Junos® OS For Dummies®, 2nd Edition

Chapter 14

Working with Router Policies

In This Chapter

• Applying and validating routing policies
• Filtering your routes
• Aggregating routes

As discussed in Chapter 10, a router gathers location information from routing protocols and stores it in routing tables. These routing tables are then whittled down to include only the best information, and that information is used in the forwarding table, which is ultimately responsible for where traffic is forwarded hop-by-hop through the network.

This assumes, of course, that all the information a router sends and receives is correct. The information learned by the routing protocols could be wrong. You're receiving information from your neighbors, but if your neighbors are doing something you do not want them to do (like sending you traffic that should go somewhere else), you need a way of controlling how information is imported into your router. And on the flip side of the coin, you need a way to prevent your router from doing things that neighboring routers might not like (like sending them a lot of traffic they can't use). Routing policies are the solution to monitoring, filtering, or even modifying what gets into and what comes out of your routing and forwarding tables.

This chapter starts by creating and validating the policies that tell the router what to do with receive routing information, how to use it, and how to pass it on. Then we'll see how you can filter the routes themselves (really, the route's attributes) so that some ...