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The following table describes the Class C equivalent of CIDR prefixes.
CIDR Prefix
Class C Equivalent
Host Addresses
/27
1/8 Class C
32 Hosts
/26
1/4 Class C
64 Hosts
/25
1/2 Class C
128 Hosts
/24
1 Class C
256 Hosts
/23
2 Class C
512 Hosts
/22
4 Class C
1,024 Hosts
/21
8 Class C
2,048 Hosts
/20
16 Class C
4,096 Hosts
/19
32 Class C
8,192 Hosts
/18
64 Class C
16,384 Hosts
/17
128 Class C
32,768 Hosts
/16
256 Class C OR 1 Class B
65,536 Hosts
/13
2,048 Class C
524,288 Hosts
An interface can have one primary IP address. To assign a primary IP address and a network mask to a network
interface, use the following command, starting in global configuration mode.
Command Purpose
Interface
interface name
Enters the interface configuration mode.
ip address
address
l
mask
Set a primary IP address for an interface.
5.1.1 Assign Multiple IP Addresses to Network Interfaces
The IC35516 software supports multiple IP addresses per interface. You can specify an unlimited number of
secondary addresses. Secondary IP addresses can be used in a variety of applications:
There might not be enough host addresses for a particular network segment
. S
uppose your sub-netting allows up to
254 hosts per logical subnet, but you need to have 300 host addresses on one physical subnet. Using secondary IP
addresses on the routers or access servers allows you to have two logical subnets using one physical subnet.
Many older networks were built using Level 2 bridges, and were not sub-netted. The use of secondary addresses can
aid in the transition to a sub-netted, router-based network. Routers on an older, bridged segment can easily be made
aware of multiple subnets are on that segment.
You can create a single network from subnets that are physically separated by another network by using a secondary
address. In these instances, the first network is layered on top of the second network. Note that a subnet cannot
appear on more than one active interface of the router at a time.
