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The Length B value is the total byte count of the hex IP Addresses. In the example below, there are 2x IP hex addresses. Each IP
hex address is 4-bytes, therefore Length B is 8-bytes in total which equates to 08 in hex.
Length A includes Sub-option 1 (1-byte) and the Length B value (1-byte) plus the total of Length B (8-bytes). This makes the total
10-bytes which equates to 0a in hex.
Example
In the following example an additional IP address will be added to the existing DHCP option 125 hex code shown previously. It
will be a Satellite iPATH whose IP address is 10.0.30.1 which is on a different subnet.
Step 1: Convert IP Address 10.0.30.1 into hex, which is 0a001e01. Add it to the end of the hex code:
0000621f
..
01
..
0a001405
0a001406
0a001e01
Step 2: Calculate Length B. Since we now have 3x IP addresses and each hex address is 4-bytes, the total length is 12-bytes
which equates to 0c in hex:
0000621f
..
01
0c
0a001405
0a001406
0a001e01
Step 3: Calculate Length A. This is the total of Length B plus the byte count for Sub-option 1 and the Length B value. The Sub-
option 1 and Length B values are 1-byte each, the Length B total is 12-bytes. This makes the total of Length A to be 14-bytes
which equates to 0e in hex:
0000621f
0e
01
0c0a001405
0a001406
0a001e01
0000621f
0a
01
08
0a001405
0a001406
Length B
4 bytes
4 bytes
(Total 8 bytes)
0000621f
0a
01
08
0a001405
0a001406
Length A
4 bytes
4 bytes
(Total 10 bytes)
2 bytes