Configuring Spanning Trees As Hitless; Stp Loop Guard; Loop Guard Scenario - Dell Force10 C150 Configuration Manual

Configuring Spanning Trees as Hitless

Configuring Spanning Trees as Hitless
You can configure Spanning Tree (STP), Rapid Spanning Tree (RSTP), Multiple Spanning Tree (MSTP),
and Per-Vlan Spanning Tree (PVST+) to be hitless (all or none must be configured as hitless). When
configured as hitless, critical protocol state information is synchronized between RPMs so that RPM
failover is seamless, and no topology change is triggered.
Configure all Spanning Tree types to be hitless using the command
CONFIGURATION mode, as shown in
Figure 52-11. Configuring all Spanning Tree Types to be Hitless
FTOS(conf)#redundancy protocol xstp
FTOS#show running-config redundancy
!
redundancy protocol xstp
FTOS#

STP Loop Guard

STP Loop Guard

Loop Guard Scenario

The STP Loop Guard feature provides protection against Layer 2 forwarding loops (STP loops) caused by
a hardware failure, such as a cable failure or an interface fault. When a cable or interface fails, a
participating STP link may become unidirectional (STP requires links to be bidirectional) and an STP port
does not receive BPDUs. When an STP blocking port does not receive BPDUs, it transitions to a
forwarding state. This condition can create a loop in the network.
For example, in
normally transmits BPDUs to Switch C. The link between Switch C and Switch B is in a blocking state.
However, if there is a unidirectional link failure (STP topology 1 - lower left), Switch C does not receive
BPDUs from Switch B. When the
and transitions to forwarding state. A loop is created as both Switch A and Switch C transmit traffic to
Switch B.
Note that in
on Switch B becomes busy and does not forward BPDUs within the configured
result, the blocking port on Switch C transitions to a forwarding state, and both Switch A and Switch C
transmit traffic to Switch B (STP topology 2 - lower right).
1064 | Spanning Tree Protocol
is supported only on platforms:
Figure 52-12 (STP topology 1 - upper left), Switch A is the root switch and Switch B
max-age
Figure 52-12 (STP topology 2 - upper right), a loop can also be created if the forwarding port
is supported only on platforms:
Figure 52-11.
c e s
timer expires, the STP port on Switch C becomes unblocked
c e
redundancy protocol xstp
forward-delay
from
time. As a