Homework 7

1. You are the CTO of a growing startup and have to get IP addresses to connect 560 computers to the Internet. You can get IP addresses from two providers, IPMart and EastSideIP. IPMart sells classA, class B and class C blocks, while EastSideIP sells CIDR blocks. As the IPv4 address space is scarce, you want to save money and get the smallest number of addresses possible.

  • a. If you get one block from IPMart, which class do you have to get? What is the problem with that?
  • b. If you get one block from EastSideIP, how many bits are there in the mask (e.g., is it a /8, /22)? How many addresses are wasted?
  • c. Suppose you can get two blocks from EastSideIP, and they can be of different sizes. How many bits are there in the masks for each of the blocks? How many addresses are wasted now?

2. Another customer of EastSideIP =needs to get 8000 IP addresses. You work for =EastSide, and see that you have the address range from 128.140.80.0 to 128.140.127.255 available.

  • a. What is the best CIDR block from this range you can allocate the customer?
  • b. Why is it best to minimize the number of CIDR blocks you allocate?
  • c. Why is it best to also minimize the size of the address blocks?

3. Suppose you have the following routing table in your router

Destination Netmask NextHop Interface
0.0.0.0 0.0.0.0 100.10.1.1 eth0
128.148.0.0 255.255.0.0 128.148.0.1 eth1
128.148.32.0 255.255.240.0 128.148.32.1 eth2
128.148.34.128 255.255.255.128 128.148.34.129 eth3

What is the next hop for each of these addresses, given that you use longest-prefix matching?

  • a. 128.148.34.143
  • b. 128.148.34.12
  • c. 128.148.38.1
  • d. 200.192.120.12
  • e. 128.148.12.2
  • f. 128.140.0.1

Solutions

Topic revision: r1 - 2013-11-07 - JimSkon
 
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