Supernet Addressing And Cidr - Avaya 8800 Configuration Manual

Routing fundamentals
Number
of bits
2
3
4
5
6
7
8
9
10
11
12
13
14
1
2
3
4
5
6
With variable-length subnet masking (VLSM), you can divide your intranet into pieces that
match your requirements. Routing is based on the longest subnet mask or network that
matches. RIPv2 and OSPF both support VLSM.

Supernet addressing and CIDR

A supernet, or classless interdomain routing (CIDR) address, is a group of networks identified
by contiguous network addresses. IP service providers can assign customers blocks of
contiguous addresses to define supernets as needed. Using supernetting, you can address
an entire block of class C addresses and avoid using large routing tables to track the
addresses.
Each supernet has a unique supernet address that consists of the upper bits shared by all
addresses in the contiguous block. For example, consider the class C addresses shown in the
following figure. By adding the mask 255.255.128.0 to IP address 192.32.128.0, you aggregate
14 Configuration — OSPF and RIP
Subnet mask
255.255.192.0
255.255.224.0
255.255.240.0
255.255.248.0
255.255.252.0
255.255.254.0
255.255.255.0
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
Number of subnets
(recommended)
2
6
14
30
62
126
254
510
1 022
2 046
4 094
8 190
16 382
Class C
0
2
6
14
30
62
Number of hosts for
each subnet
16 382
8 190
4 094
2 046
1 022
510
254
126
62
30
14
6
2
126
62
30
14
6
2
June 2011