Differences In Port Roles; Edge Port - Avaya 8600 Engineering

1.2 Differences in Port Roles

RSTP is an enhanced version of STP. These two protocols have almost the same set of parameters.
Table 1 lists the differences in port roles for STP and RSTP. STP supports 2 port roles while RSTP
supports four port roles. MSTP adds an extra role for MSTI instances only.
Port Role STP
Root Yes
Designated Yes
Backup No
Alternate No
Master No

1.3 Edge Port

Edge port is a new parameter that is supported by RSTP/MSTP. When a port is connected to a non-
switch device such as a PC or a workstation, it must be configured as an Edge port or else it will take 30
seconds to transition into a Forwarding state. An active Edge port is similar to the STP FastStart feature
in that the port can go directly into Forwarding state without any delay. An Edge port always generates
BPDUs but immediately becomes a non Edge port if it receives a BPDU.
July 2010
Table 1 Difference in Port Roles for STP and RSTP
RSTP MSTP
Yes Yes
Yes Yes
Yes Yes
Yes Yes
No Yes
RSTP/MSTP Technical Configuration Guide
Description
On a non-root bridge, this port is receiving BPDUs
with the lowest root path cost, i.e. this port is the
best path to reach the Root bridge in the
STP/RSTP domain or in the CIST or MSTI
instance for MSTP. The Root port is always in
Forwarding state.
The bridge owning this port (Designated Bridge)
has the lowest root path cost towards the Root
bridge for this segment and, in case of a tie, best
Bridge priority and Port priority. This port will
generate BPDUs every 2 seconds on the segment
and will transition in Forwarding state.
A bridge port that is not Root port or Designated
port is a Backup port if the same bridge is already
the Designated Bridge for the same segment (via
a different port). A Backup port is always in
Discarding state.
A bridge port that is not Root port or Designated
port or Backup port is an Alternate port. An
Alternate port is always in Discarding state.
On an MSTP MSTI instance only, this port is on
an MST region boundary and has the lowest root
path cost towards the CIST Root bridge (CIST
Regional Root)
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