361
Configuring Optional Spanning-Tree Features
Information About Configuring the Optional Spanning-Tree Features
Figure 51
Root Guard in a Service-Provider Network
Enabling Root Guard
Root guard enabled on an interface applies to all the VLANs to which the interface belongs. Do not enable the root guard
on interfaces to be used by the UplinkFast feature. With UplinkFast, the backup interfaces (in the blocked state) replace
the root port in the case of a failure. However, if root guard is also enabled, all the backup interfaces used by the
UplinkFast feature are placed in the root-inconsistent state (blocked) and are prevented from reaching the forwarding
state.
Note:
You cannot enable both root guard and loop guard at the same time.
Loop Guard
You can use loop guard to prevent alternate or root ports from becoming designated ports because of a failure that leads
to a unidirectional link. This feature is most effective when it is enabled on the entire switched network. Loop guard
prevents alternate and root ports from becoming designated ports, and spanning tree does not send BPDUs on root or
alternate ports.
You can enable this feature by using the
spanning-tree loopguard default
global configuration command.
When the switch is operating in PVST+ or rapid-PVST+ mode, loop guard prevents alternate and root ports from
becoming designated ports, and spanning tree does not send BPDUs on root or alternate ports.
When the switch is operating in MST mode, BPDUs are not sent on nonboundary ports only if the interface is blocked by
loop guard in all MST instances. On a boundary port, loop guard blocks the interface in all MST instances.
Enabling Loop Guard
You can use loop guard to prevent alternate or root ports from becoming designated ports because of a failure that leads
to a unidirectional link. This feature is most effective when it is configured on the entire switched network. Loop guard
operates only on interfaces that are considered point-to-point by the spanning tree.
Note:
You cannot enable both loop guard and root guard at the same time.
101232
Desired
root switch
Customer network
Potential
spanning-tree root without
root guard enabled
Enable the root-guard feature
on these interfaces to prevent
switches in the customer
network from becoming
the root switch or being
in the path to the root.
Service-provider network
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 ...