PowerConnect B-Series FCX Configuration Guide
267
53-1002266-01
Configuring STP related features
8
FIGURE 50
802.1W Draft 3 RSTP failover to alternate root port
In this example, port 3/3 on Switch 3 has become unavailable. In standard STP (802.1D), if the
root port becomes unavailable, the Switch must go through the listening and learning stages on the
alternate port to reconverge with the spanning tree. Thus, port 3/4 must go through the listening
and learning states before entering the forwarding state and thus reconverging with the spanning
tree.
802.1W Draft 3 avoids the reconvergence delay by calculating an alternate root port, and
immediately failing over to the alternate port if the root port becomes unavailable. The alternate
port is in the blocking state as long as the root port is in the forwarding state, but moves
immediately to the active state if the root port becomes unavailable. Thus, using 802.1W Draft 3,
Switch 3 immediately fails over to port 3/4, without the delays caused by the listening and learning
states.
802.1W Draft 3 selects the port with the next-best cost to the root bridge. For example, on Switch
3, port 3/3 has the best cost to the root bridge and thus is selected by STP as the root port. Port
3/4 has the next-best cost to the root bridge, and thus is selected by 802.1W Draft 3 as the
alternate path to the root bridge.
X
The
a
rrow
s
how
s
the p
a
th
to the root bridge
Switch 1
Switch 2
Switch 4
Switch 3
Port 1/2
FWD
Port 2/2
FWD
Port 1/4
FWD
Port 2/4
FWD
Port 1/3
DISABLED
Root Bridge
Bridge priority = 2
Bridge priority = 6
Root port = 3/4
Bridge priority = 8
Root port = 4/4
Altern
a
te = 4/3
Bridge priority = 4
Root port = 2/2
Altern
a
te = 2/3, 2/4
Port 2/3
FWD
Port 4/3
BLK
Port 4/4
FWD
Port 3/4
FWD
Port 3/3
u
n
a
v
a
il
a
ble
Содержание PowerConnect B-FCXs
Страница 1: ...53 1002266 01 18 March 2011 PowerConnect B Series FCX Configuration Guide ...
Страница 136: ...94 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Viewing information about software licenses 4 ...
Страница 228: ...186 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 229: ...PowerConnect B Series FCX Configuration Guide 187 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 230: ...188 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 248: ...206 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IPv6 management commands 7 ...
Страница 346: ...304 PowerConnect B Series FCX Configuration Guide 53 1002266 01 802 1s Multiple Spanning Tree Protocol 8 ...
Страница 374: ...332 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Jumbo frame support 9 ...
Страница 424: ...382 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Virtual Switch Redundancy Protocol VSRP 10 ...
Страница 568: ...526 PowerConnect B Series FCX Configuration Guide 53 1002266 01 CLI examples 14 ...
Страница 588: ...546 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Sample application 15 ...
Страница 674: ...632 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Enabling or disabling layer 2 switching 19 ...
Страница 684: ...642 PowerConnect B Series FCX Configuration Guide 53 1002266 01 VLAN based mirroring 20 ...
Страница 724: ...682 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Reading CDP packets 23 ...
Страница 768: ...726 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing cached LLDP neighbor information 24 ...
Страница 930: ...888 PowerConnect B Series FCX Configuration Guide 53 1002266 01 26 ...
Страница 948: ...906 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Configuring MLD snooping 27 ...
Страница 962: ...920 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying CPU utilization statistics 28 ...
Страница 1022: ...980 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying OSPF information 29 ...
Страница 1142: ...1100 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing diagnostic buffers 30 ...
Страница 1258: ...1216 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Using Secure copy with SSH2 33 ...
Страница 1314: ...1272 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying port security information 35 ...
Страница 1348: ...1306 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Example configurations 36 ...
Страница 1406: ...1364 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IP source guard 39 ...
Страница 1422: ...1380 PowerConnect B Series FCX Configuration Guide 53 1002266 01 SNMP v3 Configuration examples 40 ...