Information Technology Reference
In-Depth Information
The following describes each field:
Command:
Indicates whether the packet is a request or response message. This field
is set to 1 for a request and to 2 for a response.
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Version:
Set to 1, the first version of RIPng.
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IPv6 prefix:
The destination 128-bit IPv6 prefix.
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Route Ta g :
As with RIPv2, this is a method that distinguishes internal routes
(learned by RIP) from external routes (learned by external protocols). Ta g ge d during
redistribution.
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Prefix Length:
Indicates the significant part of the prefix.
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Metric:
This 8-bit field contains the router hop metric.
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RIPv2 has a Next Hop field for each of its route entries. An RTE with a metric of 0xFF in-
dicates the next-hop address to reduce the number of route entries in RIPng. It groups all
RTEs after it to summarize all destinations to that particular next-hop address. Figure 10-
11 shows the format of the special RTE indicating the next-hop entry.
0 1 2 3
01234567890123456789012345678901
IPv6 next-hop address
128 bits
Must be zero
zeros
0xFF
Figure 10-11
RIPng Next-Hop Route Table Entry
RIPng Design
RIPng has low scalability. As with RIPv2, it is limited to 15 hops; therefore, the network
diameter cannot exceed this limit. RIPng also broadcasts its routing table every 30 sec-
onds, which causes network overhead. RIPng can be used only in small networks.
RIPng Summary
The characteristics of RIPng are as follows:
Distance-vector protocol for IPv6 networks only.
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Key
To p i c
Uses UDP port 521.
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Metric is router hop count.
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Maximum hop count is 15; infinite (unreachable) routes have a metric of 16.
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Periodic route updates are sent every 30 seconds to multicast address FF02::9.
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Uses IPv6 functions for authentication.
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Implements split horizon with poison reverse.
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Implements triggered updates.
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