Preventing Forwarding Loops In A Vlt Domain; Sample Rstp Configuration - Dell Z9500 Configuration Manual

Preventing Forwarding Loops in a VLT Domain

During the bootup of VLT peer switches, a forwarding loop may occur until the VLT configurations are applied on each switch
and the primary/secondary roles are determined.
To prevent the interfaces in the VLT interconnect trunk and RSTP-enabled VLT ports from entering a Forwarding state and
creating a traffic loop in a VLT domain, take the following steps.
1 Configure RSTP in the core network and on each peer switch as described in
Disabling RSTP on one VLT peer may result in a VLT domain failure.
2 Enable RSTP on each peer switch.
PROTOCOL SPANNING TREE RSTP mode
no disable
3 Configure each peer switch with a unique bridge priority.
PROTOCOL SPANNING TREE RSTP mode
bridge-priority

Sample RSTP Configuration

The following is a sample of an RSTP configuration.
Using the example shown in the
device (switch or server) with its own RSTP bridge ID. BPDUs generated by an RSTP-enabled access device are only processed
by the primary VLT switch. The secondary VLT switch tunnels the BPDUs that it receives to the primary VLT switch over the VLT
interconnect. Only the primary VLT switch determines the RSTP roles and states on VLT ports and ensures that the VLT
interconnect link is never blocked.
In the case of a primary VLT switch failure, the secondary switch starts sending BPDUs with its own bridge ID and inherits all the
port states from the last synchronization with the primary switch. An access device never detects the change in primary/
secondary roles and does not see it as a topology change.
The following examples show the RSTP configuration that you must perform on each peer switch to prevent forwarding loops.
Configure RSTP on VLT Peers to Prevent Forwarding Loops (VLT Peer
1)
Dell_VLTpeer1(conf)#protocol spanning-tree rstp
Dell_VLTpeer1(conf-rstp)#no disable
Dell_VLTpeer1(conf-rstp)#bridge-priority 4096
Configure RSTP on VLT Peers to Prevent Forwarding Loops (VLT Peer
2)
Dell_VLTpeer2(conf)#protocol spanning-tree rstp
Dell_VLTpeer2(conf-rstp)#no disable
Dell_VLTpeer2(conf-rstp)#bridge-priority 0
Overview section as a sample VLT topology, the primary VLT switch sends BPDUs to an access
Rapid Spanning Tree Protocol
Virtual Link Trunking (VLT)
(RSTP).
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