Dell EMC SmartFabric OS10 User Guide Release 10.5.1

Virtual Link Trunking (VLT) is a Layer 2 aggregation protocol used between an end device such as a server and two or more connected network devices. VLT helps to aggregate ports terminating on multiple switches. OS10 currently supports VLT port channel terminations on two different switches.

VLT:

• Provides node-level redundancy by using the same port channel terminating on multiple upstream nodes.
• Provides a loop-free topology
• Eliminates STP-blocked ports
• Optimizes bandwidth utilization by using all available uplink bandwidth
• Guarantees fast convergence if either a link or device fails
• Enhances optimized forwarding with Virtual Router Redundancy Protocol (VRRP)
• Optimizes routing with VLT peer routing for Layer-3 VLANs
• Provides link-level resiliency
• Assures high availability

VLT presents a single logical L2 domain from the perspective of attached devices that have a virtual link trunk terminating on separate nodes in the VLT domain. The two VLT nodes are independent Layer2/ Layer3 (L2/L3) switches for devices in the upstream network. L2/L3 control plane protocols and system management features function normally in both the VLT nodes.

External switches or servers supporting LACP see the two VLT switches as a single virtual switch. Hence, VLT configurations must be identical on both the switches in the VLT domain.

VLT physical ports

802.1p, 802.1q, LLDP, flow control, port monitoring, and jumbo frames are supported on VLT physical ports.

System management protocols

All system management protocols are supported on VLT ports—SNMP, AAA, ACL, DNS, FTP, SSH, system log, NTP, RADIUS, SCP, and LLDP.

L3 VLAN connectivity

Enable L3 VLAN connectivity, VLANs assigned with an IP address, on VLT peers by configuring a VLAN interface for the same VLAN on both devices.

Optimized forwarding with VRRP

To ensure the same behavior on both sides of the VLT nodes, VRRP requires state information coordination. VRRP Active-Active mode optimizes L3 forwarding over VLT. By default, VRRP Active-Active mode is enabled on all the VLAN interfaces. VRRP Active-Active mode enables each peer to locally forward L3 packets, resulting in reduced traffic flow between peers over the VLTi link.

Spanning-Tree Protocol

VLT ports support RSTP, RPVST+, and MSTP.

Multicast

IGMP snooping and MLD snooping are supported on VLT ports.