E1. Describe how loops can be detected in BGP. E2. Consider a router that interc

Question

E1. Describe how loops can be detected in BGP.

E2. Consider a router that interconnects three subnets: subnet 1, subnet 2 and subnet 3. Assume all the interfaces in each of these subnets are required to have an IP address that starts with 223.1.17/24. If subnet 1, subnet 2 and subnet 3 are required to support at least 60, 90 and 12 interfaces respectively, provide three network addresses of the form a.b.c.d/x that satisfy the constraints.

E3. Consider sending a 2400 byte datagram into a link that has an MTU of 700 bytes. How many fragments are generated?

E4. Consider the same datagram and the same MTU as in E3. Suppose the original datagram is stamped with the identification number 422. For each of the fragments, what are the values of the ID, offset and flag?

E6. Give two reasons why there are different intra-AS and inter-AS routing.

E7. List the 3 broad classes of MAC protocols.

E8. List the concerns of token passing MAC protocol.

Explanation / Answer

E1) Answer: BGP has builtin loop detection via the AS_PATH attribute. The loop can be detected if an AS appears more than one times. E2) Answer 223.1.17/24 (Network ID) 11011111 00000001 00010001 ???????? Subnet 1 11011111 00000001 00010001 0??????? Subnet 2 11011111 00000001 00010001 10?????? Subnet 3 11011111 00000001 00010001 11?????? all 223.1.17/24 Subnet 1 223.1.17.0/25 Subnet 2 223.1.17.128/26 Subnet 3 223.1.17.192/26 E3) (240020)/680=4 max size of data field in fragment = 700 – 20 =680. All fragments’ identification number is 422. All fragments except the last one should be 700 bytes, the last datagram should be 360 bytes. The offset of 4 fragments should be 0, 85, 170, 255. The fragment bit flag of first 3 fragments will be 1, the last fragment bit flag will be 0. E6) policy: · Inter-As:admin wants control over how its traffic is rputed and who routes through it's net · Intra-As:single admin,so no policy decisions needed scale: · hierarchical routing saves table size,reduced update traffic performance: · Inter-As:can focus on performance · Intra-As:policy may dominate over performance E7) Three broad classes: channel partitioning divide channel into smaller"pieces"(time slots,frequency,code) allocate piece to node for exclusive use random access channel not devided,allow collisions recover from collisions taking turns nodes take turns,but nodes with more to send can take longer turns E8) concerns: · token overhead · latency · single point failure

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