1. CS 672 1 Summer 2003 Quiz 1 Q1) Answer the following: List one protocol that is commonly used for intra AS routing? List one protocol that is used for inter-AS routing? Q2) Answer the following: A singled-homed AS that does not carry transit traffic is known as? Look at Figure 1 and categorize the AS3 is transit or non-transit? Briefly explain the reason? Q3) Suppose the administrator configures a route for a destination P1 on the router R1 with R2 as the next hop. Suppose the link L1 between R1 and R2 goes down. What happens to the traffic from R1 to R3 destined for P1? Would L1 failure cause the route for P1 to disappear from R1’s routing table? Explain why or why not. Q4) Repeat the previous question with the assumption that the route for P1 is learned dynamically via IGP such as OSPF.

2. CS 672 2 Summer 2003 Quiz 1 Q5) Briefly list some of the key differences between OSPF and BGP? a) b) c) Q6) Briefly describe few benefits of classless interdomain routing (CIDR) a) b) Q7) Briefly answer the followings a) Is IP reachability (e.g., ability to ping) necessary for establishing a BGP session? Why? b) Look at Figure 3, suppose BGP session was successfully established. Now the link L1 fails. What happens to the BGP session? c) What mechanism does BGP use to detect BGP session failure?

3. CS 672 3 Summer 2003 Quiz 1 Q8) Briefly answer the following: a) How does BGP advertise or withdraw routes (i.e., what message)? b) Can BGP advertise multiple routes in one message? c) Can BGP withdraw multiple routes in one message? Q9) Briefly answer the following: a) Why BGP attributes are important ? b) Can one influence the traffic flow by manipulating BGP path attributes? Q10) Briefly answer the followings a) What Path attribute does BGP use to detect routing loops? b) Look at Figure 4, How AS 100 can cause the traffic flow along AS 500, AS 400, AS 300?

4. CS 672 4 Summer 2003 Figure 1 AS 1 destinations (P1,P2) destinations (P3,P4) AS 2 AS 3 destinations (P5,P6) BGP Update Msg (P1, P) (P3,P4,P5,P6) BGP Update Msg (P3,P4) BGP Update Msg (P1,P2, P5,P6)

5. CS 672 5 Summer 2003 Figure 2 R1 R3 R2 L1 P1

6. CS 672 6 Summer 2003 Figure 3 R1 R4 L1 Fails iBGP OSPF

7. CS 672 7 Summer 2003 Figure 4 Update (NLRI= 172.64.16.0/16, AS_Path{AS100,AS200}) AS 100 AS 200 AS 300 AS 500 DS3 OC3 ( 155 Mb/s) OC3 AS 400 OC3 172.64.16.0/16 Update (NLRI= 172.64.16.0/16, AS_Path{AS100,AS300, As400}}) Traffic flow