Internet Protocol (IP) routing protocols have one primary goal: to fill the IP routing table with the current best routes it can find. The goal is simple, but the process and options can be complicated. Routing protocols define various ways that routers chat among themselves to determine the best routes to each destination. As networks […]

We’ve discussed several techniques to improve the performance of Distance-Vector (D-V) protocols. With that accomplished, the next thing to do is to examine their scalability. With the D-V protocols, as the size of an internetwork grows, the number of prefixes to be advertised and stored grows, requiring greater bandwidth and RAM. Also, as the number […]

Continuing on with our discussion of improvements to Distance-Vector protocols, we were about to discuss hold down timers. Here’s our topology: Let’s go back to the initial conditions, where the 10.1.0.0/16 subnet was reachable. At that point, we had: R1 sees 10.1.0.0/16 as directly connected (zero hops) R2 sees 10.1.0.0/16 as reachable via R1 (one hop) R3 sees […]

Continuing our discussion of techniques for improving the performance of Distance-Vector routing protocols, imagine that we have a topology consisting of three routers (R1, R2 and R3) in a triangle, with each router directly connected to the other two (a full mesh). R1 also has a directly connected stub route, 10.1.0.0/16, for a total of […]

In this installment, we’ll look at some techniques for improving the performance of Distance-Vector (D-V) routing protocols. As previously discussed, if a routing loop occurs between two routers, the routing updates will bounce between those routers. This is sometimes referred to as “routing feedback”. The metric for the prefix will count up to the maximum […]

The Distance-Vector (D-V) protocols such as RIP work, but they’re not perfect. Let’s imagine that we have two routers (R1 and R2) and three subnets (10.1.0.0/16, 10.2.0.0/16 and 10.3.0.0/16), connected in a string, like this: 10.1.0.0/16  –  R1  –  10.2.0.0/16  –  R2  –  10.3.0.0/16 Once the network has converged, both routers will know the best path to each of the three subnets. Looking specifically […]

In this series, we’ll discuss routing and routing protocols. First, let’s define what we mean by a “route”. In common usage, a “route” is an entry in the IP routing table. You can display the IP routing table (available routes) with the command show ip route. Each entry in the routing table gives the best […]