Reference Guide

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. The primary VLT switch
process BPDUs generated by an RSTP-enabled access device. 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
Configuring VLT
To configure VLT, use the following procedure.
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 Notes section.
To configure virtual link trunking and create a VLT domain in which two S5000 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, Dell Networking recommends using static LAGs on the
VLTi between VLT peers to avoid potential problems if you reboot the 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).
1006
Virtual Link Trunking (VLT)