D-Link xStack DGS-3610 Series Configuration Manual page 177

DGS-3610 Series Configuration Guide
17.1.1.3 Bridge ID
In accordance with the prescription of the IEEE 802.1W standard, each bridge should
present unique Bridge ID, which will be taken as the standard to select the Root Bridge in the
algorithm of the spanning tree. The Bridge ID consists of 8 bytes, where, the latter 6 bytes is
the mac address of this bridge, while the first 2 bytes is shown as the table below. Of which,
the first 4 bits denote the priority, while the last 8 bits denotes the System ID for the use of
subsequent extending protocol.. This value is 0 in the RSTP, so the priority of the bridge
should be configured as the multiple of 4096.
Bits
Value
17.1.1.4 Spanning-Tree Timers
The following description has an effect on three timers of the performance for the whole
spanning-tree.
Hello timer: The time interval for forwarding the BUDU packets periodically.

Forward-Delay timer: The time interval for the change of the port status. The time

interval when the port switches to the learning from the listening, or to the forwarding
from the learning if the RSTP protocol runs in the compatible STP protocol mode.
Max-Age timer: The longest time for the BPDU packets. Once it is timeout, the packets

will be discarded.
17.1.1.5 Port Roles and Port States
Each port will play a Port Role in the network and be used to represent different acts in the
network topology.
Root port: The port that provides the shortest path to the Root Bridge.

Designated port: The port by which each LAN is connected to the root bridge.

Alternate port: The alternate port of the root port which will change into the root port

once the root port fails.
Backup port: The backup port of the Designated port. If two ports are connected to one

LAN for the bridge, the port with higher priority is the Designated port, while that with
lower priority is the Backup port.
Disable port: The port that is not in the active status. Namely, the port whose operation

state is down is assigned to this role.
The roles of various ports are shown in following Figure 17-1, Figure 17-2 and Figure
17-3 :
Priority value
16 15 14 13
32768 16384 8192 4096
System ID
12 11 10 9
2048 1024 512 256 128 64 32 16 8 4
Chapter 17 MSTP Configuration
8 7 6 5 4 3 2 1
2 1
17-3