b. (8 marks) Consider the routing scenario in the Figure shown below. An autonomous system (AS1) is connected to the Internet via two connections. The router R1 in Sydney is running EBGP with one provider over a Tl circuit, and the router R2 in Melbourne is running EBGP with another provider over a T3 circuit Inside AS1, the two border routers R1 and R2 are running IBGP and EBGP, but are not physically connected. All communication between R1 and R2 go via internal routers R3, R4 and R5. The internal routers R3, R4, and R5 are non-BGP routers and exchange routes via an IGP with all other routers in the AS. In the current scenario, R1 and R2 are both receiving full routes from their parent providers. These routers are also injecting a 0/0 default route inside AS1. Assume also that AS1 runs the primary/backup technique to enable the MEL T3 link to be the primary. The SYD link will be used as a backup, and therefore all outbound traffic that reaches R1 will now need to be directed back towards R2. Interior routers R3, R4, and R5 do not see any of the exterior routes and follow defaults towards R1 and R2 according to the IGP metric. Identify and describe one specific routing problem that is likely to occur in this scenario. Recommend some alternate ways to avoid this problem. (300 words). AS1 R4 R3 R5 R1 R2 b. (8 marks) Consider the routing scenario in the Figure shown below. An autonomous system (AS1) is connected to the Internet via two connections. The router R1 in Sydney is running EBGP with one provider over a Tl circuit, and the router R2 in Melbourne is running EBGP with another provider over a T3 circuit Inside AS1, the two border routers R1 and R2 are running IBGP and EBGP, but are not physically connected. All communication between R1 and R2 go via internal routers R3, R4 and R5. The internal routers R3, R4, and R5 are non-BGP routers and exchange routes via an IGP with all other routers in the AS. In the current scenario, R1 and R2 are both receiving full routes from their parent providers. These routers are also injecting a 0/0 default route inside AS1. Assume also that AS1 runs the primary/backup technique to enable the MEL T3 link to be the primary. The SYD link will be used as a backup, and therefore all outbound traffic that reaches R1 will now need to be directed back towards R2. Interior routers R3, R4, and R5 do not see any of the exterior routes and follow defaults towards R1 and R2 according to the IGP metric. Identify and describe one specific routing problem that is likely to occur in this scenario. Recommend some alternate ways to avoid this problem. (300 words). AS1 R4 R3 R5 R1 R2
