Cisco Systems 78-11741-02 manual IPC-24

Configuring IP Addressing

Configuring Address Resolution Methods

NHRP Configuration Task List

To configure the NHRP triggering and teardown of SVCs based on traffic rate, perform the tasks described in the following sections. The tasks in the first section are required, the tasks in the remaining section are optional.

•Changing the Rate for Triggering SVCs (Required)

•Applying the Rates to Specific Destinations (Optional)

Changing the Rate for Triggering SVCs

When NHRP runs with BGP over ATM media, there is an additional way to control the triggering of NHRP packets. This method consists of SVCs being initiated based on the input traffic rate to a given BGP next hop.

When BGP discovers a BGP next hop and enters this BGP route into the routing table, an NHRP request is sent to the BGP next hop. When an NHRP reply is received, a subsequent route is put in the NHRP cache that directly corresponds to the BGP next hop.

A new NHRP request is sent to the same BGP next hop to repopulate the NHRP cache. When an NHRP cache entry is generated, a subsequent ATM map statement to the same BGP next hop is also created.

Aggregate traffic to each BGP next hop is measured and monitored. Once the aggregate traffic has met or exceeded the configured trigger rate, NHRP creates an ATM SVC and sends traffic directly to that destination router. The router tears down the SVC to the specified destination(s) when the aggregate traffic rate falls to or below the configured teardown rate.

By default, NHRP will set up an SVC for a destination when aggregate traffic for that destination is more than 1 kbps over a running average of 30 seconds. Similarly, NHRP will tear down the SVC when the traffic for that destination drops to 0 kbps over a running average of 30 seconds. There are several ways to change the rate at which SVC set or teardown occurs. You can change the number of kbps thresholds, or the load interval, or both.

To change the number of kbps at which NHRP sets up or tears down the SVC to this destination, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip nhrp trigger-svc trigger-threshold	Changes the point at which NHRP sets up or tears
teardown-threshold	down SVCs.

You can change the sampling time period; that is, you can change the length of time over which the average trigger rate or teardown rate is calculated. By default, the period is 30 seconds; the range is from 30 to 300 seconds in 30-second increments. This period is for calculations of aggregate traffic rate internal to Cisco IOS software only, and it represents a worst case time period for taking action. In some cases, the software will act sooner, depending on the ramp-up and fall-off rate of the traffic.

To change the sampling time period during which threshold rates are averaged, use the following command in global configuration mode:

Command	Purpose
Router(config)# ip cef traffic-statistics [load-interval	Changes the length of time in a sampling period
seconds]	during which trigger and teardown thresholds are
	averaged.

Cisco IOS IP Configuration Guide

IPC-24