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###### 日期：2022-05-05 12:06

CS265 Computer Networking:

Instructions: Complete the following problem. There are 100 total points. If a problem has multiple parts,

they are equi-valued. Please use a word processor or text editor for solutions, and submit as a pdf file via

blackboard.

Problem 1 Imagine two autonomous systems ASX and ASY , and assume all of the following:

? ASY has been allocated a prefix PY containing a host H’s public IP address.

? A router R resides within the domain of ASX.

? ASX uses RIP for intra-AS routing, a shortest AS-PATH policy for inter-AS routing, and an intra-AS

hot-potato policy to break AS-PATH ties for inter-AS routing.

? ASX contain three gateways, G1, G2, and G3.

? R has three interfaces, I1, I2, and I3, and entries (G1, I1) and (G2, I2), in its forwardingtable.

? G1 is fewer hops away than G2 along their respective shortest paths from R, though the path to G1

traverses an older set of links with lower average throughput.

? At time Tj the only path to prefix PY to have been advertised to ASX is ASB ASC ASY with

Answer each of the following:

a. If G7 has an inter-AS peering link with ASX only to G2, to which interface will R forward datagrams

b. Imagine that at some time Tk, which is after Tj, a new BGP advertisement is received at ASX for

prefix PY , with AS-PATH ASD ASE ASY and NEXT-HOP G8. Furthermore, G8 has a peering

link with both G2 and G1. Should R’s forwarding table be updated based on this new information?

If so, how?

c. Suppose that instead of RIP, ASX uses OSPF with an average throughput metric for routing path

costs. Should R’s forwarding table be updated after receipt of the new advertisement at time Tk in

this case?

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