A. The next questions are based on the figure of the network below connecting AS1, AS2, AS3, AS4 and AS5. End host X connects to Ethernet switch B (e.g. in the wiring closet of a building which in turn connect to the routers inside AS1 (e.g. campus backbone routers), which in turn connects to the public Internet provider AS2 via BGP router B1.
B. If Ethernet switches A-F run the Spanning Tree Protocol (remember all links have the same cost), and A is the root of the spanning tree, which of the following statements are true?
1. Packets from X to Y will travel along the path BAD. BCD is not part of the spanning tree rooted at A, and so packets will flow via A.
2. Packets from AD will travel indefinitely around the loop ADEFA, unless the TTL expires.
3. If switch A fails, X will no longer be able to communicate with Y.
4. All of the links between the switches will be used to forward regular data packets.
5. A-F will learn link state information from routers R1R6 and optimize the spanning tree between the switches accordingly.
C. AS1 uses OSPF to route packets internally using the link weights shown. BGP router B1 also takes part in the OSPF routing algorithm for AS1.
D. Assume the link from R4R3 fails, what is the shortest path now from R4 to B1?
E. If AS1 uses default routing, do routers R1-R6 contain separate routing entries for prefixes in AS4 and AS5?
F. Can B7 aggregate prefixes for AS5 before advertising them to AS3 and AS2?
G. Which of the following route advertisements does AS2 receive for prefixes in AS5?
1. 18.104.22.168/16 AS3 AS4
2. 22.214.171.124/16 AS4 AS5
3. 126.96.36.199/16 AS3 AS4 AS5
4. 188.8.131.52/16 AS5
5. 184.108.40.206/16 AS4 AS5
6. 220.127.116.11/16 AS3 AS4 AS5
H. If AS5 uses the Routing Internet Protocol (RIP) to route packets between routers R7 – R11 and B8, how many steps will Bellman Ford algorithm need to run in order to be sure the algorithm will converge?
I. Which of the following statements are true for the network as a whole?
1. Packets from X to Y are guaranteed to take the same path as packets from Y to X.
2. IP datagrams from X to Y will be transmitted with destination IP address of R4 and encapsulated in an Ethernet frame with destination Ethernet address of B.
3. IP datagrams from X to Y will be transmitted with destination IP address of Y and encapsulated in an Ethernet frame with destination Ethernet address of R4.
4. If an IP datagram with destination address 18.104.22.168 arrives to E, and is encapsulated in an Ethernet frame with destination address of R4, then the switches and routers will attempt to forward the packet via several hops to AS5.
J. A CSMA/CD network operates at 100Mb/s. The maximum distance between any pair of end hosts is 10km. What is the minimum size packet a host should send in order to detect collisions before it finishes transmitting the packet? Assume a propagation speed of 2 x 10^8m/s.
1. 100 bits.
2. 10,000 bits
3. 53 bytes
4. 2,000 bits