Cover by Gary A. Donahue

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Configuring the Routers

We’ve done all of our discovery and planning. Now it’s time to get to the meat of the exercise: configuring the routers. For this implementation, we’re going to configure QoS on the edge routers that connect the T1 to the individual buildings. We will do marking, classification, and policing on the same device, but remember that these steps can be separated onto discrete devices as needed. VoIP phones will usually mark their packets, so we’ll assume that they’re doing so on our network.

To configure LLQ, we need to configure three things: class maps, policy maps, and service policies.

Class Maps

We need to identify which packets should be marked. To do this, we will create class maps, which will match specific types of traffic. There are a wide variety of matching possibilities for class maps—they can match specific IP precedence values, DSCP values, or even ACLs. The only function class maps accomplish is matching.

The following class map, called Voice-Calls, matches either DSCP EF (express forwarding) or IP precedence 5:

class-map match-any Voice-Calls
  description [---[ Actual Calls (Set on IP Phones and Dial-Peers) ]---]
  match ip dscp ef
  match ip precedence 5

This is technically unnecessary, however, because (as discussed in Chapter 31) the two are synonymous. Let’s change it so it’s easier to read:

class-map match-any Voice-Calls
  description [---[ Actual Calls (Set on IP Phones and Dial-Peers) ]---]
  match ip precedence 5

We could just as easily have used DSCP ...

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