ZyXEL Communications ES-2048 - Manual (Page 57)

ES-2000 Series Switch Support Notes
All contents copyright (c) 2006 ZyXEL Communications Corporation.
57
2. The bridge ID includes two parts, bridge priority (2 bytes) and
bridge MAC address (6 bytes). The 802.1d default bridge priority is
32768. For example, a switch with default priority 32768 (8000 hex),
MAC address is 00:A0:C5:12:34:56, its bridge ID is
8000:00A0:C512:3456.
3. On the root bridge, all its ports are designated ports. Designated
ports are always in the forwarding state. While in forwarding
state, a port can receive and send traffic.
2. Select a root port for the non-root bridge
For the non-root switch/bridge, there will be one root port. The root port is the
port through which this non-root switch / bridge communicates with the root
bridge (the "leaf" side of the "tree").
1. The root port is the port on the non-root bridge with the lowest path
cost to the root bridge. The root port is normally in forwarding
state.
2. Path cost is the total cost of transmitting a frame on to a LAN
through that port to bridge root. It is assigned according to the
bandwidth of the link. The slower the media, the higher the cost.
Some of the path costs specified in the IEEE 802.1d specification
are listed below.
Link Speed
Recommended
Cost
Recommended
Cost Range
4Mbps 250 100 to 1000
10Mbps 100 50 to 600
16Mbps 62 40 to 400
100Mbps 19 10 to 60
1Gbps 4 3 to 10
10Gbps 2 1 to 5
3. When multiple ports have the same path cost to root bridge, the
port with lowest port priority is selected as root port.
3. Select a designated port on each segment