Abstract; Introduction To Ripv2; Rip Timers And Stability Features - Motorola PMP320 Configuration Manuallines

4 Abstract

Primary purpose of this document is to cover Layer3 functionality of PMP320 and how to
integrate PMP320 into an existing customer network. We start with the Introduction of
RIPv2 routing protocol, then we move on to compare some popular routing protocols with
RIPv2. Our next section provides sample customer network setups and "redistribution"
configuration examples in relation to integrating PMP320 with RIPv2.Routing protocols
covered include RIPv2, OSPF, EIGRP and BGP on Cisco Routers (6500 and 7200 series).
5

Introduction to RIPv2

RIP process operates from UDP port 520, all RIP messages are encapsulated in a UDP
datagram with both the source and destination port fields set to 520. RIP defines two
messages types: Request and Response messages. A Request message is used to ask
neighboring routers to send an update. A Response message carries the update. The metric
used by RIP is "hop count", with 1 signifying a directly connected network of the
advertising router and 16 signifying as unreachable network.
RIPv2 uses multicast updates to other RIPv2 speaking routers, using the reserved class D
address 224.0.0.9. The advantage of multicasting is that devices on the local network that
are not connected with RIP routing do not have to spend time "unwrapping" broadcast
packets from the router.

5.1 RIP Timers and Stability Features

After the RIP process is enabled, the router sends a Response message out every RIP
enabled interface every 30 seconds. The Response message (update) contains the routers
"full" route table with the exception of entries suppressed by the split horizon rule.
RIP process employs several timers, they are as follows:
Update Timer: RIP routers send periodic updates every 30 seconds to directly connected
neighbors. These updates contain the entire route table. The update timer initiating this
periodic update includes a random variable to prevent table synchronization. As a result,
the time between individual updates from a typical RIP process might be from 25 to 35
seconds.
Expiration Timer: The expiration timer is initialized to 180 seconds, whenever a new
route is established. If an update for a route is not heard within that 180 seconds
(equivalent to six update periods), the hop count for the route is changed to 16, marking
the router as unreachable. Cisco IOS refers this timer as "invalid" timer.
Flush timer: It is set to 300 seconds (120 seconds longer then the expiration timer or 10
times the Update timer). During this period the route will be advertised with the
unreachable metric (hop count is set to 16) until the Flush timer expires, at which time the
route will be removed from the route table.