Dell S4048T, Configuration Manual, Page: 1129 / 1277

5 Configure a PIM-enabled external neighboring router as a rendezvous point (RP). For more information,
refer to Configuring a Static Rendezvous Point .
6 Configure the VLT VLAN routing metrics to prefer VLT VLAN interfaces over non-VLT VLAN interfaces.
For more information, refer to Classify Traffic .
7 Configure symmetrical Layer 2 and Layer 3 configurations on both VLT peers for any spanned VLAN.
Non-VLT ARP Sync
ARP entries (including ND entries) learned on other ports are synced with the VLT peer to support station
move scenarios.
NOTE: ARP entries learned on non-VLT, non-spanned VLANs are not synced with VLT peers.
RSTP Configuration
RSTP is supported in a VLT domain.
Before you configure VLT on peer switches, configure RSTP in the network. RSTP is required for initial loop
prevention during the VLT startup phase. You may also use RSTP for loop prevention in the network outside
of the VLT port channel. For information about how to configure RSTP,
Rapid Spanning Tree Protocol (RSTP) .
Run RSTP on both VLT peer switches. The primary VLT peer controls the RSTP states, such as forwarding and
blocking, on both the primary and secondary peers. Dell Networking recommends configuring the primary
VLT peer as the RSTP primary root device and configuring the secondary VLT peer as the RSTP secondary
root device.
BPDUs use the MAC address of the primary VLT peer as the RSTP bridge ID in the designated bridge ID field.
The primary VLT peer sends these BPDUs on VLT interfaces connected to access devices. The MAC address
for a VLT domain is automatically selected on the peer switches when you create the domain (refer to
Enabling VLT and Creating a VLT Domain ).
Configure both ends of the VLT interconnect trunk with identical RSTP configurations. When you enable VLT,
the
show spanning-tree rstp brief
command output displays VLT information (refer to
Verifying a VLT Configuration ).
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
Rapid Spanning Tree Protocol (RSTP) .
Disabling RSTP on one VLT peer may result in a VLT domain failure.
2 Enable RSTP on each peer switch.
Virtual Link Trunking (VLT) 1129