24-port NWay Ethernet Switch User’s Guide
Switch Management and Operating Concepts
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means the RIP 1 cannot be used to propagate variable-length
subnet addresses or classless addresses.
Note:
RIP 1 can only be used with classful or fixed-length
subnet addresses.
If a router running RIP 1 connects to one or more networks that
are subnets of a prefix N as well as to one or more networks that
are not part of N, the router must prepare different update
messages for the two types of interfaces. Updates sent over the
interfaces that are subnets of N can include subnet routes, but
updates sent over other interfaces cannot. Instead, when
sending over other interfaces the router is required to aggregate
the subnet information and advertise a single route to network N.
RIP Version 2 Extensions
The restriction on address interpretation means that version 1 of
RIP cannot be used to propagate either variable length subnet
addresses or the classless addresses used with CIDR. When
version 2 of RIP (
RIP2
) was defined, the protocol was extended
to include an explicit subnet mask along with each address. In
addition, RIP2 updates include explicit next-hop information,
which prevents routing loops and slow convergence. As a result,
RIP2 offers significantly increased functionality as well as
improved resistance to errors.
RIP2 Message Format
The message format used with RIP2 is an extension of the RIP1
format, with additional information occupying unused octets of
the address field. In particular, each address includes an
explicit next hop as well as an explicit subnet mask.
