Reference Guide

1002 | Virtual Link Trunking (VLT)
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Sample RSTP Configuration
Using Figure 53-361 as a sample VLT topology, the primary VLT switch will send 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 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 figures show an example of the RSTP configuration that you must perform on each peer
switch to prevent forwarding loops.
Figure 53-362. Configuring RSTP on VLT Peers to Prevent Forwarding Loops (VLT Peer 1)
Figure 53-363. Configuring RSTP on VLT Peers to Prevent Forwarding Loops (VLT Peer 2)
VLT Configuration 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 VRRP groups and L3 routing on each VLT peer are configured as described in VLT and VRRP
interoperability:.
To configure virtual link trunking and create a VLT domain in which two S4810 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:
1. Configure the VLT interconnect for the VLT domain. The primary and secondary switch roles in the
VLT domain are automatically assigned after both sides of the VLTi are configured.
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 default VLT settings, such as MAC address and VLT primary/
secondary roles.
Note: If a third-party ToR unit is used, Dell Force10 recommends using static LAGs on the VLTi between
VLT peers to avoid potential problems if the VLT peers are rebooted.
FTOS_VLTpeer1(conf)#protocol spanning-tree rstp
FTOS_VLTpeer1(conf-rstp)#no disable
FTOS_VLTpeer1(conf-rstp)#bridge-priority 4096
FTOS_VLTpeer2(conf)#protocol spanning-tree rstp
FTOS_VLTpeer2(conf-rstp)#no disable
FTOS_VLTpeer2(conf-rstp)#bridge-priority 0