Supermicro SuperBlade SBM-GEM-X2C, Руководство пользователя

Страница: 75 / 334

21
Chapter 6: 1-Gb Ethernet Switch Firmware
root switch will set a Topology Change flag in its normal BPDUs. This flag is propagated
to all other switches to instruct them to rapidly age out their forwarding table entries.
Port Transition State
When a device is connected to an RTSP or STP enabled switch port for the first time, it
will not immediately start to forward data. Instead, it will go through a number of states
while it processes BPDUs and determines the network topology.
There are five port states in the legacy 802.1d STP: disabled , blocking , listening ,
learning and forwarding . The RSTP combines the disabled , blocking and listening states
used in 802.1d STP and creates a single state: Discarding . Table 6-7 lists the
comparison of port states between 802.1d STP and 802.1w RSTP.
RSTP Port Roles
RSTP will assign port roles for each port during the process receiving the BPDUs.
Based on its port role, a port can either send or receive BPDUs and forward or block
data traffic.
• Root – the port that provides the lowest cost path when the switch forwards packets
to the root switch.
• Designated – the port closest to the root switch and forwarding traffic toward the
root switch and sending BPDUs in a link segment. Each designated port is in a
forwarding state.
• Alternate – this port provides an alternate path to the root bridge. This path is
different than using the root port. The alternate port is in a blocking state.
• Backup – the port provides a backup/redundant path to a link segment to which
another switch port already connects. This is a special case when two or more ports
of the same switch are connected together.
• Disabled - Not a strictly part of RSTP, a network administrator can manually disable
a port.
To configure the R
APID
S
PANNING
T
REE
, click the S
PANNING
T
REE
folder on the left-hand
side bar. There are two portions to configure: RSTP S
WITCH
S
ETTINGS
and RSTP P
ORT
S
ETTINGS
, as shown in the R
APID
S
PANNING
T
REE
screen ( Figure 6-18 ).
Table 6-7. Comparison of Port States
State Displayed 802.1d STP 802.1w RSTP
Discarding Disabled Discarding
Discarding Blocking Discarding
Discarding Listening Discarding
Learning Learning Learning
Forwarding Forwarding Forwarding