HP-UX LAN Administrator's Guide (Feburary 2007)

DRAFT COPY Network Addressing
Variable-Length Subnet Addressing
Chapter 7 119
In the next example. the entire host field has been allocated. As a result, only the subnet field
can grow.
Figure 7-10 Entire Host Field Allocated
To alleviate this restrictive situation, when you use the variable-length subnetting approach,
you can, alternatively, assign subnet numbers from the left of the subnet field and work right.
This is implemented using mirror-image counting. In the mirror image approach, the bits for
subnet numbers are assigned left to right instead of right to left (normal situation). This
would result in the following format:
Table 7-7 Mirror Image Counting
Traditional
Approach
Mirror
Image
Approach
01 10
10 01
011 110
100 001
101 101
0s 1s & 0s
1s & 0s
subnet field host field
subnets can
grow here