Figure 136 Stp Root Ports And Designated Ports; Table 99 Rstp And Stp Port States - ZyXEL Communications MSC1000G User Manual

MSC1000G User's Guide

Figure 136 STP Root Ports and Designated Ports

RSTP-aware devices exchange Bridge Protocol Data Units (BPDUs) periodically. When the
bridged LAN topology changes, a new spanning tree is constructed.
In RSTP, the devices send BPDUs every Hello Time. If an RSTP-aware device does not get a
Hello BPDU after three Hello Times pass (or the Max Age), the device assumes that the link to
the neighboring bridge is down. This device then initiates negotiations with other devices to
reconfigure the network to re-establish a valid network topology.
In STP, once a stable network topology has been established, all devices listen for Hello
BPDUs transmitted from the root bridge. If an STP-aware device does not get a Hello BPDU
after a predefined interval (Max Age), the device assumes that the link to the root bridge is
down. This device then initiates negotiations with other devices to reconfigure the network to
re-establish a valid network topology.
RSTP assigns three port states to eliminate packet looping while STP assigns five (see
following table). A device port is not allowed to go directly from blocking state to forwarding
state so as to eliminate transient loops.

Table 99 RSTP and STP Port States

RSTP PORT
STATE
Discarding
Discarding
Discarding
Learning
Forwarding
222
STP PORT
DESCRIPTION
STATE
Disabled STP is disabled (default).
Blocking Only configuration and management BPDUs are received and
processed.
Listening All BPDUs are received and processed.
Learning All BPDUs are received and processed. Information frames are
submitted to the learning process but not forwarded.
Forwarding All BPDUs are received and processed. All information frames are
received and forwarded.
Chapter 13 Switch Screens