Administrator Guide

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
Configuring VLT
To configure virtual link trunking and create a VLT domain in which two switches are physically connected
and treated as a single port channel by access devices, you must configure the following settings on each VLT
peer device.
Prerequisites: Before you begin, make sure that both VLT peer switches are running the same Dell
Networking OS 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 Notessection.
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).
Virtual Link Trunking (VLT) 965