10.1.4 Learning route information

<Structure of this section>

(1) Learner of route information

In RIP, routing information can be learned from all neighboring routers on the network specified by the network configuration command. This includes routers on a network to which the secondary address of the interface belongs.

(2) Timing of route information learning/switching

The following table describes the functionality related to the timing of route updates learned via RIP.

Table 10-8: Timing of route information learning and switching
Functionality	Description
Response packets received from neighboring routers	Adds, changes, or deletes routing information as reported by neighboring routers.
Aging timeout	Deletes routing information if there is no periodic notification from a neighboring router for a set time.
Recognizing interface failures	Deletes routing information learned from a RIP-enabled interface on which a failure has been discovered.

(a) Receiving a response packet

Under RIP, the routing information in the response packets received from neighboring routers is written to the Switch's routing table. The following figure shows the generation of routing information from a received response packet.

Figure 10-8: Generating route information by receiving a response packet

(b) Aging timeout

Routing information generated from a received response packet is monitored by an aging timer. The aging timer is reset (cleared) by a periodic advertisement from the neighboring router. If the router fails to generate an advertisement for the route being monitored for 180 seconds (aging timeout value) due to a hardware failure or a line error between the router and switch, the affected entries are deleted from the switch's routing table. The following figure shows deletion of routing information by aging timeout.

Figure 10-9: Deleting route information due to an aging timeout

(c) Recognizing Interface Failures

On recognizing that the interface that connects the switch to a neighboring router has failed, the Switch immediately deletes all routing information learned from that interface. The following figure shows the deletion of routing information due to an interface failure.

Figure 10-10: Deleting routing information due to an interface failure