357
Configuring Optional Spanning-Tree Features
Information About Configuring the Optional Spanning-Tree Features
Figure 46
UplinkFast Example Before Direct Link Failure
If Switch C detects a link failure on the currently active link L2 on the root port (a
direct
link failure), UplinkFast unblocks
the blocked interface on Switch C and transitions it to the forwarding state without going through the listening and
learning states, as shown in
. This change takes approximately 1 to 5 seconds.
Figure 47
UplinkFast Example After Direct Link Failure
Enabling UplinkFast for Use with Redundant Links
UplinkFast cannot be enabled on VLANs that have been configured with a switch priority. To enable UplinkFast on a VLAN
with switch priority configured, first restore the switch priority on the VLAN to the default value by using the
no
spanning-tree vlan
vlan-id
priority
global configuration command.
Note:
When you enable UplinkFast, it affects all VLANs on the switch. You cannot configure UplinkFast on an individual
VLAN.
You can configure the UplinkFast feature for rapid PVST+ or for the MSTP, but the feature remains disabled (inactive) until
you change the spanning-tree mode to PVST+.
When UplinkFast is enabled, the switch priority of all VLANs is set to 49152. If you change the path cost to a value less
than 3000 and you enable UplinkFast or UplinkFast is already enabled, the path cost of all interfaces and VLAN trunks is
increased by 3000 (if you change the path cost to 3000 or above, the path cost is not altered). The changes to the switch
priority and the path cost reduce the chance that a switch will become the root switch.
When UplinkFast is disabled, the switch priorities of all VLANs and path costs of all interfaces are set to default values if
you did not modify them from their defaults.
L1
L2
L3
Switch C
Switch A
(Root)
Switch B
Blocked port
43575
L1
L2
L3
Switch C
Switch A
(Root)
Switch B
UplinkFast transitions port
directly to forwarding state.
Link failure
43576
Summary of Contents for IE 4000
Page 12: ...8 Configuration Overview Default Settings After Initial Switch Configuration ...
Page 52: ...48 Configuring Interfaces Monitoring and Maintaining the Interfaces ...
Page 108: ...104 Configuring Switch Clusters Additional References ...
Page 128: ...124 Performing Switch Administration Additional References ...
Page 130: ...126 Configuring PTP ...
Page 140: ...136 Configuring CIP Additional References ...
Page 146: ...142 Configuring SDM Templates Configuration Examples for Configuring SDM Templates ...
Page 192: ...188 Configuring Switch Based Authentication Additional References ...
Page 244: ...240 Configuring IEEE 802 1x Port Based Authentication Additional References ...
Page 298: ...294 Configuring VLANs Additional References ...
Page 336: ...332 Configuring STP Additional References ...
Page 408: ...404 Configuring DHCP Additional References ...
Page 450: ...446 Configuring IGMP Snooping and MVR Additional References ...
Page 490: ...486 Configuring SPAN and RSPAN Additional References ...
Page 502: ...498 Configuring Layer 2 NAT ...
Page 770: ...766 Configuring IPv6 MLD Snooping Related Documents ...
Page 930: ...926 Configuring IP Unicast Routing Related Documents ...
Page 976: ...972 Configuring Cisco IOS IP SLAs Operations Additional References ...
Page 978: ...974 Dying Gasp ...
Page 990: ...986 Configuring Enhanced Object Tracking Monitoring Enhanced Object Tracking ...
Page 994: ...990 Configuring MODBUS TCP Displaying MODBUS TCP Information ...
Page 996: ...992 Ethernet CFM ...
Page 1066: ...1062 Using an SD Card SD Card Alarms ...