CS 6250 - Computer Networks

Homework 3 - Assigned: Wednesday, 28 September Due: Wednesday, 5 October In Class

You should prepare answers to the following questions on paper and submit them to me during class. Solutions may be handwritten, as long as I can read your handwriting.

  1. Consider a router that interconnects three subnets: Subnet A, Subnet B, and Subnet C. Suppose all of the interfaces in each of these three subnets are required to have the prefix 223.1.17/24. Also suppose that Subnet A is required to support at least 125 interfaces, and Subnets B and C are each required to support at least 60 interfaces. Provide three network addresses (of the form a.b.c.d/x) that satisfy these contraints. Also, provide a stable routing table for this router assuming only these networks are connected. Remember that /24 means the prefix has 24 bits.

  2. Now, consider that the edge router from the previous question has an additional interface (D) that is connected to a border router for the AS where this network is allocated. This border router provides Internet connectivity to the edge router as well as other routers and networks within the AS.
    1. Given that the Internet management rules require that network masks of at most 22 bits be advertised to BGP peers, give an example network address for this border router to advertise that will correctly support routes to and from the networks in problem 1.
    2. With this new connectivity, give possible stable routing tables for both the edge router of problem 1 and the border router introduced here.

  3. Describe how the messages and operation of BGP should prevent routing loops from occuring in the Internet. What types of loops should it prevent and what types of loops may still be possible?

  4. Read RFC 3882. What was the specific problem that this RFC describes? What are the proposed solutions?

  5. IPv6 is the proposed replacement for IPv4 which includes support for much larger addresses. Many have claimed that this solves the mobility problem and makes solutions like mobile IP unnecessary. Do you agree? Using what you have studied about routing and Mobile IP, provide a technically detailed argument to justify your answer.