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.