Cisco Systems 78-11741-02 manual Suppressing Forward and Reverse Record Options, IPC-26

Configuring IP Addressing

Configuring Address Resolution Methods

Suppressing Forward and Reverse Record Options

To dynamically detect link layer filtering in NBMA networks (for example, SMDS address screens), and to provide loop detection and diagnostic capabilities, NHRP incorporates a Route Record in request and reply packets. The Route Record options contain the network (and link layer) addresses of all intermediate Next Hop Servers between source and destination (in the forward direction) and between destination and source (in the reverse direction).

By default, Forward Record options and Reverse Record options are included in NHRP request and reply packets. To suppress the use of these options, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)# no ip nhrp record	Suppresses Forward and Reverse Record options.

Specifying the NHRP Responder Address

If an NHRP requester wants to know which Next Hop Server generates an NHRP reply packet, it can request that information by including the responder address option in its NHRP request packet. The Next Hop Server that generates the NHRP reply packet then complies by inserting its own IP address in the NHRP reply. The Next Hop Server uses the primary IP address of the specified interface.

To specify which interface the Next Hop Server uses for the NHRP responder IP address, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)# ip nhrp responder type number	Specifies which interface the Next Hop Server uses to determine
	the NHRP responder address.

If an NHRP reply packet being forwarded by a Next Hop Server contains the IP address of that server, the Next Hop Server generates an error indication of type “NHRP Loop Detected” and discards the reply.

Changing the Time Period NBMA Addresses Are Advertised as Valid

You can change the length of time that NBMA addresses are advertised as valid in positive NHRP responses. In this context, advertised means how long the Cisco IOS software tells other routers to keep the addresses it is providing in NHRP responses. The default length of time is 7200 seconds (2 hours). To change the length of time, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)# ip nhrp holdtime seconds	Specifies the number of seconds that NBMA addresses are
	advertised as valid in positive NHRP responses.

Cisco IOS IP Configuration Guide

IPC-26