Homework 4: Resource Allocation and IP

Goals: 

• Practice reasoning about algorithms for resource allocation and IP address management. 
• Work through a few examples.
• Learn to use standard tools for getting information about IP address assignments and allocations.
• Exercise your creativity and analogical thinking.

Contents: 

• Part A: Resource allocation (25%)
• Part B: Central abstractions (25%)
• Part C: IP basics (25%)
• Part D: Mapping the IP address space (25%)
• Submitting your work

Part A: Resource allocation (25%)

• P&D 6.28 (TCP congestion control)
• P&D 6.39 (buffering)
• P&D 6.46 (application taxonomy)
• P&D 6.50 (RSVP soft state)

Part B: Central abstractions (25%)

In class on Wednesday, March 14, we discussed the robustness and fragilities of the IP protocol as the central abstraction for the Internet, as well as those of sewing and electricity. We drew an hourglass-shaped figure with IP at the center, applications and transport protocols above, and data link protocols and physical media below. (If you weren't in class, come talk with me during office hours or get a classmate to explain what we talked about. It's not in any of the readings.)

Develop your own "hourglass analogy":

1. Draw an hourglass diagram representing a system of your choice (not discussed in class) that includes a single central abstraction.

2. What robustness is enabled by the central abstraction?

3. What fragilities result from the central abstraction?

4. In terms of your answers to 2 and 3, how does this system compare to the Internet and IP?

Part C: IP basics (25%)

• P&D 4.4 (fragmentation)
• P&D 4.5 (fragmentation)
• P&D 4.13 (ARP)
• P&D 4.40 (subnets)

Part D: Mapping the IP address space (25%)

The xkcd comic, "Map of the Internet: The IPv4 space, 2006," provides an interesting but necessarily incomplete visualization of the IPv4 address space allocation. We'll use a few standard tools to extend this visualization to include a few personally significant landmarks.

Before you begin, make your own copy of the comic strip to annotate (either by saving a digital copy and opening it in an image editor, or by printing it out).

Note that the large /8 subnets in the upper left corner correspond to class-A address blocks. These were allocated somewhat on the basis of beliefs about who would be likely to use that many addresses, but I think it was more a matter of who got there first in the early days of the Internet. (There are not many class-A blocks to go around!) 

You'll also note that many familiar names on the WWW are in the section labeled USA & Canada, in the class-B blocks.

1. Use the tool nslookup to find the IP address associated with the hostname www.grinnell.edu. (Specifically, type "nslookup www.grinnell.edu".) What is the address?

2. Use the tool whois to find out more about the organizational records associated with this IP address. (Specifically, type "whois <address>".)You'll note that one entry is for the associated CIDR block. What is the CIDR block? What IP address class does it correspond to? 

3. Add Grinnell College to your copy of the xkcd map of the Internet.

4. Use nslookup and whois to find the IP address and associated CIDR block for www.one-eyed-alien.net, which is my personal web server at home. Report this information. According to whois, what organization is my IP address associated with? What do you think is happening here?

5. Add www.one-eyed-alien.net and the organization from step 4 to your map.

6. Use nslookup and whois to find the associated IP address and CIDR block, and the organization that owns the CIDR block, for www.grinnellplans.com. Report and map this information.

7. Repeat step 6 for at least one more hostname of your choice. Note anything you see that's unexpected.

We'll experiment more with tools such as nslookup and whois in the next homework.

Submitting your work

Please turn in your work ON PAPER at the beginning of class on the due date. This will be the normal procedure for submitting homework.

I would appreciate an estimate of how long you spend on this assignment so that I can try to keep homework assignments to a reasonable size.

Janet Davis (davisjan@cs.grinnell.edu)