Lab 4 Domain Name System - DNS CMPE 150

Transcription

1 Lab 4 Domain Name System - DNS CMPE 150 Lab Report Reports must be written and submitted individually as PDFs. Submission Instructions: Submit your report on the ecommons by 11:55 PM on the day of your registered lab section. Your submission should include an archive (tar or zip) containing your lab report and any other required files. Late/improper submissions will have a 10% grading penalty per day. Late labs will not be accepted after 3 days. Pre-Lab (20 points) Review the Linux man pages for hosts and ifconfig. 1. Describe the following terms that are used in the Domain Name System. a. Top-level domain. b. CNAME (canonical name) c. Resolver d. Name server e. Inverse lookup 2. Explain the following types of DNS queries: a. Iterative queries b. Recursive queries 3. What is the difference between a DNS domain and a DNS zone? 4. What are some of the top-level domains in the DNS namespace? 5. Are domain names case sensitive? What, if any, is the constraint on the length of domain names? 6. Provide a list of the names and IP addresses of all root servers of the Internet. 7. What is the purpose of the top-level domain arpa? In this lab, we will examine how DNS works by setting up name servers and observing traffic. This lab requires significantly more setup than previous labs, so please come prepared.

2 Part A Topology Setup We will be using the topology above for this lab. Wire the entities accordingly and configure the interfaces of the routers and PCs with the correct IP addresses. 1. Configure the interfaces on PCs using the following: For PC1: ifconfig eth /24 For PC2: ifconfig eth /24 For PC3: ifconfig eth /24 For PC4: ifconfig eth /24 2. Configure Router 1: i. Connect PC1 console to the console port of Router 1. ii. On PC1, start kermit. iii. Enter set line /dev/ttys0 iv. Enter set carrier-watch off v. Enter connect vi. You should now be connected to the router, enter enable and type in the password (on the board). vii. Type in the following: configure terminal interface fastethernet0/0 ip address end 4. Similarly Configure Router 2 - Router 4 with their IP addresses , , respectively

3 Part B DNS In this part, PC4 is set up as a DNS server. PC1-PC3 are run as regular hosts. All PCs will belong to the domain mylab.com and use the following assignment: Linux PC Domain Name IP Address PC1 PC1.mylab.com /24 PC2 PC2.mylab.com /24 PC3 PC3.mylab.com /24 PC4 PC4.mylab.com /24 Configuration: 1. Make sure the file /etc/resolv.conf is empty. 2. Make sure named is not running by typing pkill named. 3. Run the following on each PC: a. cd ~/namedpackage b. chmod 755 named-installpc1 (or PC2, PC3, etc ) c../named-installpc1 (or PC2, PC3 ) On PC1-PC3: 1. Verify /etc/nsswitch.conf contains line hosts: dns files 2. Create /etc/resolv.conf with line nameserver Verify /etc/hosts contains localhost.localdomain localhost 4. You may need to run /etc/rc.d/init.d/network restart On PC4: 1. cp /etc/named-part3.conf /etc/named.conf 2. /etc/rc.d/init.d/named start SAVE DATA save the output of the following commands: On PC4: 1. host v PC3.mylab.com 2. host v host v localhost 4. host v tcpip-lab.net On PC1: 5. host v PC3.mylab.com 6. host v host v localhost 8. host v tcpip-lab.net Next, we will examine the exchange of DNS messages between DNS resolvers and DNS servers. On PC1 1. Open the terminal and type: ifconfig eth1 up 2. Make sure you have connected eth1 of PC-1 to port 23 of the switch 3. Start wireshark and listen on eth1. Make sure MAC name resolution, network name resolution, and transport name resolution are disabled. 4. Observe the network traffic caused by issuing the following command: ping c 3 PC3.mylab.com ping c 3 localhost ping c 3 tcpip-lab.net ping c 3 PC3.mylab.com SAVE DATA save the detailed traffic observed in wireshark to a file.

4 Part C Hierarchy of DNS Servers In real life, a single name server will not maintain entries for all addresses. DNS was designed to be a distributed system, and in this part we will see how multiple name servers interact to lookup and share address mappings. We will use the following hierarchy: root. top level domains.com.net.mylab.com.lab9.net We will use the following assignment of IP addresses to domain names: Linux PC IP Address Domains Domain Server for DNS Zones PC root-server.net. PC top-server.com.com PC top-server.net.net lab8.net PC nameserver.mylab.com mylab.com Router IP Address Domain Names Name Server Router R1.mylab.com PC Router R2.mylab.com PC Router R3.lab9.net PC Router Router4.com PC

5 Configuration: PC1-PC4 1. Clean up files from previous exercises: Delete or comment out all lines in /etc/hosts Make sure /etc/resolv.conf is empty 2. Copy /etc/named-part6.conf to /etc/named.conf and restart named Router1-Router4 1. enable 2. configure terminal 3. ip name-server ip_address_of_nameserver (see table above for each router) 4. ip domain-lookup 5. end 6. show hosts 7. clear host * Now we are ready to examine how DNS queries are resolved in a hierarchical system. 1. On PC1, Make sure that eth1 is up and has been wired to port 23 of the switch. Start a wireshark session listening on eth1. 2. Run the following ping commands from the routers: SAVE DATA save the traffic observed in wireshark after each command to a file On Router 1: 1. ping R2.mylab.com 2. ping R3.lab9.net 3. ping Router4.com On Router 3: 4. ping R1.mylab.com 5. ping Router4.com 6. ping root-server.net On Router 4: 7. ping R3.lab9.net Kill the root nameserver on PC1. Restart the nameserver on PC4. On Router 2: 8. ping R3.lab9.net Reset all routers with the reload command. Do NOT save modified config!!! Remember to save all your files from the PCs, then please shutdown!

6 Questions (8 x 10 = 80 points) Part B Attach 9 files (8 host v command outputs, 1 wireshark trace) 1. Explain and interpret the output of the host v commands run on PC4. For the following, refer to the wireshark trace: 2. Did all 4 ping commands generate a DNS message? 3. What happens if a DNS query that cannot be resolved is issued? Were all of the queries in the trace resolved? 4. When you repeated the ping to PC3, did PC1 issue another DNS request or was the previous response cached? Part C Attach 8 files (wireshark traces) For the following, refer to the wireshark traces: 1. For each command, explain how the observed DNS queries are resolved. 2. Which queries have the recursion-desired flag set? 3. List the authoritative servers for the.net and.com domains. 4. Do you observe recursive or iterative DNS queries, or both? What are the advantages/disadvantages of each?