CSIT340 HW05

HW 5 1. True or false: When an OSPF router sends its link state information, it sends only to its direct neighbors. Explain. ● False. It sends the link state information to all all routers in the entire AS. 2. True or false: When a RIP router sends its distance vector, it sends only to its direct neighbors. Explain. ● True. Every node sends its routes to its neighbors. Route information gradually spreads through the network. 3. Consider the following network. With the indicated link costs, use Dijkstra’s shortest-path algorithm to compute the shortest path from y to all network nodes. Show how the algorithm works by computing a table similar to Table 5.1 (in the 7 th edition of the textbook; if you are using the 6 th edition, that is Table 4.3). Step N’ D(t), p(t) D(u), p(u) D(v), p(v) D(w), p(w) D(y), p(y) D(z), p(z) 0 x ∞ ∞ 3,v 6,w 6,y 8,z 1 xv 7,t 6,u 3,v 6,w 6,y 8,z 2 xvu 7,t 6,u 3,v 6,w 6,y 8,z 3 xvuw 7,t 6,u 3,v 6,w 6,y 8,z 4 xvuwy 7,t 6,u 3,v 6,w 6,y 8,z 5 xvuwyt 7,t 6,u 3,v 6,w 6,y 8,z 6 xvuwyz 7,t 6,u 3,v 6,w 6,y 8,z 4. Consider the network shown below, and assume that each node initially knows the costs to each of its neighbors. Consider the distance-vector algorithm.

HW 5 a. What are the distances from y to all other nodes after y receives one message from each of its direct neighbors (assuming that these messages are the only messages that have been sent and received so far in the entire system)? ● u -> y = 2 steps ● v -> y = 3 steps ● x -> y = 3 steps ● z -> y = 5 steps b. What are the distances from x to all other nodes after x receives one message from each of its neighbors? ● u -> x = 4 steps ● v -> x = 3 steps ● y -> x = 3 steps ● z -> x = 2 steps 5. Consider the network shown below. Suppose AS3 and AS2 are running RIP for their intra-AS routing protocol. Suppose AS1 and AS4 are running OSPF for their intra-AS routing protocol. Suppose eBGP and iBGP are used for the inter-AS routing protocol. Initially suppose there is no physical link between AS2 and AS4. a. Router 4c learns about prefix x from which routing protocol: OSPF, RIP, eBGP, or iBGP? ● OSPF b. Router 3b learns about x from which routing protocol? ● iBGP. Router 3a is not connected directly to AS4, only AS3. eBPG is used by 3c. The remaining all the router is AS3 will use IBGP with AS4 to connect.