IPv6 RIPng dynamic routing

03/14/10 • -1 min

The linked video demonstrates RIPng, our first dynamic routing protocol for IPv6. This is a simple but inefficient routing protocol. The metric is based on number of router hops, with no provision for differentiating between links with drastically different bandwidth (a frame-relay hop has the same cost as a 10-gig-ethernet in RIPng). Each router multicasts its entire routing protocol out each interface every 30 seconds, which wastes router CPU. RIPng routinely takes minutes to reroute around network failures.

RIPng does have the refinements added in RIPv2. For example, it multicasts its route updates. It is also capable of including tags in the route updates.

The big advantage of RIPng is that it is simple to understand. But in production that is not good enough. RIPng is a perfect protocol for a computer science student to implement as a class project due to its simplicity, but having the PBX unreachable for 3-5 minutes while routing reconverges is unacceptable in a business environment.

RIPng does have the refinements added in RIPv2. For example, it multicasts its route updates. It is also capable of including tags in the route updates.

Previous Episode

IPv6 Static Routing

In this hands-on exercise, we configure IPv6 addresses on 3 routers in a triangle. Then we configure IPv6 static routes to allow the 6 IPv6 subnets (3 loopback, 3 P2P links) to be accessible on all 3 routers.

Static routes are easy to understand. At first glance they appear simple. You just manually configure which next-hop to go to for each subnet destination. But in actual use they are very complex. In our example with 3 routers and 6 subnets, we end up using 12 static route commands to implement our routing. Even then we do not achieve full redundancy, because static routes do not reroute around network failures. Even a small production network with approximately 20 routers would have too many static route commands necessary to make a static-route implementation feasible. In the real world, using dynamic routing protocols to minimize manual configurations (minimizing both effort and errors) is necessary to achieve a robust environment.

That said, static routes are sometimes useful at the edge of your network. You redistribute static routes into your routing protocol at the edge of your network where you don't want to dynamically route with routers outside your administrative control. The goal there is just to use the static route to inject a route into your routing protocol. Not to use the static route as your primary routing mechanism.