Information Technology Reference
In-Depth Information
Metric:
Indicates how many router hops to reach the destination. The metric is be-
tween 1 and 15 for a valid route or 16 for an unreachable or infinite route.
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Again, as in RIPv1, the router permits up to 25 occurrences of the last five 32-bit words
(20 bytes) for up to 25 routes per RIP message. If the AFI specifies an authenticated mes-
sage, the router can specify only 24 routing table entries. The updates are sent to the mul-
ticast address of 224.0.0.9.
RIPv2 Timers
RIPv2 timers are the same as in RIPv1. They send periodic updates every 30 seconds.
The default invalid timer is 180 seconds, the hold-down timer is 180 seconds, and the
flush timer is 240 seconds. Yo u can write this list as 30/180/180/240, representing the
U/I/H/F timers.
RIPv2 Design
Things to remember in designing a network with RIPv2 include that it supports VLSM
within networks and allows for the summarization of routes in a hierarchical network.
RIPv2 is still limited to 16 hops; therefore, the network diameter cannot exceed this limit.
RIPv2 multicasts its routing table every 30 seconds to the multicast IP address 224.0.0.9.
RIPv2 is usually limited to accessing networks where it can interoperate with servers run-
ning
routed
or with non-Cisco routers. RIPv2 also appears at the edge of larger internet-
works. RIPv2 further provides for route authentication.
As shown in Figure 10-9, when you use RIPv2, all segments can have different subnet masks.
Router A
Router B
172.16.3.4/30
172.16.2.64.0/26
172.16.1.0/24
Figure 10-9
RIPv2 Design
RIPv2 Summary
The characteristics of RIPv2 follow:
Distance-vector protocol.
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Key
To p i c
Uses UDP port 520.
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Classless protocol (support for CIDR).
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Supports VLSMs.
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Metric is router hop count.
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Low scalability: maximum hop count is 15; infinite (unreachable) routes
metric of 16.
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