Route Tables and Route Table Entries

[This is preliminary documentation and subject to change.]

The RTM maintains distinct route tables for each protocol family. Currently explicit support is provided for the Internet protocol (IP) and Internet Packet Exchange (IPX) routing protocol families. Regardless of the protocol family, each route entry contains the following information.

• Destination network.
• Identifier of the protocol that added the route.
• Index of interface through which the route was obtained.
• Address of the next hop router. RRAS will use this router to forward packets to the destination network if the network is not directly connected.
• The time the route was created or last updated.
• The amount of time this route should be kept in the routing table. If this amount of time elapses, and the route has not been updated, the RTM will remove the route from the table (in this case, the route is said to have "aged out").
• Data specific to the protocol family. This data is transparent to RTM. However, if this data changes for a route that is designated as a "best route," the RTM will send out route-change notification.
• Data specific to the routing protocol. This data is completely transparent to the RTM in that changes to this data will not cause route change notification.

The following values taken together uniquely identify a route in the routing table.

• Destination network.
• Protocol identifier.
• Interface Index.
• Address of next-hop router.

In general, the RTM creates separate entries for routes that differ in any of these parameters values. However, an exception is made for routing protocols that do not keep more that one entry for each destination network. For these protocols, the RTM ignores differences in interface index or next-hop address. An example of such a protocol would be the RRAS implementation of Open Shortest Path First (OSPF).