TMS zl Management and Configuration Guide ST.1.1.100430

9-16
Routing
RIP
■ A different neighbor advertises a route with a lower metric. The module
changes the route to list this neighbor as the next-hop address and enters
the new metric.
■ The module does not receive information about the route for the entire
length of the invalid interval. The module marks the route for deletion.
RIP Updates, v1 and v2
RIP update packets contain different information, depending on whether the
RIP version is 1 or 2.
An RIPv1 packet includes:
■ A command field—indicating whether the packet is a request or a reply
■ A version field (set at 1)
■ An address family field—set at 2, indicating that addresses are in IPv4
format
■ Up to 25 entries, each consisting of:
• A destination IP address
• A metric, which is the number of hops to the destination address from
the router that is sending the packet
When the module discovers a new or better route from a RIPv1 update, it
assumes that the neighbor from which it received the update is the next hop
for the route. The module adds one to the metric for its own routing table entry.
RIPv2 fixes several shortcomings of RIPv1. RIPv2 provides route summariza-
tion for classful networks and supports EGPs. A RIPv2 packet includes:
■ A command field—indicating whether the packet is a request or a reply
■ A version field
■ A routing domain—identifying the routing daemon that produced the
message, allowing a device to run several RIP processes at once
■ An address family field
■ A route tag (which includes the AS number for use with EGPs)
■ Up to 25 entries, each consisting of a:
• Destination IP address
• Subnet mask—providing support for variable-length subnets
• Next-hop IP address
• Metric—the number of hops to the destination address from the next-
hop address