Consider the following network Suppose AS3 and AS2 arc runni

Consider the following network. Suppose AS3 and AS2 arc running OSPF for their intra-AS routing protocol. Suppose ASI and AS4 arc running RIP for their intra-AS routing protocol. Suppose cBGP and iBGP are used for the inter-AS routing protocol, Initially suppose there is no physical link between AS2 and AS4. a) Router 4b learns about x from which routing protocol? b) Router 1c learns about x from which routing protocol? c) Router 1d learns about x from which routing protocol? d) Router1d learns about prefix x it will put an entry (x, I) in its forwarding table. Will I be equal to I_1 or I_2 for this entry? Explain. e) Now suppose that there is a physical link between AS2 and AS4, shown by the dotted line. Suppose router 1d learns that x is accessible via AS2 as well as via AS3. Will I be equal to I_1 or I_2? Explain. f) Now suppose there is another AS, called AS5, which lies on the path between AS2 and AS4 (not shown in the figure above). Suppose router 1d learns that x is accessible via AS2-AS5-AS4 as well as via AS3-AS4. Will I be equal to I_1 or I_2? Explain.

Solution

Answer:a)RIP
b)eBGP
c)iBGP
d)L1 . This interface begins the least cost path from 1d towards the gateway router 1c.
e)L2.Both routes have equal AS-PATH length but L2 begins the path that has the closest NEXT-HOP router
f) L1.L1 begins the path that has the shortest AS-PATH.