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. The lazy 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