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1 via B
2 via C
3 via D
1 via C
2 via D
3 via B
1 via D
4 via B
1 via E
Distance vector protocols can operate in two different modes : `periodic updates` and `triggered updates`. `Periodic updates` is the default mode for a distance vector protocol. For example, each router could advertise its distance vector every thirty seconds. With the `triggered updates` a router sends its distance vector when its routing table changes (and periodically when there are no changes).
Consider a distance vector protocol using split horizon and `periodic updates`. Assume that the link `B-C` fails. `B` and `C` update their local routing table but they will only advertise it at the end of their period. Select one ordering for the `periodic updates` and every time a router sends its distance vector, indicate the vector sent to each neighbor and update the table above. How many periods are required to allow the network to converge to a stable state ?
Consider the same distance vector protocol, but now with `triggered updates`. When link `B-C` fails, assume that `B` updates its routing table immediately and sends its distance vector to `A` and `D`. Assume that both `A` and `D` process the received distance vector and that `A` sends its own distance vector, ... Indicate all the distance vectors that are exchanged and update the table above each time a distance vector is sent by a router (and received by other routers) until all routers have learned a new route to each destination. How many distance vector messages must be exchanged until the network converges to a stable state ?
Consider again the network shown above. After some time, link state routing converges and all routers compute the same routing tables as above.
An important difference between OSPF and RIP is that OSPF routers flood link state packets that allow the other routers to recompute their own routing tables while RIP routers exchange distance vectors. Consider that link `B-C` fails and that router `B` is the first to detect the failure. At this point, `B` cannot reach anymore `C`, `D` and `E`. `C` cannot reach `B` and `A` anymore.
Router `B` will flood its updated link state packet through the entire network and all routers will recompute their forwarding table. Upon reception of a link state packet, routers usually first flood the received link-state packet and then recompute their forwarding table. Assume that `B` is the first to recompute its forwarding table, followed by `D`, `A`, `C` and finally `E`.
After each update of a forwarding table, verify which pairs of routers are able to exchange packets. Provide your answer using a table similar to the one shown above.


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4 years ago
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4 years ago
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locale/pot/exercises/network.pot, string 68