For example, assume that the network administrator was also allowed to

configure the 130.5.0.0/16 network with a /26 extended network prefix,

as shown in Figure 17. A /16 network address with a /26 extended net 

work prefix would permit 1,024 subnets (210), each of which would

support a maximum of 62 hosts (26  2). The /26 prefix would be ideal

for small subnets with less than 60 hosts, while the /22 prefix would be

well suited for larger subnets containing up to 1,000 hosts. 

F I G U R E   1 7 .   1 3 0 . 5 . 0 / 1 6   w i t h   a   / 2 6   E x t e n d e d   N e t w o r k   P re f i x

Route Aggregation

VLSM also allows the recursive division of an organization's address

space so that it can be reassembled and aggregated to reduce the

amount of routing information at the top level. Conceptually, a network

is first divided into subnets, then some of the subnets are divided into

sub subnets, and some of the sub subnets are divided into sub subnets.

This allows the detailed structure of routing information for one subnet

group to be hidden from routers in another subnet group. 

11.0.0.0./8 11.1.0.0/16

11.2.0.0/16

11.3.0.0/16

11.252.0.0/16

11.253.0.0/16

11.254.0.0/16 11.1.1.0/24

11.1.2.0/24

11.1.253.0/24

11.1.254.0/24

11.253.32.0/19

11.253.64.0/19

11.253.160.0/19

11.253.192.0/19 11.1.253.32/27

11.1.253.64/27

11.1.253.160/27

11.1.253.192/27 

2 1