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Chapter 7 - Variable Length Subnet Masking (VLSM)

Cisco & IP Addressing
Louis D. Rossi, Louis R. Rossi and Thomas Rossi
  Copyright © 1999 The McGraw-Hill Companies, Inc.

Answers
  7.1: VLSM is variable-length masking, which allows different subnet masks to be used for the same major network.
  7.2: VLSM preserves addressing space.
  7.3: VLSM can only be used with a classless routing protocol.
  7.4: One addressing solution is as follows; yours may be different:
Serial Links
Wire 192.16.15.4 to the JAX-SANFRAN link
Wire 192.16.15.8 to the JAX-NYC link
Wire 192.16.15.12 to the JAX-TAMPA link
Wire 192.16.15.16 to the JAX-DALLAS link
Router JAX Serial Addresses
S0
192.16.15.5/30
255.255.255.252
S1
192.16.15.9/30
255.255.255.252
S2
192.16.15.13/30
255.255.255.252
S3
192.16.15.17/30
255.255.255.252
Router SANFRAN
Use the mask of 255.255.255.224 on the Ethernet link.
S0 address of 192.16.15.6
E0 address of 192.16.15.65
Host address range 192.16.15.65 – 199.16.15.95
Wire address of 192.15.15.64
Router NYC
Use the mask of 255.255.255.240 on the Ethernet link.
S0 address of 192.16.15.6
E0 address of 192.16.15.49
Host address range 192.16.15.49 – 199.16.15.63
Wire address of 192.15.15.48
Router TAMPA
Use the mask of 255.255.255.240 on the Ethernet link.
S0 address of 192.16.15.14
E0 address of 192.16.15.33
Host address range 192.16.15.33 – 199.16.15.47
Wire address of 192.15.15.32
Router DALLAS
Use the mask of 255.255.255.192 on the Ethernet link.
S0 address of 192.16.15.18
E0 address of 192.16.15.129
Host address range 192.16.15.129 – 199.16.15.191
Wire address of 192.15.15.128
Router JAX
Use the mask of 255.255.255.192 on the Ethernet link.
E0 address of 192.16.15.193
Host address range 192.16.15.193 – 199.16.15.254
Wire address of 192.15.15.192
  7.5: The 255.255.255.252 mask is called the serial mask because it only allows for two hosts, which is only practical for serial links.

 


 
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