6.1??“172.16.7.254
Introducing VLSMs
When an IP network is assigned more than one subnet mask for a given major network, it is
considered a network with VLSMs, overcoming the limitation of a ?¬?xed number of ?¬?xed-size
subnetworks imposed by a single subnet mask. Figure 3-30 shows the 172.16.0.0 network with
four separate subnet masks.
Figure 3-30 VLSM Network
VLSMs provide the capability to include more than one subnet mask within a network and the
capability to subnet an already subnetted network address. In addition, VLSM offers the following
bene?¬?ts:
?– Even more ef?¬?cient use of IP addresses: Without the use of VLSMs, companies must
implement a single subnet mask within an entire Class A, B, or C network number.
For example, consider the 172.16.0.0/16 network address divided into subnets using
/24 masking, and one of the subnetworks in this range, 172.16.14.0/24, further
divided into smaller subnets with the /27 masking, as shown in Figure 3-30. These
smaller subnets range from 172.16.14.0/27 to 172.16.14.224/27. In the ?¬?gure, one
of these smaller subnets, 172.16.14.128/27, is further divided with the /30 pre?¬?x,
172.16.14.64/27
172.
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