Virtual Link Trunking

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Virtual Link Trunking (VLT) is a name that has been used for at least two proprietary network protocols. A link aggregation protocol developed by Force10 and an early VLAN tagging capability from 3Com.

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Force10

Virtual Link Trunking or VLT is a proprietary aggregation protocol developed by Force10 (now Dell Networking) and available in their datacenter-class or enterprise-class network switches. VLT is implemented in the latest firmware releases of legacy (FTOS) OS9 for their high-end switches like the S-, Z- and E-series 10/25,40 and 100 Gbit/s datacenter switches. [1] [2] [3] VLT is also implemented on the current OS10 Smart Fabric OS. Although VLT is a proprietary protocol from Dell Networking (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, also offers a similar protocol as MLAG

VLT is a layer-2 link aggregation 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. [2] 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. [3]

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'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. [3] An example configuration how it works can be found on the Blog Geslinux written by Grzegorz Witkowski [4]

3Com

Prior to supporting standardized IEEE 802.1Q tagging, 3Com used proprietary Virtual LAN Trunking (VLT). [5] 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.

See also

Related Research Articles

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 allows a network design to include backup links providing fault tolerance if an active link fails.

<span class="mw-page-title-main">VLAN</span> Network communications domain that is isolated at the data link layer

A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer. In this context, virtual refers to a physical object recreated and altered by additional logic, within the local area network. Basically, a VLAN behaves like a virtual switch or network link that can share the same physical structure with other VLANs while staying logically separate from them. Between network devices, VLANs work by applying tags to network frames and handling these tags in networking systems –creating the appearance and functionality of network traffic that is physically on a single network but acts as if it were split between separate networks. In this way, VLANs can keep network applications separate despite being connected to the same physical network, and without requiring multiple sets of cabling and networking devices to be deployed.

In telecommunications, trunking is a technology for providing network access to multiple clients simultaneously by sharing a set of circuits, carriers, channels, or frequencies, instead of providing individual circuits or channels for each client. This is reminiscent to the structure of a tree with one trunk and many branches. Trunking in telecommunication originated in telegraphy, and later in telephone systems where a trunk line is a communications channel between telephone exchanges.

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 procedures to be used by bridges and switches in handling such frames. The standard also contains provisions for a quality-of-service prioritization scheme commonly known as IEEE 802.1p and defines the Generic Attribute Registration Protocol.

VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that propagates the definition of Virtual Local Area Networks (VLAN) on the whole local area network. To do this, VTP carries VLAN information to all the switches in a VTP domain. VTP advertisements can be sent over 802.1Q, and ISL trunks. VTP is available on most of the Cisco Catalyst Family products. Using VTP, each Catalyst Family Switch advertises the following on its trunk ports:

<span class="mw-page-title-main">Link aggregation</span> Using multiple network connections in parallel to increase capacity and reliability

In computer networking, link aggregation is the combining of multiple network connections in parallel by any of several methods. Link aggregation increases total throughput beyond what a single connection could sustain, and provides redundancy where all but one of the physical links may fail without losing connectivity. A link aggregation group (LAG) is the combined collection of physical ports.

<span class="mw-page-title-main">EtherChannel</span> Computer networking link aggregation technology

EtherChannel is a port link aggregation technology or port-channel architecture used primarily on Cisco switches. It allows grouping of several physical Ethernet links to create one logical Ethernet link for the purpose of providing fault-tolerance and high-speed links between switches, routers and servers. An EtherChannel can be created from between two and eight active Fast, Gigabit or 10-Gigabit Ethernet ports, with an additional one to eight inactive (failover) ports which become active as the other active ports fail. EtherChannel is primarily used in the backbone network, but can also be used to connect end user machines.

Cisco Inter-Switch Link (ISL) is a Cisco proprietary link layer protocol that maintains VLAN information in Ethernet frames as traffic flows between switches and routers, or switches and switches. ISL is Cisco's VLAN encapsulation protocol and is supported only on some Cisco equipment over the Fast and Gigabit Ethernet links. It is offered as an alternative to the IEEE 802.1Q standard, a widely used VLAN tagging protocol, although the use of ISL for new sites is deprecated by Cisco.

The Multiple Spanning Tree Protocol (MSTP) and algorithm, provides both simple and full connectivity assigned to any given virtual LAN (VLAN) throughout a bridged local area network. MSTP uses bridge protocol data unit (BPDUs) to exchange information between spanning-tree compatible devices, to prevent loops in each Multiple Spanning Tree instance (MSTI) and in the common and internal spanning tree (CIST), by selecting active and blocked paths. This is done as well as in Spanning Tree Protocol (STP) without the need of manually enabling backup links and getting rid of switching loop danger.

<span class="mw-page-title-main">Router on a stick</span> Router that has a single connection to a network

A router on a stick, also known as a one-armed router, is a router that has a single physical or logical connection to a network. It is a method of inter-VLAN routing where one router is connected to a switch via a single cable. The router has physical connections to the broadcast domains where one or more VLANs require the need for routing between them.

The current portfolio of PowerConnect switches are now being offered as part of the Dell Networking brand: information on this page is an overview of all current and past PowerConnect switches as per August 2013, but any updates on current portfolio will be detailed on the Dell Networking page.

<span class="mw-page-title-main">Multi-link trunking</span> Network link aggregation technology

Multi-link trunking (MLT) is a link aggregation technology developed at Nortel in 1999. It allows grouping several physical Ethernet links into one logical Ethernet link to provide fault-tolerance and high-speed links between routers, switches, and servers.

A multi-chassis link aggregation group is a type of link aggregation group (LAG) with constituent ports that terminate on separate chassis, primarily for the purpose of providing redundancy in the event one of the chassis fails. The IEEE 802.1AX-2008 industry standard for link aggregation does not mention MC-LAG, but does not preclude it. Its implementation varies by vendor; notably, the protocol existing between the chassis is proprietary.

IEEE 802.1ad is an amendment to the IEEE 802.1Q-1998 networking standard which adds support for provider bridges. It was incorporated into the base 802.1Q standard in 2011. The technique specified by the standard is known informally as stacked VLANs or QinQ.

TRILL is a networking protocol for optimizing bandwidth and resilience in Ethernet networks, implemented by devices called TRILL switches. TRILL combines techniques from bridging and routing, and is the application of link-state routing to the VLAN-aware customer-bridging problem. Routing bridges (RBridges) are compatible with, and can incrementally replace, previous IEEE 802.1 customer bridges. TRILL Switches are also compatible with IPv4 and IPv6, routers and end systems. They are invisible to current IP routers, and like conventional routers, RBridges terminate the broadcast, unknown-unicast and multicast traffic of DIX Ethernet and the frames of IEEE 802.2 LLC including the bridge protocol data units of the Spanning Tree Protocol.

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 renamed to Dell Networking Operating System (DNOS) 9.x or above, while the legacy PowerConnect switches will use DNOS 6.x: see the separate article on DNOS.

Dell Networking is the name for the networking portfolio of Dell. In the first half of 2013, Dell started to rebrand their different existing networking product brands to Dell Networking. Dell Networking is the name for the networking equipment that was known as Dell PowerConnect, as well as the Force10 portfolio.

DNOS or Dell Networking Operating System is a network operating system running on switches from Dell Networking. It is derived from either the PowerConnect OS or Force10 OS/FTOS and will be made available for the 10G and faster Dell Networking S-series switches, the Z-series 40G core switches and DNOS6 is available for the N-series switches.

<span class="mw-page-title-main">Open vSwitch</span> Virtual network switch

Open vSwitch (OVS) is an open-source implementation of a distributed virtual multilayer switch. The main purpose of Open vSwitch is to provide a switching stack for hardware virtualization environments, while supporting multiple protocols and standards used in computer networks.

References

  1. ↑ Datacenterknowledge.com: F10's open-cloud networking, 27 April 2011. Visited: 26 June 2012
  2. 1 2 ITWorldcanada.com blog: F10 taking datacenters in zettabyte era, Jim Duffy, 26 April 2011. Visited: 26 June 2012
  3. 1 2 3 Inter NMS website: Playing Nice with Force10, 16 May 2012. Visited: 29 July 2012
  4. ↑ Geslinux blog Dell Force10 S4810 Virtual Link Trunking (VLT) Sample Configuration, 28 June 2012. Visited 2 July 2013
  5. ↑ "Connecting Common VLANs Between Switch Units". SuperStack II Switch 3000 TX 8 Port User Guide. June 1997. Document No. DUA1694-1AAA04.
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