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CS 458 –Internet Engineering
Spring 2004
Second Exam
Instructions (read carefully):
- This is a closed book and closed notes in-class exam.
- If any problem is unclear, or you believe some assumptions need to be made, state your assumptions at the beginning of your solution.
- Keep your answers short.
- Explain all steps of your solutions.
- Make sure your answers are legible. If we cannot read an answer, we will not grade it.
- The exam must be pledged.
1 20 2 15 3 10 4 15 5 10 Total 70
Name:
Email:
Pledge:
Problem 1. (20 Points ) Networks with bridges and routers.
Figure 1 (next page) shows a network of bridges (LAN switches), routers and hosts. The IP configuration of the hosts and routers is as follows: Ethernet Interface eth0 Ethernet Interface^ eth^
Default Gateway
Host1 10.0.3.21/24 -- 10.0.3.
Host2 10.0.3.12/16 -- 10.0.1.
Host3 10.0.1.11/24 -- 10.0.1.
Host4 10.0.4.41/16 -- 10.0.4.
Router1 10.0.3.3/24 10.0.1.2/24 10.0.3.
Router2 10.0.3.2/24 10.0.4.3/24 10.0.3.
Assume that Proxy ARP is enabled on all interfaces on all routers.
a. (10 points) Describe the route taken by the Echo Request and Echo Reply messages of the following PING commands. For each PING command, state if it is successful. If not, state where the command fails.
- On Host 2: ping 10.0.3.
- On Host 4: ping 10.0.1.
b. (5 points) Suppose that Proxy ARP was disabled on all routers. Explain how the outcomes in (a) be different.
c. (5 points ) Is it necessary to run the Spanning Tree Protocol (STP) on Bridges1 and 2? Explain your answer.
Problem 2. (15 points) DHCP
In Figure 2, Host1 is a DHCP client, Host 2 is a DHCP server. Router 1 is an IP router (i.e., IP forwarding is enabled), that is also configured as DHCP relay server.
a) (5 Points) Explain why Router1 needs to be configured as a DHCP relay server.
b) (5 Points) Describe how the relay server processes and directs a DHCP Request from Host 1 and the DHCP Reply to Host 1. Does the DHCP relay server modify the IP headers of the DHCP packets?
c) (5 Points) List the IP source and destination addresses in the DHCP Request and the DHCP Response. If the addresses are changed at Router1, show the original and the modified addresses.
Problem 3. (10 Points ) NAT and DHCP Most low-cost broadband (Cable/DSL) IP routers for home use perform the following functions: ß DHCP client ß DHCP server ß IP masquerading
Explain how these functions are used to provide Internet access to multiple computers on a home network.
Problem 4. (15 Points) DNS Figure 3 depicts the DNS resolver of host neon.cs.virginia.edu and the name server of the host. The figure also shows a DNS root server and the name servers for zones “.com” and “cisco.com”.
a) (10 Points) Show the sequence of DNS queries and replies when the resolver makes a query for the IP address of “www.cisco.com”. Indicate the content of the queries and the replies. Assume that the resolver issues a recursive query.
b) (5 Points) How does the sequence of queries and replies differ when the resolver sends an iterative query?
Figure 3.
Problem 5. (10 Points) IP Multicast
a) (5 Points) Explain the flood-and-prune method for building multicast rout ing trees.
b) (5 Points) Why is flood-and-prune not a good approach when the number of receivers in the multicast group is small?
