Reference Guide
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 Overview section as a sample VLT topology, the primary VLT switch sends BPDUs to an
access 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)
FTOS_VLTpeer1(conf)#protocol spanning-tree rstp
FTOS_VLTpeer1(conf-rstp)#no disable
FTOS_VLTpeer1(conf-rstp)#bridge-priority 4096
Configure RSTP on VLT Peers to Prevent Forwarding Loops (VLT Peer 2)
FTOS_VLTpeer2(conf)#protocol spanning-tree rstp
FTOS_VLTpeer2(conf-rstp)#no disable
FTOS_VLTpeer2(conf-rstp)#bridge-priority 0
Configuring VLT
To configure VLT, use the following procedure.
Prerequisites: Before you begin, make sure that both VLT peer switches are running the same FTOS version and are
configured for RSTP as described in RSTP Configuration. For VRRP operation, ensure that you configure VRRP groups
and L3 routing on each VLT peer as described in
VLT and VRRP interoperability
in the Configuration Notes section.
To configure VLT and create a VLT domain in which two S4820T switches are physically connected and treated as a
single port channel by access devices, configure the following settings on each VLT peer device.
1. Configure the VLT interconnect for the VLT domain. The primary and secondary switch roles in the VLT domain are
automatically assigned after you configure both sides of the VLTi.
NOTE: If you use a third-party ToR unit, to avoid potential problems if you reboot the VLT peers, Dell
recommends using static LAGs on the VLTi between VLT peers.
2. Enable VLT and create a VLT domain ID. VLT automatically selects a system MAC address.
3. Configure a backup link for the VLT domain.
4. (Optional) Manually reconfigure the default VLT settings, such as the MAC address and VLT primary/ secondary
roles.
5. Connect the peer switches in a VLT domain to an attached access device (switch or server).
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