Configuring Network Interfaces for RIP
For each interface that participates in the RIP routing process, yo u must sp ecify the
protocol message type accepted (i.e., RIP version) and the message type s ent (i.e.,
RIP version or compatibility mode), the method for preventing loopback of protocol
messages, and whether or not authentication is used (i.e., authenticati on only
applies if RIPv2 messages are being sent or received).
Command Usage
Specifying Receive and Send Protocol Types
• Setting the RIP Receive Version or Send Version for an interfac e overrides th e
global setting specified by the RIP / Gener al S ett ings , Gl obal RIP Vers ion f ield .
• You can specify the Receive Version based on these op tions:
- Use “RIPv1” or “RIPv2” if all routers in the l ocal net work are bas ed on RI Pv1 or
RIPv2, respectively.
- Use “RIPv1 or RIPv2” if some routers in the local network are using RIP v2, but
there are still some older routers using RIPv1.
- Use “Do Not Receive” if you do not want to add any dynamic entries to the
routing table for an interface. (For example, you may on ly want t o allow stat ic
routes for a specific interface.)
• You can specify the Send Version based on these options:
- Use “RIPv1” or “RIPv2” if all routers in the l ocal netwo rk a re based on RIPv 1 or
RIPv2, respectively.
- Use “RIPv1 Compatible” to propagate route information by broadcasting to other
routers on the network using the RIPv2 advertisement list, inste ad o f
multicasting as normally required by RIPv2. (Using this mode allows RIPv1
routers to receive these protocol messages, but still a llows RI Pv2 route rs to
receive the additional information provided by RIPv2, including subnet mask ,
next hop and authentication information.)
- Use “Do Not Send” to passively monitor route information advertised by other
routers attached to the network.
Loopback Prevention
Just as Layer 2 switches use the Spanning Tree Algorithm to prevent loops, routers
also use methods for preventing loops that would cause endless retransmission of
data traffic. When protocol packets are caught in a loop, links will be congested, and
protocol packets may be lost. However, the network will slowly converge to the new
state. RIP utilizes the following three methods that can provide faster co nvergence
when the network topology changes and prevent most loops from occur ring:
• Split Horizon – Never propagate routes back to an interface port from which they
have been acquired.
• Poison Reverse – Propagate routes back to an i nterface from which they ha ve
been acquired, but set the distance-vector metrics to infinity. (T hi s p rovides faster
convergence.)
• Triggered Updates – Whenever a route gets changed, broadcast an update
message after waiting for a short random delay, but without waiting for the periodic
cycle.

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Unicast Routing

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