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:
•
https://www.cisco.com/en/US/i/templates/blank.gifThere 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.
source:
https://www.cisco.com/en/US/docs/ios.../1cfipadr.html