Installing and Administering LAN/9000 Software

158 Chapter6
Network Addressing
Variable-Length Subnet Addressing
Notice that these additions caused A to change its leftmost g-bit into a
subnet-bit (“s” bit). With the addition of subnet address 101 for subnet
E, the old subnet address 10 of subnet A must be changed to 100 so that
the proper number of bits are used to make the subnet numbers unique.
Table 6-10 shows the results of removing subnet E.
Notice that with this change, subnet A gains back one growth bit (“g” bit)
as its old subnet address of 10 is now unique again.
Example of Subnets with Variable-Length Subnet Masks
The following example shows four subnetworks within the 192.6.12
Table 6-9 Subnets with Subnet Mask (B) Modified
Subnet
Host Address
(Bits)
Subnet Mask (Bits)
A 100g gghh 1111 1000
B 01hh hhhh 1100 0000
C 110g ghhh 1111 1000
D 001g ghhh 1111 1000
E 101g ghhh 1111 1000
F 1110 ghhh 1111 1000
Table 6-10 Subnets with Subnet E Removed
Subnet
Host Address
(Bits)
Subnet Mask (Bits)
A 10gg gghh 1111 1100
B 01hh hhhh 1100 0000
C 110g ghhh 1111 1000
D 001g ghhh 1111 1000
F 1110 ghhh 1111 1000