Variable-Length Subnet Masks (VLSM)
A variable-length subnet mask (VLSM) is designed to allow more efficient use of IP address space by borrowing bits from the subnet mask and allocating them to host devices. To allow a greater number of devices to connect to the Internet and intranets, the standards body of various routing protocols designed an IP routing algorithm to cater to IP networks with a different subnet mask than the default used in classful networks.
Note
The following routing algorithms support VLSM: RIP Version 2, OSPF, IS-IS, EIGRP, and BGP4.
To demonstrate the use of VLSM, consider the example of connecting two Cisco routers through a wide-area link. Only two devices host systems are needed.
To use any IP address space effectively, ...
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