Solutions to Part A Planning

It's a good idea to keep the design as simple as possible, without making it so simple that it will not be useful as the network evolves. In this case, any subnet mask with at least 7 host bits would work, including the easy mask of 255.255.255.0. Any choice of mask between 255.255.224.0 and 255.255.255.128 would have allowed for 6 subnets and 100 hosts per subnet.

Table 16-3 shows one solution for the subnet numbers chosen, using mask 255.255.255.128, with Table 16-4 showing some sample IP address assignments.

Table 16-3 Part A: The Completed IP Subnet Planning Chart

Location of Subnet/Network Geographically

Subnet Mask

Subnet Number

R1 Ethernet

255.255.255.128

163.1.1.128

R2 Ethernet

255.255.255.128

163.1.2.128

R3 Ethernet

255.255.255.128

163.1.3.128

Serial between R1 and R2

255.255.255.128

163.1.12.128

Serial between R1 and R3

255.255.255.128

163.1.13.128

Serial between R2 and R3

255.255.255.128

163.1.23.128

Table 16-4 Part A: The Completed IP Address Planning Chart

Host

Address

PC11

163.1.1.211

PC12

163.1.1.212

PC13

163.1.1.213

PC21

163.1.2.221

PC31

163.1.3.231

PC32

163.1.3.232

SW1

163.1.1.211

SW2

163.1.1.212

SW3

163.1.1.213

R1-E0

163.1.1.201

R1-S0

163.1.12.201

R1-S1

163.1.13.201

R2-E0

163.1.2.202

R2-S0

163.1.12.202

Table 16-4 Part A: The Completed IP Address Planning Chart (Continued)

Host

Address

R2-S1

163.1.23.202

R3-E0

163.1.3.203

R3-S0

163.1.13.203

R3-S1

163.1.23.203

Server 1

163.1.1.1

Server 2

163.1.1.2

Server 3

163.1.2.3

As long as the numbers are in the right subnet, the actual IP addresses that you chose for your answer are fine. I just picked numbers between 200 and 209 for the last octet for router addresses, and between 210 and 239 for the switches and PCs. For the servers, I made the last octet match the server number. In real networks, you might reserve particular ranges of last octet values in each subnet for network overhead devices. For instance, all of your routers' LAN interface IP addresses might always be between 1 and 5.

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