CS 15-441 Fall '01
Project 2

Handout ( [ps], [pdf], [single html], [split html] )

Simulator handout ( [ps], [pdf], [single html], [split html] )

Project 2 has been graded. We have some grading information.

Out: Tuesday, Oct. 2
Due: Tuesday, Oct. 30, 5PM

Late Policy:

• 10% off till Oct. 31, 5pm
• 20% off till Nov. 1, 5pm
• no credit after that

Hints:

• RCS tutorial / CVS links
• The TCP version included in the simulator does not generate packets that have the PUSH, RST, or URG flag set. Nonetheless, your firewalling implementation should to be able to filter packets based on these flags.
• The implementation of TCP in the simulator differs in some points from the requirements listed in RFC 793. However, these differences do not have any influence on the project and you can ignore the rest of this note. For people already familiar with TCP, the differences are:
  • Sequence numbers are per packet, not per byte.
  • Acks and data are never sent in one packet.
  • Acks have the sequence number field set to zero.
  • Data packets have the acknowledgment number field set to zero.
• The TCP and UDP send functions already allocate space for the IP header so there is no need to allocate space again in the IP layer. The p_data member of the pbuf passed to ip_output() points to the space for the IP header.
• We've provided sample implementations of the DHCP client and server in the utils directory. You can use them to test your implementation.

Handin:

1. Send an email listing the two group members to uhengart+441@cs.cmu.edu. The format of the body of this email is described in the project handout.
2. Each group member should execute "cklog cs.cmu.edu" from an Andrew machine.
3. Wait till you get an email saying that your handin directory has been set up for you. If you do not get an email within 24 hours after executing step 2, send email to uhengart+@cs.cmu.edu.
4. Copy your source files, your Makefile, and your project report to your handin directory. The two group members have full access to their handin directory, so you can modify the files you handed in if required. You might have to execute "cklog cs.cmu.edu" again before being able to access the directory.

• Do not hand in any executables or object files.
• Hand in only one version of your code.
• When executing gmake in your handin directory, the following executables (and the corresponding object files) must be generated: kernel, setfilter, setnat, dhcp_client, and dhcp_server.
• The compilation/building process must not result in any warnings.
• The compilation/building process must not build binaries that are purified or that use some other debugging, verification,... tool. It is ok to compile/build with the -g option.
• Your makefile must use gcc (not cc).

Questions and Answers:

Revisions and Updates:

Project Handout

• Section 4.1:
  • The syntax for the dsize rule option should look as follows: dsize: [<|>] < number>. The syntax given in the handout is missing the colon.
  • The example rule should look as follows:

    input: tcp 1.2.3.4 any -> 5.6.7.8 80 (flags: SF; ttl: 30;). The rule given in the handout is missing a semicolon.

  • The TTL check should be done after the TTL is decremented by the forwarding code.
• Section 5: NAT for packets on the return path should be done before the routing decision is made. The NAT box shown in Figure 4 denotes only where the translation from private to public addresses takes place, but not where the translation in the reverse direction takes place.
• Section 6:
  • The DHCP client should use the value of the lease_length command line parameter for an IP Address Lease Time option in DHCPDISCOVER and DHCPREQUEST messages.
  • The release time of an assigned address is computed by the client as the startup time of the client plus the value of the release_time command line parameter.
  • Some guidance on implementing DHCP.

Simulator Handout

• Section 8.2: Broadcast packets are delivered only to UDP sockets, never to TCP sockets.

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