Qtech QSW-2800v2 [187/230] In cist priority vector is composed of the total root outer root path cost domain

Qtech QSW-2800v2 [187/230] In cist priority vector is composed of the total root outer root path cost domain
Chapter8 Reliability Configuration
8-5
Table 8-1 Interface Role Selection Principle
Port Role
Choosing Principle
Root Interface
Port priority vector is better than the designated priority vector of
the port. And the root priority vector of device derives from the root
path priority vector of the port.
Designated Interface
The designated priority vector of port is better than the port priority
vector.
Master Interface
The role of domain boundary root port in MSTI instance is the
Master port.
Alternate Interface
Port priority is better than the designated priority vector of the port.
But the root priority vector of device does not derive from the root path
priority vector of the port.
Backup Interface
Port priority is better than the designated priority vector of the port.
But the designated ID of port priority vector is the bridge ID of local
device.
3. Priority Vector Calculation
The MSTP role of all bridges is computed according to the carrying information in
the message. The most important information carried in the message is the
priority vector of the spanning tree. We will introduce the CIST priority vector and
MSTI priority vector calculation method as follow.
a) CIST Priority Vector Calculation
In CIST, priority vector is composed of the total root, outer root path cost, domain
root, inner root path cost, designated bridge ID, designated port ID and the ID of
port receiving BPDU message.
In order to facilitate the subsequent description, we make the following
assumptions.
In the initial condition, the information carried in the message sent out by the
PB port of the bridge B is as follow. The total root is RB. The outer root path
cost is ERCB. The domain root is RRB. The inner root path cost is IRCB. The
designated bridge ID is B. The designated port is B. The designated port ID
is PB. The ID of port receiving BPDU message is PB.
The information carried in the message which is received by PB port of
bridge B from the PD port of bridge D is as follow. The total root is RD. The

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