2. SUBNETTING
IT’S A PROCESS OF DIVIDING A SINGLE NETWORK INTO
MULTIPLE NETWORKS.
THIS IS DONE BY CONVERTING HOST’S BITS INTO NETWORK’S
BITS (i.e. Converting 0’s into 1’s).
IT IS ALSO CALLED FLSM.
IT CAN BE DONE IN THREE WAYS:
Requirement of network.
Requirement of hosts.
Cisco / notation.
A SUBNET MASK IS ALWAYS A COMBINATION OF CONTIGUOUS
1’s AND 0’s. VALID SUBNET MASKS IN EACH OCTET ARE: 0, 128, 192,
224, 240, 248, 252, 254, 255.
4. VLSM
A VLSM IS A MEANS OF ALLOCATING IP ADDRESSING
RESOURCES TO SUBNETS ACCORDING TO THEIR
INDIVIDUAL NEED RATHER THAN SOME GENERAL
NETWORK WIDE RULE.
VLSM ALLOWS AN ORGANISATION TO USE MORE
THAN ONE SUBNET MASK WITHIN THE SAME
NWTWORK ADDRESS SPACE. IT IS REFERRED TO AS
“SUBNETTING A SUBNET” AND CAN BE USED TO
MAXIMIZE ADDRESSING EFFICIENCY.
LARGER SUBNETS ARE CREATED FOR ADDRESSING
LAN’s AND SMALL SUBNETS FOR WAN LINKS (e.g. a 30
bit subnet mask is used to create subnet with only two
hosts).
5. SUBNETTING vs VLSM
SUBNETTING ALLOWS YOU TO DIVIDE BIG
NETWORK INTO SMALLER EQUAL SIZED SLICES.
VLSM ALLOWS YOU TO DIVIDE BIG NETWORK
INTO SMALLER, DIFFERENT-SIZED SLICES. THIS
ALLOWS YOU TO MAKE MAXIMUM USE OF THE
VALUABLE ADDRESS SPACE.