COMPUTER NETWORKING LAB EXERCISES (TP) 1 BASIC CONFIGURATION AND TOOLS FOR EVERYBODY:

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1 Name 1: Name 2: Group number: COMPUTER NETWORKING LAB EXERCISES (TP) 1 BASIC CONFIGURATION AND TOOLS FOR EVERYBODY: PING(6), DIG, TRACEROUTE(6), NETSTAT September 24, 2012 Abstract In this TP you will familiarize yourself with the Internet Engineering Workshop (IEW) lab room and equipment. You will learn how to configure machines in order to achieve IP connectivity within a Local Area Network (LAN). You will also learn how to configure a machine to access the Internet, and practice some networking commands that enable you to obtain information about Internet machines and about the connectivity and the paths between them. 1 ORGANIZATION OF THE TP Each group of two students works on one workspace. There are two computers per workspace. The workspace number is written on the white stickers tagged to each computer. 1.1 TP REPORT Type your answers in this document during the TP. That will be your TP report (one per group). When you finish print the report. Don t forget to write your names and group number on the first page of the report. The deadline is October 4, before the lecture. One TA will be in the lecture room to collect the reports. If you can not attend the lecture you can bring it before to any TA s office. 2 IDENTIFY IEW ROOM EQUIPMENT AND YOUR WORKSPACE The hardware equipment in the IEW room is shown in the figure below. Each workspace consists of one local hub and two Linux PCs: one workstation PC and one router PC (the notation for PCs can be found on the stickers on each PC). Local hubs are placed next to the monitors and keyboards of your PCs. There is also one central hub, usually placed next to the windows, and used to connect multiple 1

2 workspaces when required by an experiment. There are actually a few parallel configurations as the one shown on the figure below, each having its own central hub. Existing networking hardware in the room Though not shown in the figure above, there are also a few EPFL hubs that are connected to the EPFL s network and used when the computers need to be connected to the Internet. These hubs are positioned on the upper part shelves and are shared by a few neighboring workspaces. To interconnect the equipment you will use up to 3 short and 1 long 10BaseT cables at one workspace. Identify all the mentioned equipments and your workspace, before you start the actual work. 3 CONVENTION The upper logo on the left means you should do the corresponding commands/actions on the workstation PC. The second logo on the left is for the router PC. 2

3 4 BASIC CONNECTIVITY WITHIN A LAN In this section you will learn how to configure machines in order to achieve IP connectivity within a Local Area Network (LAN). You will also use wireshark to observe which traffic is sent (or not) in some scenarios. This will help you to find what is configured correctly and what has to be configured additionally in order to achieve the connectivity. A group will use the two PCs at their workspace to form a LAN that corresponds to a company site LAN. The EPFL hub simulates a Wide Area Network (WAN) of the company. In the Lab Exercise 2 you will also configure manually routers to achieve interconnection between the sites. This week we focus on LAN connectivity. 4.1 PUT BOTH PCS INTO A PROPER INITIAL NON-CONFIGURED STATE In order to put the machines into a clean initial non-configured state, click twice on the Network Workspace Manager icon that you can find on the desktop of each machine. From the menu that opens select Load from Disk and choose lab-1-default: IEW default configuration for lab1. Furthermore, to stop linux network services issue the following command from terminal on both machines. #/etc/init.d/networking stop 4.2 WIRING Wire your PCs as shown in the following figure: Figure 1: Wiring of the hardware equipment for the lab. 3

4 4.3 ADDRESSING SCHEME We use the following convention for writing IP addresses in the rest of this document: X - the number of your workspace - you should find out which value should be used instead of Identify your workspace number (the workspace number is written on the white stickers tagged to the computers). What is your workspace number? For IPv4 addressing we have at our disposal the private IPv4 address space from to For the local network at your site, we will use the IPv4 network address [100 + X].0/24 (X is the number of your workspace). The host identifier (the fourth byte) should be 1 to indicate the router PC and 2 for the workstation PC. The IPv4 network address of the interconnection network is /24. On this network, the host identifier of the router s IPv4 address corresponds to [100 + X]. How many IPv4 networks does your router PC belong to? Name the type of the network(s). (1 point) Write down the IPv4 addresses you will use for the interfaces according to this addressing scheme. (1 point) Workstation PC: Router PC LAN (eth1): Router PC WAN (eth0): Several IPv6 addresses can be obtained by each interface. You will observe link-local IPv6 addresses obtained automatically by IPv6 Stateless Address Autoconfiguration. Furthermore, you will use manually configured IPv6 addresses: For the local network at your site, we will use the IPv6 address 2002:80b2:9cdc:X02::1/64 for the router PC and 2002:80b2:9cdc:X02::2/64 for the workstation (X is the two-digit number of your workspace). The IPv6 network address of the router s WAN interface is 2002:80b2:9cdc::X01:1/64 (X is the twodigit number of your workspace). 4

5 Write down the IPv6 addresses you will use for the interfaces according to this addressing scheme. (1 point) Workstation PC: Router PC LAN (eth1): Router PC WAN (eth0): As mentioned before link-local addresses will also be present because of IPv6 Stateless Address Autoconfiguration (SLAAC). For calculation of these addresses MAC addresses of the interfaces are needed. To find it, for eth1 interface for example, look at the HWaddr field after issuing the command: #ifconfig eth1 Write down the MAC address of the interfaces. (1 point) Workstation PC: Router PC LAN (eth1): Router PC WAN (eth0): SLAAC IPv6 link-local address is formed as follows. The address prefix is fe80::/64. For the host part, we use a 64-bit interface identifier in modified EUI-64 format. It is derived from the interface s MAC address by setting 7th bit to 1 and inserting ff:fe in the middle. Illustration is given in Figure 2 adapted from Wikipedia page dedicated to IPv6 address. What are the IPv6 link-local addresses you expect based on the previous question and given explanations. Write the answer only for the interfaces below. (1 point) Workstation PC: Router PC LAN (eth1): 4.4 ARE YOU CONNECTED? USE WIRESHARK TO SEE WHAT HAPPENS. In order to have access to the commands that manipulate the network interfaces, you need to be logged in as superuser (root). You can do this by double click-ing on the Terminal icon on the Desktop of each machine (router PC and workstation PC). 5

6 Figure 2: Formation of EUI-64 starting from MAC address of an interface. To test IPv4 connectivity run a ping to the router from a terminal on the workstation. #ping [100 + X].1 (X is your workspace number) What is the ping error message? (1 point) ping message: To test IPv6 connectivity run a ping6 to the router s two IPv6 addresses of the same interface eth1 from a terminal on the workstation. X rt IPv6 link-local is the link-local IPv6 address of the router s eth1 interface you composed above. #ping6 -I eth0 X rt IPv6 link-local #ping6 2002:80b2:9cdc:X02::1 Please note that due to the kernel version it is necessary to specify the interface when pinging link-local IPv6 addresses. What is the ping error message? (1 point) ping message: On the router, run wireshark to observe the traffic of the link between the two machines belonging to your workspace. The wireshark program is used to capture the incomming and outgoing traffic on a network interface. In order to be able to run wireshark, you first have to put the interface up. #ifconfig eth1 up #wireshark -i eth1 & The following window will appear: 6

7 Open the Capture/Options menu and configure the options as indicated in the figure below. Then click Start. From a terminal on the workstation, activate the interface eth0 first an then run a ping to the router. #ifconfig eth0 up #ping [100 + X].1 (X is your workspace number) 7

8 What do you observe? Has the analyzer captured anything? (1 point) ping message: Captured traffic: From a terminal on the workstation, run a ping6 to the two IPv6 addresses of the router. #ping6 -I eth0 X rt IPv6 link-local #ping6 2002:80b2:9cdc:X02::1 What do you observe? Has the analyzer captured anything? (1 point) ping message: Captured traffic: To see the network interfaces of the workstation, type: #ifconfig -a What can we deduce form the above tests and displayed interface information? (2 points) 4.5 CONFIGURING AND TESTING OF THE LAN In previous question you observed that there exists IPv6 connectivity within the LAN. This is a consequence of IPv6 Stateless Address Autoconfiguration. However, these addresses are not globally routable. To obtain full IPv6 connectivity and IPv4 connectivity some additional steps are required CONFIGURATION OF THE NETWORK INTERFACE OF THE WORKSTATION PC The first step in order to achieve full connectivity from your machine is to configure its network interface and to assign an IP address to the interface. This is true both for IPv4 and IPv6 as link-local IPv6 addresses are not routable on the Internet. On the workstation, type: 8

9 #route -n #route -A inet6 to visualize the IPv4 and IPv6 routing tables of the machine. To configure your network interface and assign an IPv4 and an IPv6 address to it, type: #ifconfig eth [100 + X].2 netmask #ifconfig eth0 inet6 add 2002:80b2:9cdc:X02::2/64 where eth0 is the name of the network interface, [100 + X].2 is the IPv4 address, 2002:80b2:9cdc:X02::2 is the IPv6 address, X is your workspace number and and /64 are IPv4 and IPv6 netmasks. Which modifications were made to the routing table? [Notice there should be some modifications.] What are the new modifications used for? (1 point) Why do we need the netmask in the commands above? Explain. (1 point) How can we compute the host part of an IPv4 address? Give an example with the IPv4 address of your computer and its associated netmask. (1 point) Look again at the interfaces of your machine: #ifconfig -a 9

10 How many interfaces can you find? What are their names and what do they correspond to? What are the IPv4 and IPv6 addresses and netmasks of these interfaces? (1 point) There is an MTU (Maximum Transfer Unit) field for each interface. What is its value for each of the interface? Why is it not the same for all interfaces? (1 point) Run another ping to the router s local IPv4 interface: #ping [100 + X].1 What is the ping error message? Which traffic has been captured by the analyzer? (NOTE: Your analyzer should capture some traffic. If this is not the case, check if the cable connecting the router and workstation is plugged into the proper interface (eth1) of the router, by trying to plug it into another interface and repeating the ping command.) (1 point) ping message: Captured traffic: What can we deduce? (1 point) Run another ping6 to the router s local IPv6 interface: #ping6 2002:80b2:9cdc:X02::1 What is the ping6 error message? Which traffic has been captured by the analyzer? (NOTE: Your analyzer should capture some traffic. If this is not the case, check if the cable connecting the router and workstation is 10

11 plugged into the proper interface (eth1) of the router, by trying to plug it into another interface and repeating the ping6 command.) (1 point) ping6 message: Captured traffic: What can we deduce? (1 point) CONFIGURING OF THE ROUTER S NETWORK INTERFACES To see the mapping between IPv4 addresses and MAC addresses take a look at the arp table of the workstation: #arp -a To see the mapping between IPv6 addresses and MAC addresses: #ip -6 neighbor show Configure the router s interface eth1 according to the addressing scheme defined previously. #ifconfig eth [100 + X].1 netmask #ifconfig eth1 inet6 add 2002:80b2:9cdc:X02::1/64 To verify the configuration, type: #ifconfig eth1 Proceed in the same way to configure the router s interface eth0: #ifconfig eth0 up #ifconfig eth [100 + X] netmask #ifconfig eth0 inet6 add 2002:80b2:9cdc::X01:1/64 Now, the router should be reachable from the workstation for both IPv4 and IPv6 cases. Verify it by typing: #ping [100 + X].1 #ping6 2002:80b2:9cdc:X02::1 11

12 Which frames circulate on the network? (1 point) Check again the IP address-mac address mappings: #arp -a #ip -6 neighbor show Explain what changed in the arp table of the workstation? What made these changes happen? Whose MAC address do you find there? (1 point) At this point you should have both IPv4 and IPv6 connectivity within the LAN. Now try to reach the router s outside interface eth0 from the workstation: For IPv4: #ping [100 + X] Can you reach the router s IPv4 interface eth1 from the workstation? Why? (1 point) What is the message you get when trying to ping IPv4 address of a workstation that is not on the local network? For IPv6: #ping6 2002:80b2:9cdc::X01:1 Can you reach the router s IPv6 interface eth1 from the workstation? Why? (1 point) What is the message you get when trying to ping IPv6 address of a workstation that is not on the local network? 12

13 In both cases, why don t you see any frames on the network? (1 point) Add an IPv4 default route at the workstation (i.e. configure default gateway ) and do the same for IPv6: #route -n #route add default gw [100 + X].1 #route -n... #route -A inet6 #route -A inet6 add 2000::/3 gw 2002:80b2:9cdc:X02::1 #route -A inet6... Note that by adding a route to 2000::/3 we cover all currently global IPv6 addresses. Now, the router s outside interface should also be reachable from your workstation (for both IPv4 and IPv6). With this step you succesfully configured LAN network of your workspace. You will use the tools and principles seen up to now in the rest of this lab as well as in the following labs. 5 CONFIGURING A MACHINE TO ACCESS THE INTERNET AND TESTING YOUR CONNECTIVITY AND PATH TOWARD INTERNET HOSTS In this section, you will learn how to configure your computer in order to be able to access the Internet and surf Web pages. To surf the Web, in addition to the configuration seen in the previous part of this TP, you will also have to configure your machine to use DNS (Domain Name System). You will practice some commands for getting information about Internet hosts, their connectivity and paths between them. In order to have connectivity with the rest of the world it is necessary to configure the default gateway on the router PC also. To this end use the same commands as above. For IPv4 use as the default gateway and for IPv6 2002:80b2:9cdc::bbbb:1. Furthermore, a station with multiple interfaces is not a router. To turn it into a router, it is necessary to activate the IPv4 and IPv6 forwarding processes in the kernel. On the router, type: #sysctl -w net.ipv4.ip forward=1 #sysctl -w net.ipv6.conf.all.forwarding=1 13

14 5.1 PART I - IPV4 In this section we would like to explore network behavior when only IPv4 Internet connectivity is present. #ifconfig eth0 down #ifconfig eth0 up #ifconfig eth [100 + X].2 netmask #route add default gw [100 + X].1 To check if you are connected to the Internet, you can use the ping command: #ping -c 5 Try also: #ping -c Discuss the outcome of the two tests? (1 point) The check the DNS settings on your machine, open the file /etc/resolv.conf and verify that the following lines are present: nameserver search iew.epfl.ch If they are not, use a text editor and put the correct entries listed above (do man gedit if you do not know any other linux text editor). Now you should be able to access the Internet. Try: # ping -c 5 Write the average RTT you obtained (1 point): dig is a command-line tool for querying Domain Name System (DNS) name servers. Use it to find A (IPv4) record concerning lca.epfl.ch. 14

15 # dig lca.epfl.ch A Write down the IPv4 address you found (1 point): traceroute is a tool for displaying the route to a destination. # traceroute Write the result of the traceroute command (1 point): At the end, open the Konqueror web browser (Figure 3), go to lca.epfl.ch, and leave the browser open for the moment. Look at the active TCP connections. # netstat -t -n Write down the output (1 point): 15

16 Figure 3: Konqueror web browser shortcut. 5.2 PART II - IPV6 Now let s examine the situation when only IPv6 connectivity is present. #ifconfig eth0 down #ifconfig eth0 up #ifconfig eth0 inet6 add 2002:80b2:9cdc:X02::2/64 #route -A inet6 add 2000::/3 gw 2002:80b2:9cdc:X02::1 Knowing that the DNS server is available at the address 2002:80b2:9cdc::aaaa:1 open the file /etc/resolv.conf and update it accordingly. You should have now IPv6 Internet connectivity. Try: # ping6 -c 5 Write the average RTT you obtained and comment on the obtained value having in mind the result from 16

17 subsection 5.1 (1 point): Use dig it to find AAAA (IPv6) record concerning lca.epfl.ch. # dig lca.epfl.ch AAAA Can you find the correlation between A (IPv4) record from subsection 5.1 and AAAA (IPv6) record (1 point)? Repeat the test with the traceroute command from subsection 5.1 Use the IPv6 version of the command (traceroute6). # traceroute6 Write the result and your observations having in mind the result from subsection 5.1 (1 point): Now, open the Konqueror web browser (new window), go to lca.epfl.ch. 17

18 Is there a difference between two versions of lca.epfl.ch pages? (1 point) Look at the active connections. # netstat -t -n Write down the output? (1 point) 5.3 PART III - IPV4 AND IPV6 Let s see what happens when both IPv4 and IPv6 Internet connectivities are present. #ifconfig eth [100 + X].2 netmask #route add default gw [100 + X].1 Open the Konqueror web browser (new window), go to lca.epfl.ch. Which version of the web site did you get? (1 point) Try to open and look at the active connections. # netstat -t -n 18

19 Having in mind previous outputs of netstat which version of ETHZ web site did you access? Explain. (1 point) 6 CLEAN-UP YOUR WORK SPACE Reboot the PCs by typing: # reboot Unplug the 10BaseT cables and disconnect the power plug of your hub. Leave the long cable on the desk and connect the router and workstation PC to the hub located between the machines (i.e., leave the workplace in exactly the same condition you have found it). 7 CONCLUDING QUESTIONS You can answer these questions without being in the lab, assuming you already did the above part of the TP. Why do we need to the configure the network interface? (1 point) What do we configure? (1 point) 19

20 Why do we have domain names? (1 point) Do we have a domain name server-like in the telephone network? Explain. (1 point) Why are routers used to interconnect LANs of a company network, i.e. why it is not always good enough to simply expand to a big LAN by using bridges and adding new Ethernet segments? Explain the problems and how they are solved by using routers. Hint: think of arp, mac addresses, STP topology. (3 points) 20