3Com 4007, Implementation Manual, Page: 382 / 684

382 C
HAPTER
16: IP R
OUTING
Compatibility Mode The RIP-1 compatibility mode determines how the software sends
periodic RIP-2 updates. (RIP-1 always uses the advertisement list when
sending RIP-1 advertisements.)
■
When the module is configured to advertise RIP-2 packets and
compatibility mode is
disabled
, the software uses the multicast
address of 224.0.0.9 when sending periodic updates. Doing so
reduces the load on hosts that are not configured to listen to RIP-2
messages.
■
When the module is configured to advertise RIP-2 packets and
compatibility mode is
enabled
, the software uses the advertisement
list for RIP-2 updates.
Cost You can use RIP to calculate the route metrics (the cost) for you. The cost
is the number of hops that the packet needs to get to its destination. The
RIP cost is a number between 1 and 15. (A number higher than 15 is not
allowed, because RIP cannot negotiate more than 15 hops.)
Most facilities assign a cost of 1 to all interfaces. However, if you have
two links with differing speeds, such as a dial-up link versus a direct link,
you may want to raise the cost of the dial-up link so that the direct link is
more likely to be used.
Poison Reverse Poison Reverse is a RIP feature that you use specifically with a scheme
called
Split Horizon . The module enables Poison Reverse by default.
Split Horizon avoids the problems that reverse-route updates can cause.
Reverse-route updates are sent to a neighboring router and include the
routes that are learned from that router. Split Horizon omits the routes
that are learned from one neighbor in the updates that are sent to that
neighbor (the reverse routes).