Step 3. Link Breakage and Routing Table Updates¶

Goals¶

We demonstrate how RIP updates the routing tables after changes occur in a network topology.

Network Configuration¶

We keep the network configuration same as the previous step, except that we will schedule a break with the help of ScenarioManager. RIP should update the routing information in the routing tables of routers to eliminate the references to the broken link. Here, for the reliable convergence of routing tables, we need to enable SplitHorizon though (we will postpone discussion of this issue until Step 6 of the tutorial).

The configuration in omnetpp.ini is the following:

[Config Step3]
description = "Link breakage"
extends = Step2

# Enable split horizon in order for the scenario to work properly
*.router*.rip.ripConfig = xml("<config> \
                                  <interface hosts='router*' mode='SplitHorizon' /> \
                               </config>")
# Disable ping application
*.host0.numApps = 0

*.scenarioManager.script = xml("<scenario> \
                                    <disconnect t='50' src-module='router2' dest-module='switch2' /> \
                                </scenario>")

The last key in the above figure is for scheduling a break.

Experiment¶

In the video below observe that at t=50 seconds, as directed by the scenario manager script, the link connecting router2 and switch2 breaks (note that the video starts approximately at t=30, after the routing tables stabilize).

TODO explain why arrow from host6 remains: It is a static route. RIP only controls routes between routers, and host routes are statically configured by Ipv4NetworkConfigurator.

Sources: omnetpp.ini, RipNetworkA.ned