Setup Guide

Important Points to Remember
● You can only use one spanned VLAN from a PIM-enabled VLT node to an external neighboring PIM router.
● If you connect multiple spanned VLANs to a PIM neighbor, or if both spanned and non-spanned VLANs can access the PIM
neighbor, ECMP can cause the PIM protocol running on each VLT peer node to choose a different VLAN or IP route to reach
the PIM neighbor. This can result in issues with multicast route syncing between peers.
● Both VLT peers require symmetric Layer 2 and Layer 3 configurations on both VLT peers for any spanned VLAN.
● For optimal performance, configure the VLT VLAN routing metrics to prefer VLT VLAN interfaces over non-VLT VLAN
interfaces.
● When using factory default settings on a new switch deployed as a VLT node, packet loss may occur due to the requirement
that all ports must be open.
● ECMP is not compatible on VLT nodes using VLT multicast. You must use a single VLAN.
Configuring VLT Multicast
To enable and configure VLT multicast, follow these steps.
1. Enable VLT on a switch, then configure a VLT domain and enter VLT-domain configuration mode.
CONFIGURATION mode
vlt domain domain-id
2. Enable peer-routing.
VLT DOMAIN mode
peer-routing
3. Configure the multicast peer-routing timeout.
VLT DOMAIN mode
multicast peer-routing—timeout value
value: Specify a value (in seconds) from 1 to 1200.
4. Configure a PIM-SM compatible VLT node as a designated router (DR). For more information, refer to Configuring a
Designated Router.
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 EMC 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).
904
Virtual Link Trunking (VLT)