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| 4.1 |  | RIP v2 Overview |
| 4.1.4 |  | Compatibility with RIP v1 |

RIP v2 handles updates in a flexible manner. If the Version Number field indicates version 1 and if any bits in the Unused field are set to one, the update is discarded. If the RIP version is greater than one, then the fields defined as unused are ignored and the message is processed. Therefore, newer versions of the RIP protocol are backward compatible with previous RIP versions.

RFC 1723 defines a compatibility switch with four settings, which allows versions 1 and 2 to interoperate:

1. RIP v1, in which only RIP v1 messages are transmitted
2. RIP v1 Compatibility, which causes RIP v2 to broadcast its messages instead of multicast them so that RIP v1 may receive them
3. RIP v2, in which RIP v2 messages are multicast to destination address 224.0.0.9
4. None, in which no updates are sent

RFC 1723 recommends that switches be configurable on a per-interface basis. The Cisco commands for settings 1 through 3 are presented in the section Configuring RIP v2. The Cisco command for setting 4 is accomplished by using the

passive-interface command.

Additionally, RFC 1723 defines a receive control switch to regulate the reception of updates. The four recommended settings of this switch are listed in the following:

1. RIP v1 only
2. RIP v2 only
3. Both
4. None

This switch should also be configurable on a per interface basis. The Cisco commands for settings 1 through 3 are also presented in the configuration section of this module. Setting 4 can be accomplished by using an access list to filter UDP source port 520, by not including a network statement for the interface, or by configuring a route filter.

| Web Links RFC 1723 http://www.ietf.org/rfc/rfc1723.txt ?number=1723