Table of Contents
Advertisement
Bridge ports and router
links
Root Bridge
Priorities and cost factors
Spanning tree topology
112
In bridging, "port" is used to describe each connection to the bridge. In the router,
"port" used to describe the physical LAN and WAN ports, and WAN and ports
can support more than one WAN link. For the purposes of describing bridging
correctly, the words "ports" and "links" are interchangeable when describing
bridge ports within the router.
During the Listening State, the bridge with the highest priority is determined.
This bridge is then defined as the "Root Bridge".
A priority is defined for each bridge and to each link of the bridge, the priority
for the bridge is defined by the
for a link, is defined by the
"cost factor" assigned to it which uses the Path Cost defined by the
parameter.
These parameters are used by the Spanning Tree Algorithm to determine the to-
pology of the bridged network.
The cost factor is used to calculate the distance from each link of a bridge to the
Root Bridge. On the basis of this, each link on a bridge is assigned one of the fol-
lowing states:
Root Port
"Root Port" is assigned to links that is closest to the Root Bridge. Only one link
on each bridge is assigned as the Root Port.
Designated Port
"Designated Port" is assigned to links that connect to bridges further away from
the Root Bridge than the bridge. The Root Bridge can only have Designated and
Blocking Ports.
Blocking
If any links are not assigned a Root Port or a Designated Port State, they are as-
signed a "Blocking" State. When a link is in the Blocking State, with the excep-
tion of Configuration BPDUs, packets are not accepted or transmitted by the link.
The link can be said to be in standby.
parameter and the priority
Bridge Priority
parameter. Each link also has a
Port Priority
WAN Bridging Services
Spanning Tree Algorithm
Path Cost
Advertisement
Table of Contents
