Virtual Link Trunking (VLT) is a name that has been used for at least two proprietary network protocols. A

link aggregation In computer networking, link aggregation is the combining ( aggregating) of multiple network connections in parallel by any of several methods, in order to increase throughput beyond what a single connection could sustain, to provide redundan ...

protocol developed by

Force10 Dell Force10 (formerly nCore Networks, Force10 Networks), was a United States company that developed and marketed 10 Gigabit and 40 Gigabit Ethernet switches for computer networking to corporate, educational, and governmental customers. It had ...

and an early

VLAN tagging IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying proce ...

capability from

3Com 3Com Corporation was an American digital electronics manufacturer best known for its computer network products. The company was co-founded in 1979 by Robert Metcalfe, Howard Charney and others. Bill Krause joined as President in 1981. Metcalfe e ...

Force10

Virtual Link Trunking or VLT is a proprietary

aggregation Aggregation may refer to: Business and economics * Aggregation problem (economics) * Purchasing aggregation, the joining of multiple purchasers in a group purchasing organization to increase their buying power * Community Choice Aggregation, the ...

protocol developed by

(now

Dell Networking Dell Networking is the new name for the networking portfolio of Dell. In the first half of 2013, Dell started to re-brand their different existing networking product brands to Dell Networking. Dell Networking will be the new name for the networkin ...

) and available in their datacenter-class or enterprise-class

network switch A network switch (also called switching hub, bridging hub, and, by the IEEE, MAC bridge) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. A netw ...

es. VLT is implemented in the latest firmware releases of legacy (

FTOS FTOS or Force10 Operating System is the firmware family used on Force10 Ethernet switches. It has a similar functionality as Cisco's NX-OS or Juniper's Junos. FTOS 10 is running on Debian. As part of a re-branding strategy of Dell FTOS will be re ...

) OS9 for their high-end switches like the S-, Z- and E-series 10/25,40 and 100 Gbit/s datacenter switches.Datacenterknowledge.com
F10's open-cloud networking
27 April 2011. Visited: 26 June 2012ITWorldcanada.com blog
F10 taking datacenters in zettabyte era
Jim Duffy, 26 April 2011. Visited: 26 June 2012Inter NMS website
Playing Nice with Force10
16 May 2012. Visited: 29 July 2012 VLT is also implemented on the current OS10 Smart Fabric OS. Although VLT is a proprietary protocol from

(formerly Force10) other vendors offer similar features to allow users to set up an aggregated link towards two (logical) different switches, where a standard aggregated link can only terminate on a single logical switch (thus either a single physical switch or on different members in a stacked switch setup) like Cisco vpc or MLAG. The latest Dell supported OS for their ONIE based PowerSwitch devices,

SONiC Sonic or Sonics may refer to: Companies *Sonic Drive-In, an American drive-in fast-food restaurant chain * Sonic (ISP), an Internet provider and CLEC, serving more than 100 California communities * Sonic Foundry, a computer software company wh ...

, also offers a similar protocol as MLAG VLT is a layer-2

protocol between end-devices (servers) connected to (different) access-switches, offering these servers a redundant, load-balancing connection to the core-network in a loop-free environment, eliminating the requirement for the use of a spanning-tree protocol. Where existing link aggregation protocols like (static) LAG (IEEE 802.3ad) or LACP (IEEE 802.1ax) require the different (physical) links to be connected to the same (logical) switch (such as stacked switches), the VLT, for example, allows link connectivity between a server and the network via two different switches. Instead of using VLT between end-devices like servers it can also be used for uplinks between (access/distribution) switches and the core switches. A major complication of existing link aggregation or bonding technologies is that all members interfaces of such a team/group need to terminate on one single logical switch. Beside increasing bandwidth another reason for link aggregation is redundancy. To make it possible to connect a LAG to different physical switches is to combine more than one physical switch into one logical switch using ''switch stacking'' techniques where the different physical boxes are seen as one logical switch for management and (spanning-tree) topology. The switches running in a stacked configuration always have to run the same firmware, which means that in case of a firmware upgrade the network manager has to implement the new firmware on all stack-members at the same time, resulting in an outage of the entire stack. The alternative is to have different logical switches, but then one of the used links will have to be blocked to ensure a loop-free topology (which can partially be overcome by using Multiple Spanning Tree or

Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational corporation, multinational digital communications technology conglomerate (company), conglomerate corporation headquartered in San Jose, California. Cisco develo ...

's proprietary ''per VLAN spanning tree''. Spanning Tree Protocol is relatively slow in convergence, which can result in periods that traffic can't be forwarded over the network - and thus leads to outages of the applications. VLT should address all these issues, making it possible to create a loop free redundant network topology without using the Spanning Tree Protocol. An example configuration how it works can be found on the Blog Geslinux written by Grzegorz Witkowski

3Com

Prior to supporting standardized

IEEE 802.1Q IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying proc ...

tagging,

used proprietary ''Virtual LAN Trunking'' (VLT).{{Cite book, title=SuperStack II Switch 3000 TX 8 Port User Guide , date=June 1997 , chapter=Connecting Common VLANs Between Switch Units , id=Document No. DUA1694-1AAA04 3Com VLT supported VLAN IDs 1–16 with 15 being reserved for Autoselect VLAN Mode (where a VLAN server decides port membership) and 16 reserved for

Spanning Tree Protocol The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them. Spanning tree also ...

References

Network protocols Link protocols Network topology Spanning tree Fault-tolerant computer systems Ethernet standards

Force10

3Com

See also

References