Accepting RIP Packets with Nonzero Values in Reserved Fields

Some of the reserved fields in RIP version 1 packets must be zero, while in RIP version 2 packets most of these reserved fields can contain nonzero values. By default, RIP discards version 1 packets that have nonzero values in the reserved fields and version 2 packets that have nonzero values in the fields that must be zero. This default behavior implements the RIP version 1 and version 2 specifications.

If you find that you are receiving RIP version 1 packets with nonzero values in the reserved fields or RIP version 2 packets with nonzero values in the fields that must be zero, you can configure RIP to receive these packets in spite of the fact that they are being sent in violation of the specifications in RFC 1058 and RFC 2453. To receive packets whose reserved fields are nonzero, include the no-check-zero statement:

For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.