Q6. (10 Points) Consider the network shown below. Suppose AS3 and AS2 are running OSPF for their intra-AS routing protocol. Suppose AS1 and AS4 are running RIP 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.
4b
4c
4a
X
3c
3a
3b
AS4
2c
1c
2a
X
2b
1b
AS3
1a
X
AS2
1d
$l_1$
$l_2$
AS1
a) (4 Points) From which routing protocol (OSPF, RIP, eBGP, iBGP) each of the routers in the below table learns about prefix/subnet x?
Router Protocol
3c
3a
1c
1d
b) (6 Points) Once router d1 learns about x it will put an entry (x, I) in its forwarding table.
1. Will I be equal to $l_1$ or $l_2$ for this entry? Explain why in one sentence.
2. Now suppose that there is a physical link between AS2 and AS4, shown by the dotted line. Suppose router d1 learns that x is accessible via AS2 as well as via AS3. Will I be set to $l_1$ or $l_2$ for this entry? Explain why in one sentence.
3. Now suppose there is another AS, called AS5, which lies on the path between AS2 and AS4 (not shown in diagram). Suppose router d1 learns that x is accessible via AS2 AS5 AS4 as well as via AS3 AS4. Will I be set to $l_1$ or $l_2$ for this entry? Explain why in one sentence.