Microsoft ES4625, ES4649 manual Specifying Receive and Send Protocol Types, Loopback Prevention

3 Configuring the Switch

Configuring Network Interfaces for RIP

For each interface that participates in the RIP routing process, you must specify the protocol message type accepted (i.e., RIP version) and the message type sent (i.e., RIP version or compatibility mode), the method for preventing loopback of protocol messages, and whether or not authentication is used (i.e., authentication 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 interface overrides the global setting specified by the RIP / General Settings, Global RIP Version field.

•You can specify the Receive Version based on these options:

-Use “RIPv1” or “RIPv2” if all routers in the local network are based on RIPv1 or RIPv2, respectively.

-Use “RIPv1 or RIPv2” if some routers in the local network are using RIPv2, 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 only want to allow static routes for a specific interface.)

•You can specify the Send Version based on these options:

-Use “RIPv1” or “RIPv2” if all routers in the local network are based on RIPv1 or RIPv2, respectively.

-Use “RIPv1 Compatible” to propagate route information by broadcasting to other routers on the network using the RIPv2 advertisement list, instead of multicasting as normally required by RIPv2. (Using this mode allows RIPv1 routers to receive these protocol messages, but still allows RIPv2 routers 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 convergence when the network topology changes and prevent most loops from occurring:

•Split Horizon – Never propagate routes back to an interface port from which they have been acquired.

•Poison Reverse – Propagate routes back to an interface port from which they have been acquired, but set the distance-vector metrics to infinity. (This provides 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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