There can be situations in a campus where an Ethernet domain was originally configured for 30 hosts using a /27 mask. However, if we need to add more hosts to the same network, we ideally have to change the IP address subnet and use a bigger subnet say a /26 that will allow a larger number of hosts. This will mean readdressing all hosts on the subnet.
A workaround for this is to use secondary IP addresses on interfaces. This will allow an interface to have two IP addresses, and hence act like the default gateway for two subnets without having the need to readdress the hosts on the network: