the difference between system priority and bridge ID?

[Cossak Yu]

Hi,

I am reading the CCNP self Study BCMSN Official Exam Certificate Guide Fourth Edition. There is a System priority in the LACP set up. That is 2 bytes for priority value followed by a 6 byte MAC address. I am wondering what is the difference between system priority and the bridge ID related to STP. Bridge ID also consists of 2 bytes bridge priority and 6 bytes MAC address. if they are the same, why they are given two different names? Could any one give me a help on this?

thanks,

Cossak

[Viral Bhutta]

LACP system Priority is the combination of the LACP system priority value and the MAC address of the switch.

You can configure it using lacp system-priority priority_value

LACP uses the system priority with the switch MAC address to form the system ID and also during negotiation with other systems.

http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/channel.html#wp1033345

Each VLAN on each network device has a unique 64-bit bridge ID consisting of a bridge priority value, an extended system ID, and an STP MAC address allocation.

Configuring Bridge ID Priority

spanning-tree vlan vlan_id priority bridge_priority

http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/spantree.html#wp1096536

In short, both values are different.Both are used for different purpose.

Hope this helps.