Secondary addressing

Apr 30, 2012 16:56

Assigning Multiple IP Addresses to Network Interfaces

Cisco IOS 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 situations. The following are the most common applications:


There might not be enough host addresses for a particular network segment. For example, suppose your subnetting allows up to 254 hosts per logical subnet, but on one physical subnet you must have 300 host addresses. 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 subnetted. The judicious use of secondary addresses can aid in the transition to a subnetted, router-based network. Routers on an older, bridged segment can easily be made aware that many subnets are on that segment.


Two subnets of a single network might otherwise be separated by another network. 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 extended, or 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.



Note
If any router on a network segment uses a secondary address, all other routers on that same segment must also use a secondary address from the same network or subnet.

To assign multiple IP addresses to network interfaces, use the following command in interface configuration mode:

Command

Purpose

Router(config-if)# ip address ip-address mask secondary

Assigns multiple IP addresses to network interfaces.



It works but it's not a really good design to do this.
Usually - with one interface.

network, ccna

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