Multi-link trunking

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Nortel Multi-Link Trunking
Multi-link trunking example.jpg
MLT between ERS 5530 switch and an ERS 8600 switch

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. [1]

Contents

MLT allows the use of several links (from 2 up to 8) and combines them to create a single fault-tolerant link with increased bandwidth. This produces server-to-switch or switch-to-switch connections that are up to 8 times faster. Prior to MLT and other aggregation techniques, parallel links were underutilized due to Spanning Tree Protocol’s loop protection.

Fault-tolerant design is an important aspect of Multi-Link Trunking technology. Should any one or more than one link fail, the MLT technology will automatically redistribute traffic across the remaining links. This automatic redistribution is accomplished in less than half a second (typically less than 100 millisecond [2] ) so no outage is noticed by end users. This high speed recovery is required by many critical networks where outages can cause loss of life or very large monetary losses in critical networks. Combining MLT technology with Distributed Split Multi-Link Trunking (DSMLT), Split multi-link trunking (SMLT), and R-SMLT technologies create networks that support the most critical applications.

A general limitation of standard MLT is that all the physical ports in the link aggregation group must reside on the same switch. SMLT, DSMLT and R-SMLT technologies removes this limitation by allowing the physical ports to be split between two switches.

Split Multi-Link Trunking
IST and SMLT.JPG
SMLT mesh with nine 1Gig paths (all connections active and load balancing traffic) 9 Gbit/s full duplex mesh providing 18 Gbit/s of bandwidth between core switches.

Split multi-link trunking (SMLT) is a Layer-2 link aggregation technology in computer networking originally developed by Nortel as an enhancement to standard multi-link trunking (MLT) as defined in IEEE 802.3ad. US 7173934,Lapuh, Roger; Zhao, Yili& Tawbi, Wassimet al.,"System, Device, and Method for Improving Communication Network Reliability Using Trunk Splitting",issued 2007-02-06 

Link aggregation or MLT allows multiple physical network links between two network switches and another device (which could be another switch or a network device such as a server) to be treated as a single logical link and load balance the traffic across all available links. For each packet that needs to be transmitted, one of the physical links is selected based on a load-balancing algorithm (usually involving a hash function operating on the source and destination MAC address information). For real-world network traffic this generally results in an effective bandwidth for the logical link equal to the sum of the bandwidth of the individual physical links. Redundant links that were once unused due to Spanning Tree’s loop protection can now be used to their full potential.

A general limitation of standard link aggregation, MLT or EtherChannel is that all the physical ports in the link aggregation group must reside on the same switch. The SMLT, DSMLT and RSMLT protocols remove this limitation by allowing the physical ports to be split between two switches, allowing for the creation of Active load sharing high availability network designs that meet five nines availability requirements.

SMLT topologies

SMLT triangle between 3 Avaya switches 40 Gbit/s full duplex to edge switch SMLT.JPG
SMLT triangle between 3 Avaya switches 40 Gbit/s full duplex to edge switch

The two switches between which the SMLT is split are known as aggregation switches and form a logical cluster which appears to the other end of the SMLT link as a single switch.

The split may be at one or at both ends of the MLT. If both ends of the link are split, the resulting topology is referred to as an "SMLT square" when there is no cross-connect between diagonally opposite aggregation switches, or an "SMLT mesh" when each aggregation switch has a SMLT connection with both aggregation switches in the other pair. If only one end is split, the topology is referred to as an SMLT triangle.

In an SMLT triangle, the end of the link which is not split does not need to support SMLT. This allows non-Avaya devices including third-party switches and servers to benefit from SMLT. The only requirement is that IEEE 802.3ad static mode must be supported.

Operation

Server SMLT triangle Server-SMLT.jpg
Server SMLT triangle

The key to the operation of SMLT is the Inter-Switch Trunk (IST). The IST is a (standard) MLT connection between the aggregation switches which allows the exchange of information regarding traffic forwarding and the status of individual SMLT links.

For each SMLT connection, the aggregation switches have a standard MLT or individual port with which an SMLT identifier is associated. For a given SMLT connection, the same SMLT ID must be configured on each of the peer aggregation switches.

For example, when one switch receives a response to an ARP request from an end station on a port that is part of an SMLT, it will inform its peer switch across the IST and request the peer to update its own ARP table with a record pointing to its own connection with the corresponding SMLT ID.

In general, normal network traffic does not traverse the IST unless this is the only path to reach a host which is connected only to the peer switch. By ensuring all devices have SMLT connections to the aggregation switches, traffic never needs to traverse the IST and the total forwarding capacity of the switches in the cluster is also aggregated.

The communication between peer switches across the IST allows both unicast and multicast routing information to be exchanged allowing protocols such as Open Shortest Path First (OSPF) and Protocol Independent Multicast-Sparse Mode (PIM-SM) to operate correctly.

Failure scenarios

SMLT

The use of SMLT not only allows traffic to be load-balanced across all the links in an aggregation group but also allows traffic to be redistributed very quickly in the event of link or switch failure. In general the failure of any one component results in a traffic disruption lasting less than half a second (normal less than 100 millisecond [3] [4] ) making SMLT appropriate in environments running time- and loss-sensitive applications such as voice and video.

In a network using SMLT, it is often no longer necessary to run a spanning tree protocol of any kind since there are no logical bridging loops introduced by the presence of the IST. This eliminates the need for spanning tree reconvergence or root-bridge failovers in failure scenarios which causes interruptions in network traffic longer than time-sensitive applications are able to cater for.

Product support

SMLT is supported within the following Avaya Ethernet Routing Switch (ERS) and Virtual Services Platform (VSP) Product Families: ERS 1600, ERS 5500, ERS 5600, ERS 7000, ERS 8300, ERS 8800, ERS 8600, MERS 8600, VSP 9000

SMLT is fully interoperable with devices supporting standard MLT (IEEE 802.3ad static mode).

R-SMLT

Routed-SMLT (R-SMLT) is a computer networking protocol developed at Nortel as an enhancement to split multi-link trunking (SMLT) enabling the exchange of Layer 3 information between peer nodes in a switch cluster for resiliency and simplicity for both L3 and L2. [5] [6]

In many cases, core network convergence time after a failure is dependent on the length of time a routing protocol requires to successfully converge (change or re-route traffic around the fault). Depending on the specific routing protocol, this convergence time can cause network interruptions ranging from seconds to minutes. The R-SMLT protocol works with SMLT and distributed Split Multi-Link Trunking (DSMLT) technologies to provide sub-second failover (normally less than 100 milliseconds) [7] so no outage is noticed by end users. This high speed recovery is required by many critical networks where outages can cause loss of life or very large monetary losses in critical networks.

RSMLT routing topologies providing an active-active router concept to core SMLT networks. The protocol supports networks designed with SMLT or DSMLT triangles, squares, and SMLT or DSMLT full mesh topologies, with routing enabled on the core VLANs. R-SMLT takes care of packet forwarding in core router failures and works with any of the following protocol types: IP Unicast Static Routes, RIP1, RIP2, OSPF, BGP and IPX RIP.

Product support

R-SMLT is supported on Avaya's Ethernet Routing Switch ERS 8600, ERS 8800, VSP9000, ERS 8300 and MERS 8600 products.

Avaya Distributed Multi-Link Trunking
DMLT between 2 stacked 5530 switches to an ERS 8600 switch DMLT.jpg
DMLT between 2 stacked 5530 switches to an ERS 8600 switch
DMLT between 2 stacked 5530 switches to an ERS 8600 switch

Distributed multi-link trunking (DMLT) or distributed MLT is a proprietary computer networking protocol designed by Nortel Networks, and now owned by Extreme Networks, [8] used to load balance the network traffic across connections and also across multiple switches or modules in a chassis. The protocol is an enhancement to the Multi-Link Trunking (MLT) protocol.

DMLT allows the ports in a trunk (MLT) to span multiple units of a stack of switches or to span multiple cards in a chassis, preventing network outages when one switch in a stack fails or a card in a chassis fails.

DMLT is described in an expired United States Patent. [9]

Distributed split multi-link trunking (DSMLT) or Distributed SMLT is a computer networking technology developed at Nortel to enhance the Split Multi-Link Trunking (SMLT) protocol. DSMLT allows the ports in a trunk to span multiple units of a stack of switches or to span multiple cards in a chassis, preventing network outages when one switch in a stack fails or one card in a chassis fails. US 6496502,Fite Jr., David B.; Ilyadis, Nicholas& Salett, Ronald M.,"Distributed Multi-Link Trunking Method and Apparatus",issued 2002-12-17 

Fault-tolerance is a very important aspect of Distributed Split Multi-Link Trunking (DSMLT) technology. Should any one switch, port, or more than one link fail, the DSMLT technology will automatically redistribute traffic across the remaining links. Automatic redistribution is accomplished in less than half a second (typically less than 100 milliseconds [10] ) so no outage is noticed by end users. This high speed recovery is required by many critical networks where outages can cause loss of life or very large monetary losses in critical networks. Combining Multi-Link Trunking (MLT), DMLT, SMLT, DSMLT and R-SMLT technologies create networks that support the most critical networks.

Product support

SMLT is supported on Avaya's Ethernet Routing Switch 1600, 5500, 8300, ERS 8600, MERS 8600, VSP-7000 and VSP-9000 products.

Related Research Articles

<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">Metro Ethernet</span> Metropolitan area network based on Ethernet standards

A metropolitan-area Ethernet, Ethernet MAN, carrier Ethernet or metro Ethernet network is a metropolitan area network (MAN) that is based on Ethernet standards. It is commonly used to connect subscribers to a larger service network or for internet access. Businesses can also use metropolitan-area Ethernet to connect their own offices to each other.

<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.

Virtual LACP (VLACP) is an Avaya extension of the Link Aggregation Control Protocol to provide a Layer 2 handshaking protocol which can detect end-to-end failure between two physical Ethernet interfaces. It allows the switch to detect unidirectional or bi-directional link failures irrespective of intermediary devices and enables link recovery in less than one second.

InterSwitch Trunk (IST) is one or more parallel point-to-point links that connect two switches together to create a single logical switch. The IST allows the two switches to share addressing information, forwarding tables, and state information, permitting rapid fault detection and forwarding path modification. The link may have different names depending on the vendor. For example, Brocade calls this an Inter-Chassis Link (ICL). Cisco calls this a VSL.

<span class="mw-page-title-main">Metro Ethernet Routing Switch 8600</span>

Metro Ethernet Routing Switch 8600 or MERS 8600 is a modular chassis router and/or switch manufactured by Nortel now acquired by Ciena. The MERS 8600 supports the Provider Backbone Bridges (PBB), Provider Backbone Transport (PBT) technologies and carrier class Operations Administration & Maintenance (OAM) tools.

<span class="mw-page-title-main">Avaya ERS 8600</span> Networking router and switch

The Avaya Ethernet Routing Switch 8600 or ERS 8600, previously known as the Passport 8600 or the Accelar 8000, is a modular chassis combination hardware router and switch used in computer networking. The system, originally designed and manufactured by Nortel, was manufactured by Avaya from 2009 until 2017. The system provided the 10G Ethernet equipment backbone for the 2010 Winter Olympics games, providing service for 15,000 VoIP Phones, 40,000 Ethernet connections and supporting 1.8 million live spectators. The system is configurable as a 1.440 Terabit Switch cluster using SMLT and R-SMLT protocols, to provide high reliability cluster failover.

<span class="mw-page-title-main">Avaya ERS 5500 Series</span> Series of networking switches

The Ethernet Routing Switch 5500 Series or is a series of stackable, Layer 3 switches used in computer networking. The ERS 5000 was originally designed by Nortel and is now manufactured by Avaya. Up to 8 ERS 5000 Series Switches may be stacked in a 640 Gbit/s fast stacking configuration. This Switch was used as the access layer device for the 2010 Winter Olympics games. The 817 Access Switches supported 8782 Voice-over-IP telephones.

Simple Loop Prevention Protocol (SLPP) in computer networking is a data link layer protocol developed by Nortel to protect against Layer 2 network loops. SLPP uses a small hello packet to detect network loops. The SLPP protocol checks packets from the originating switch and the peer switch in a SMLT configuration. Sending hello packets on a per VLAN basis allows SLPP to detect VLAN based network loops for un-tagged as well as tagged IEEE 802.1Q VLAN link configurations. If a loop is detected, the associated port is shut down.

<span class="mw-page-title-main">Avaya ERS 5600 Series</span> Series of routers

Ethernet Routing Switch 5600 Series or in computer networking terms are stackable routers and switches designed and manufactured by Avaya. The ERS 5600 Switches can be stacked up to 8 units high to create a 1.152 Tbit/s backplane through the Flexible Advanced Stacking Technology (FAST) stacking technology configuration. The 5600 Series consists of five stackable models that can be mixed and matched together with other ERS 5600 models or other ERS 5500 models to meet configuration requirements. Additionally the ports on the switches incorporates the Avaya Energy Saver (AES) which can manage and dim down the power requirements to save energy across all switches in the enterprise.

<span class="mw-page-title-main">Avaya VSP 9000 Series</span> Series of network switches

Avaya Virtual Services Platform 9000 Series or VSP 9000 is a set of modular chassis switches used in enterprise and data center networks, manufactured by Avaya. The VSP 9000 was targeted at institutions which were suffering from performance limitations, needed to simplify their network infrastructure in a virtualized environment, or required 10 Gigabit Ethernet with the option to scale to 40 or 100 Gigabit Ethernet. It is also an option for companies who are looking to reduce the power and cooling cost in order to maximize the cost-effectiveness of their infrastructures; this unit was also designed, and is expected, to have a lifespan of seven-to-ten years.

Avaya Ethernet Routing Switch 8800 Series or ERS 8800, is a range of modular chassis products that combine hardware router and switch used in computer networking, designed and manufactured by Avaya. When an ERS 8000 Chassis, a passive device in its own right, is equipped with the 8895 SF/CPU, this system is known as an Ethernet Routing Switch 8800; conversely, when equipped with an 8692 SF/CPU module the system is known as an Ethernet Routing Switch 8600.

<span class="mw-page-title-main">Avaya ERS 4000 series</span> Stackable switch/routers

Ethernet routing switch 4000 series or in computer networking terms are stackable layer-3 (routers) and layer-2 (switches) designed and manufactured by Avaya for Ethernet devices. The ERS 4000 series consists of two major groups of devices, the ERS 4500 models and the ERS 4800 models.

Fabric Connect, in computer networking usage, is the name used by Extreme Networks to market an extended implementation of the IEEE 802.1aq and IEEE 802.1ah-2008 standards.

<span class="mw-page-title-main">ERS 3500 and ERS 2500 series</span> Stackable routing switches

Ethernet Routing Switch 3500 series and Ethernet Routing Switch 2500 series or ERS 3500 and ERS 2500 in data computer networking terms are stackable routing switches designed and manufactured by Avaya.

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.

The Avaya Virtual Services Platform 4000 series are products that, in computer networking terms, are standalone switch/routers designed and manufactured by Avaya for Ethernet-based networks. The VSP 4000 hardware is a derivative of the earlier Ethernet routing switch 4000 series, leveraging certain shared components, but implementing a new, completely different, operating system derived from the virtual service platform 9000 series. The role of the VSP 4000 is to extend fabric-based network virtualization services to smaller, remote locations, thereby creating a single service delivery network.

A first hop redundancy protocol (FHRP) is a computer networking protocol which is designed to protect the default gateway used on a subnetwork by allowing two or more routers to provide backup for that address; in the event of failure of an active router, the backup router will take over the address, usually within a few seconds. In practice, such protocols can also be used to protect other services operating on a single IP address, not just routers.

References

  1. ↑ USpatent 6731599,Van Hunter, Joseph Regan, Alfred Nothaft, Akhil Duggal; Regan, Joseph& Nothaft, Alfredet al.,"Automatic Load Sharing-Trunking",issued 2004-05-04, assigned to Nortel Networks Limitedand Avaya Holdings Limited
  2. ↑ "Evaluation of Resilient Routing Switches for Real-Time Multimedia Traffic with Microsoft Live Communications Server 2005 and Nortel MCS 5100" (PDF). The Tolly Group. Archived from the original (PDF) on 2011-07-25. Retrieved 2007-06-25.
  3. ↑ "Evaluation of Resilient Routing Switches for Real-Time Multimedia Traffic with Microsoft Live Communications Server 2005 and Nortel MCS 5100" (PDF). The Tolly Group. Archived from the original (PDF) on 2011-07-25. Retrieved 2007-06-25.
  4. ↑ "National University of Malaysia Unleashes Student Learning With Nortel; New High Performance Network To Enhance New Educational Approaches". M2 Presswire. June 17, 2009. Retrieved 2 Sep 2011. The network will utilize Nortel's SMLT (Split Multi-Link Trunking) technology, which provides exceptional resiliency to ensure voice, video and other applications stay connected despite link, switch or site equipment failures.[ dead link ]
  5. ↑ US 7463579,Lapuh, Roger&Tamiji, Homma,"Routed Split Multilink Trunking",issued 2008-12-09
  6. ↑ US 8861338,Lissianoi, Sergei,"Routed Split Multilink Trunking for IPv6",issued 2014-10-14
  7. ↑ "Evaluation of Resilient Routing Switches for Real-Time Multimedia Traffic with Microsoft Live Communications Server 2005 and Nortel MCS 5100" (PDF). The Tolly Group. Archived from the original (PDF) on 2011-07-25. Retrieved 2007-06-25.
  8. ↑ Nortel Networks (2008). "Patent US6496502" . Retrieved July 10, 2012.
  9. ↑ David B. Fite Jr.; Nicholas Ilyadis; Ronald M. Salett (December 17, 2002). "Distributed multi-link trunking method and apparatus". United States Patent and Trademark Office . Retrieved 3 Sep 2011.
  10. ↑ "Evaluation of Resilient Routing Switches for Real-Time Multimedia Traffic with Microsoft Live Communications Server 2005 and Nortel MCS 5100" (PDF). The Tolly Group. Archived from the original (PDF) on 2011-07-25. Retrieved 2007-06-25.
  1. US 7173934 Lapuh, Roger & Yili Zhao "System, device, and method for improving communication network reliability using trunk splitting"; (SMLT) issued 2007-02-06

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