Setup Guide

• 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.
NOTE: Reduce the multicast peer-routing-timeout value to 10 seconds to clear the (S,G) entry in mroute in primary
VLT peer. Also, the MLD leave packet must be sent after the unicast route convergence.
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).
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.
Virtual Link Trunking (VLT)
899