CS 434L/534L Laboratory Manual

The following is a list of topics covered in CS434L. Lab sessions are nominally two hours. The objective is for the students to confirm by their own observations the statements that they had heard earlier in the lectures.

• Lab 1: Ethernet Networks: ARP and PING
  Working in pairs, students connect their computers into an Ethernet, using "ifconfig" to assign private ("darknet") IP addresses to the interfaces. The protocol analyzer "Ethereal" is used to investigate the content of the sequence of frames that occurs when one of the computers "pings" the other (ICMP echo request and echo reply). The Address Resolution Protocol (ARP) messages and the resulting entries in the ARP caches are also investigated.
• Lab 2: Client-Server: UDP and TFTP
  This lab session provides an introduction to client-server systems. Again students work in pairs, with one of their computers configured as a Trivial File Transfer Protocol (TFTP) client and the other as a TFTP server. TFTP runs on top of the User Datagram Protocol, which is connectionless and therefore relatively simple. Students use Ethereal to investigate the content of the frames that are exchanged during transfer of a file to/from server from/to client. The time taken for transfer of a large file is measured.
• Lab 3: Client-Server: TCP and FTP
  This lab session is again a client-server investigation, this time the File Transfer Protocol (FTP), which runs on top of the Transmission Control Protocol (TCP). TCP provides virtual connection transport service, so this is a more complex situation in which the students observe the establishment, use, and destruction of the virtual connections. FTP, using sliding-window flow control, is a more sophisticated protocol than TFTP; this shows up in the reduced file-transfer times, which are measured and compared to those obtained in lab session #2. An FTP server also requires client identification; students observe this using Ethereal, noting that the password is clearly visible on the Ethereal trace during transit from client to server.
• Lab 4: Static Routing
  In this lab session a router is introduced for the first time. Students work in groups of four, enabling them to use four computers build a two-network internet. All interfaces must be configured, and appropriate entries made in the routing tables of all computers. The file-transfer time across the router is measured and compared to the time measured in lab session #3 to see if transit through a router significantly slows the file transfer. The Maximum Transfer Unit of one of the router interfaces is reduced to force fragmentation of IP datagram, which is observed using Ethereal.
• Lab 5: Packet-Filtering Firewall
  The router configuration used in lab session #4 is enhanced to provide packet-filtering, which is the basis of firewalls. Students experiment with the settings of the packet filter, and observe which types of access are blocked and which are permitted. Passive-mode FTP is introduced during these experiments. Finally, "Masquerading" is activated on the packet filter, implementing Network Address Translation.
• Lab 6: Route Tracing and Dynamic Routing
  An internet of three networks is formed by connecting four computers in the pattern workstation-router-router-workstation. The routers are first configured manually, and "traceroute" and "ping -Rv" are used to demonstrate route tracing (trivial in this case, but preparing for lab session #7). The presence of two routers along the path gives the opportunity for more measurements of the speed penalty imposed by routers during file transfer. The Routing Information Protocol is then activated, and students observe how the computers learn from each other by exchanging routing information.
• Lab 7: Domain Name Service and Wide-Area Networking
  In this session the Instructional Network Lab is connected to the outside world for the first time, through a firewall with Network Address Translation. Students work individually to explore naming systems, first using the "hosts" table in their workstation, then using the Domain Name Service (DNS). There is a detailed investigation of the functioning of DNS, including exploration of alternative DNS servers. The students use "traceroute" to determine the path followed by IP datagrams to a distant destination, such as Purdue University.
• Lab 8: HyperText Transfer Protocol and the World-Wide Web
  Using a Netscape browser, students obtain Ethereal traces to see establishment of multiple TCP connections to download the HTML page and the embedded images of a World-Wide Web page. Access to an E-commerce site exhibits Set-cookie response headers and Cookie request headers. Students observe the switch from TCP port 80 to port 443 when SSL/secure HTTP (https) is invoked, and see encrypted traffic on the Ethereal trace.