrote 50 routers per area.
We do this as we advertise our networks. So we do "network". Now the networks that we have, let me move this real quick. 10.1.1.4 and 192.168.1.0. Okay, so we go "network 192.168.1.0". Now when we're advertising OSPF, we use what's called wildcard masking which will be discussed later in detail, but this is what we need to use. It looks like an inverse subnet mask, 0.0.0.255, and here comes your area, "area ?" Look at those areas.
4.2 billion something areas. That's a lot of areas starting at zero. That's why zero is very important because it is the backbone area, but we are going to put zero. What that means is that all routers that are in area zero will automatically share their routing tables. Now there is a process that they go through. "Hey, are you in the same area? "Hey, do you have the same hellos? "Is authentication the same?" Then they'll start sharing and exchanging what's called link state advertisements because this is a link state routing protocol.
No longer a distance vector 'cause at no time in the previous routing protocols did we put a wildcard mask or a subnet mask or anything of the kind. Here we're being very specific of the networks that we're actually advertising, but the area, the area is crucial. We all must be in the same area whatever numbers that you choose. But, again, the recommendation, or really the requirement is that you have area zero as your first area because it's the backbone area. So let's go ahead and now do the next network.
"network 10.1.1.4". Now this is using a CIDR of 30, so that's going to change. Again, don't be concerned how these numbers are coming up. We'll be discussing this later. But the area, again, zero, and that's it. That's as hard as it gets, all right? But the one thing that I want to point out is you can tell that the areas are the same. Again, the area, all it is, is that all routers are sharing the same routing table, and that area zero is your backbone area that will always be the very first area that you configure.
So there you go. There are your areas.
- Configuring static and default routes
- Understanding dynamic routing
- Issuing verification commands
- Comparing RIPng and RIPv2
- Using RIP timers
- Configuring an EIGRP feasible successor route
- Exploring EIGRP options
- Introducing the OSPF process ID
- Exploring wildcard masking