OS10 Enterprise Edition User Guide Release 10.4.1.0

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Virtual Link Trunking

Virtual Link Trunking (VLT) is a Layer 2 (L2) aggregate protocol between end devices (servers) connected to different network devices. VLT reduces the role of Spanning Tree Protocols (STPs) by allowing link aggregation group (LAG) terminations on two separate distribution or core switches and supporting a loop-free topology.

  • Allows a single device to use a LAG across two upstream devices
  • Provides a loop-free topology
  • Eliminates STP-blocked ports
  • Optimizes the use of all available uplink bandwidth
  • Guarantees fast convergence if either a link or a device fails
  • Enhances optimized forwarding with Virtual Router Redundancy Protocol (VRRP)
  • Provides link-level resiliency
  • Assures high availability

VLT provides L2 multipathing, creating redundancy through increased bandwidth, enabling multiple parallel paths between nodes and load-balancing traffic where alternative paths exist.

vlt deployment

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

To ensure the same behavior on both sides of the VLT nodes, VRRP requires state information coordination. VLT configurations must be identical on both sides of a trunk. External switches or servers with LACP see the VLT switches as a single virtual switch.

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, RMON, AAA, ACL, DNS, FTP, SSH, syslog, 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 enable optimized L3 forwarding over VLT, use VRRP Active-Active mode. VRRP Active-Active mode enables each peer to locally forward L3, resulting in reduced traffic flow between peers over the VLTi.
Spanning-Tree Protocol
RSTP and RPVST+ are supported on VLT ports.
  • NOTE: 802.1x, DHCP snooping, MSTP, IGMP snooping, MLD snooping, ingress and egress QoS are not supported on VLT ports.

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