bridge priority and multiples of 4096...

excellent question posted to cln...  are you on the cln?

why is the bridge priority determined in multiples of 4096?

below is an excellent explanation from http://communitystring.com/2008/07/why-the-stp-bridge-priority-must-be-a-multiple-of-4096/

Therefore to prevent the overuse of the MAC addresses they turned the 2 bytes which was used in the priority field of the Bridge ID into a 4 bit priority and used the remaining 12 bits for the vlan, the extra information which is used to carry the VLAN number is called the Extended System ID, and this process is sometimes called MAC address reduction as it reduces the number of reserved MAC addresses needed. The 12 bits of extra VLAN information allows support for 4096 VLANs, so there is full support for extended range VLANs. Therefore because of the use of the Extended System ID in the Bridge ID, there is only the first 4 bits of the original 2 byte number to be used for the bridge priority so it only allows multiplies of 4096.

what is 2^12? 

also here is the root of this site... definitely worth a look...

http://communitystring.com


go there now...