The IANA has allocated 233/8 for Multicast address space using BGP Autonomous System numbers. For instance, if CompanyA owns AS#5662, they would have 233.22.30.0/24 available to them for sourcing multicast groups across the Internet. How did we come up with that address range?

5662 written in binary is:

32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1
  0     0     0    1    0    1   1   0   0   0  0  1 1 1 1 0

Because 4096+1024+512+16+8+4+2=5662

The way GLOP addresses are created is by mapping the high order octet to the second octet of the address, and the low order octet to the third octet:

0 0 0 1 0 1 1 0 | 0 0 0 1 1 1 1 0

0 0 0 1 0 1 0 0 = 22
0 0 0 1 1 1 1 0 = 30

So we get 233.22.30.0/24 for our sole multicast use within AS 5662.

Another way to calculate the GLOP address is take the hexadecimal value of 5662, which is 161E. 16 hex equals 22 decimal. and 1E hex equals 30 decimal. Again, we get 233.22.30.0/24.

The lazy (smart?) way to calculate your GLOP address space is by entering it here and it will calculate if for you:  http://www.ogig.net/glop/

http://www.ietf.org/rfc/rfc3180.txt explains GLOP.
 
 

last update 11/2/2001 mmcbride