Enhanced IGRP and Passive Interface

If you do not want to enable Enhanced IGRP on an interface, you must set it in passive mode. This prevents Enhanced IGRP from sending multicast hellos to an interface. The question then becomes: When would you want to set a passive interface?

There are situations in which you should set Enhanced IGRP in passive mode. First, you would use the passive mode when a router is connected to a large number of customer sites and you do not want to run Enhanced IGRP on those links. If you are an Internet Service Provider (ISP), your external peering router interface is the next hop for EBGP routes, and it must be advertised into your IGP. In this case, simply make the interface passive so that you do not send Enhanced IGRP hellos to an external neighbor.

This way, you will continue to advertise the interface into your IGP for the next hop of an EBGP route, and you will not form an Enhanced IGRP neighbor relationship. When an interface is passive for Enhanced IGRP, nothing is sent from it from a protocol standpoint.

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