6.10 Exercises

6.10 Exercises

1. Represent each address below in binary format. What is the class of each address?

   1. 192.12.102.0

   2. 10.20.30.100

   3. 130.5.77.15

2. For each of the following address/prefix length pairs, give its natural mask (in dotted-decimal notation), its subnet/supernet mask (also in dotted-decimal notation), and the range of networks or subnets permitted by the mask. Also describe any problems and limitations with the address/mask pairs, if any.

   1. 129.99.0.0/16

   2. 136.178.0.0/22

   3. 198.9.9.0/28

   4. 192.92.240.0/20

   5. 192.92.243/20

3. Subnet 136.178.0.0 into 16 subnets. Show the binary and dotted-decimal forms of each subnet, as well as the subnet mask.

   Refer to Figure 6.29 (p. 294) for Exercises 4 through 7.

   
   Figure 6.29: Diagram for Exercises 4 through 7.

4. Where are the FAs for this network design?

5. Where are the potential logical and physical boundaries for this network design?

6. Given the network address 129.99.0.0/16, develop a variable-length addressing scheme that best fits the design, with the following numbers of users:

   AS Number	Location	Department	Users
   1	Chicago Campus Building 1	Legal	120
   		Accounting	370
   	Chicago Campus Building 2	HQ	1580
   		Engineering	200
   2	Toronto	Sales	75
   	Boston	Sales	110
   3	Philadelphia	Operations1	2150
   		Operations2	975
   		Sales	575

7. You are using BGP4 in the WAN between AS1, AS2, and AS3. Describe in plain text or as BGP4 policy statements how you would achieve the following:

   1. Permit AS3 to communicate with AS1 but do not allow AS2 to communicate with AS1.

   2. Allow both AS2 and AS3 Internet access through AS1 only between 6 PM and 6 AM EST each night.

   Refer to RFC 1771 for specifics on the BGP4 specification.

8. Consider the following: You are an ISP and have a group of addresses (CIDR blocks) to allocate to your customers. You have allocated addresses to a number of customers from a CIDR block of 198.9.128.0/18 (equivalent to the block of Class C addresses 198.9.128.0 through 198.9.191.0). Now one of your clients wants to stop using your ISP service and wants move to another ISP while keeping the /24 that you had allocated to it (198.9.145.0/24). You are in a dilemma; you cannot take back this address (your customer's lawyers are better than yours!), yet advertising a CIDR block that contains that address seems to break the rules of CIDR routing.

   1. Show how routing based on the longest (most specific) match allows you to continue advertising this CIDR block.

   2. Show what happens to the ex-customer's traffic if there is a bug in the Internet and their route gets dropped.

9. Many network designs are requiring redundant access to the Internet, with the backup connection either in a hot-standby mode or load balancing between the two connections. Using BGP4, outline a strategy for providing a backup Internet connection for the following cases:

   1. The backup Internet connection is in a hot-standby mode and can be made operational with a change in the routing configuration.

   2. The backup Internet connection is fully operational, and there is load balancing between the primary and backup connections.