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Multi-chassis link aggregation group
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<h2 id="background">Background</h2> <p>A LAG is a method of <a href="/facts/Inverse_multiplexing/e1VbGa17">inverse multiplexing</a> over multiple Ethernet links, thereby increasing bandwidth and providing redundancy. It is defined by the IEEE 802.1AX-2008 standard, which states, "Link Aggregation allows one or more links to be aggregated together to form a Link Aggregation Group, such that a <a href="/facts/Medium_access_control/hFpNzFFD">MAC</a> client can treat the Link Aggregation Group as if it were a single link."<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> This layer 2 transparency is achieved by the LAG using a single <a href="/facts/MAC_address/SVcTfgUH">MAC address</a> for all the device’s ports in the LAG group. LAG can be configured as either static or dynamic. Dynamic LAG uses a peer-to-peer protocol, called <a href="/facts/Link_Aggregation_Control_Protocol/3BE3qHDT">Link Aggregation Control Protocol</a> (LACP), for control. This LACP protocol is also defined within the 802.1AX-2008 standard. </p> <h2 id="multi-chassis">Multi-chassis</h2> <p>MC-LAG adds node-level redundancy to the normal link-level redundancy that a LAG provides. This allows two or more nodes to share a common LAG endpoint. The multiple nodes present a single logical LAG to the remote end. Note that MC-LAG implementations are vendor-specific, but cooperating chassis remain externally compliant to the IEEE 802.1AX-2008 standard.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> Nodes in an MC-LAG cluster communicate to synchronize and negotiate automatic switchovers in the event of failure. Some implementations may support administrator-initiated switchovers. </p><p>The diagram here shows four configurations: </p> <ol><li>Switches A and B are each configured to group four discrete links (as indicated in green) into a single logical link with four times the bandwidth. Standard LACP protocol ensures that if any of the links go down, traffic will be distributed among the remaining three.</li> <li>Switch A is replaced by two chassis, switches A1 and A2. They communicate between themselves using a proprietary protocol and are thereby able to masquerade as a single virtual switch A running a shared instance of LACP. Switch B is not aware that it is connected to more than one chassis.</li> <li>Switch B is also replaced by two chassis B1 and B2. If these switches are from a different vendor, they may use a different proprietary protocol between themselves. But virtual switches A and B still communicate using LACP.</li> <li>Crossing two links to form an X makes no difference logically, any more than crossing links in a normal LAG would. However, physically, it provides much improved fault tolerance. If any of the switches fail, LACP reconfigures paths in as little as a few seconds. Operation continues with paths existing between all sources and destinations, albeit with degraded bandwidth.</li></ol> <h2 id="implementations">Implementations</h2> <p>The following table lists known vendor implementations of MC-LAG, all of which are proprietary. </p> <table><tbody><tr><th>Vendor</th><th>Implementation Name</th></tr><tr><td><a href="/facts/ADVA_Optical_Networking/9kTsQ4eX">ADVA Optical Networking</a></td><td>MC-LAG</td></tr><tr><td><a href="/facts/Arista_Networks/125qgMKV">Arista Networks</a></td><td>MLAG</td></tr><tr><td><a href="/facts/Aruba_Networks/WlTuX66v">Aruba Networks</a> (formerly HP ProCurve)</td><td>Distributed Trunking under <a href="/facts/Intelligent_Resilient_Framework/uFC6BJjL">Intelligent Resilient Framework</a> switch clustering technology</td></tr><tr><td><a href="/facts/Avaya/FcS0TJcg">Avaya</a></td><td>Distributed Split Multi-Link Trunking</td></tr><tr><td><a href="/facts/Ruckus_Networks/XAlvVWzD">Ruckus Networks</a> (formerly Brocade)</td><td>Multi-Chassis Trunking</td></tr><tr><td><a href="/facts/Ciena/sXmaPYLS">Ciena</a></td><td>MC-LAG</td></tr><tr><td><a href="/facts/Cisco/ocDgQt6T">Cisco</a> Catalyst 6500</td><td>Multichassis Etherchannel (MEC) - Virtual Switching System (VSS)</td></tr><tr><td><a href="/facts/Cisco/ocDgQt6T">Cisco</a> Catalyst 3750 (and similar)</td><td>Cross-Stack EtherChannel</td></tr><tr><td><a href="/facts/Cisco/ocDgQt6T">Cisco</a> Catalyst 9000</td><td>StackWise Virtual</td></tr><tr><td><a href="/facts/Cisco/ocDgQt6T">Cisco</a> Nexus</td><td><a href="/facts/Virtual_PortChannel/FSXsLMof">Virtual PortChannel</a> (vPC), where a PortChannel is a regular LAG</td></tr><tr><td><a href="/facts/Cisco/ocDgQt6T">Cisco</a> IOS XR</td><td>mLACP (Multichassis Link Aggregation Control Protocol)</td></tr><tr><td><a href="/facts/Cumulus_Networks/f77bzVXV">Cumulus Networks</a></td><td>MLAG (formerly CLAG)</td></tr><tr><td><a href="/facts/Dell_Networking/4FSpcaq2">Dell Networking</a> (formerly Force10 Networks, formerly nCore)</td><td>DNOS6.x Virtual Port Channel (vPC) or <a href="/facts/Virtual_Link_Trunking/aqHRfery">Virtual Link Trunking</a></td></tr><tr><td>Edgecore Networks</td><td>MLAG<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></td></tr><tr><td><a href="/facts/Extreme_Networks/KvjBGmj2">Extreme Networks</a></td><td>MLAG (Multi Switch Link Aggregation Group)</td></tr><tr><td><a href="/facts/Ericsson/yJ4oMMp7">Ericsson</a></td><td>MC-LAG (Multi Chassis Link Aggregation Group)</td></tr><tr><td><a href="https://www.fs.com">FS</a></td><td>MLAG</td></tr><tr><td><a href="/facts/Fortinet/VWqDcpKN">Fortinet</a></td><td>MC-LAG (Multi Chassis Link Aggregation Group)</td></tr><tr><td><a href="https://www.h3c.com/en">H3C</a></td><td>Distributed Resilient Network Interconnect</td></tr><tr><td><a href="/facts/Huawei/Qwu0tbnL">Huawei</a></td><td>M-LAG</td></tr><tr><td><a href="/facts/Juniper_Networks/Vw0DBzXP">Juniper</a></td><td>MC-LAG</td></tr><tr><td><a href="/facts/Lenovo/4UNdKGUU">Lenovo</a> Networking (formerly IBM)</td><td>vLAG</td></tr><tr><td><a href="/facts/Mellanox_Technologies/FcpB6kPy">Mellanox Technologies</a></td><td>MLAG</td></tr><tr><td><a href="/facts/MikroTik/7TlAoXby">MikroTik</a></td><td>MLAG<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></td></tr><tr><td><a href="/facts/NEC/YnlUsMBA">NEC</a></td><td>MC-LAG (Openflow to traditional network)</td></tr><tr><td>Nocsys</td><td>MLAG</td></tr><tr><td><a href="/facts/Netgear/jCMtPgpD">Netgear</a></td><td>MLAG</td></tr><tr><td><a href="/facts/Nokia/bCleFoF4">Nokia</a> (Formerly Alcatel-Lucent)</td><td>MC-LAG</td></tr><tr><td><a href="/facts/Nortel/VYJnskS6">Nortel</a></td><td><a href="/facts/Split_multi-link_trunking/n5D9HW90">Split multi-link trunking</a></td></tr><tr><td><a href="https://www.nuagenetworks.net">Nuage Networks</a> (from <a href="/facts/Nokia/bCleFoF4">Nokia</a>)</td><td>MC-LAG ; including MCS (Multi-chassis Sync)</td></tr><tr><td>Plexxi (now <a href="/facts/Aruba_Networks/WlTuX66v">Aruba Networks</a>))</td><td>vLAG</td></tr><tr><td><a href="https://pluribusnetworks.com">Pluribus Networks</a> (now <a href="/facts/Arista_Networks/125qgMKV">Arista Networks</a>)</td><td>vLAG</td></tr><tr><td><a href="/facts/Ubiquiti/JrHJR8ed">UniFi</a></td><td>MC-LAG<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></td></tr><tr><td><a href="/facts/ZTE/h3CSA2gX">ZTE</a></td><td>MC-LAG</td></tr></tbody></table> <h2 id="alternatives">Alternatives</h2> <p>The link aggregation configuration is superior to <a href="/facts/Spanning_Tree_Protocol/ofHHMBuM">Spanning Tree Protocol</a> as the load can be shared across all links during normal operation, whereas Spanning Tree Protocol must disable some links to prevent loops. With Spanning Tree Protocol there is a potential delay when recovering from failure. Link aggregation typically can recover quickly from failure. </p><p><a href="/facts/IEEE_802.1aq/xslEBCKB">IEEE 802.1aq</a> (Shortest Path Bridging) is an alternative to MC-LAG that can be used for complex networks.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p><p><a href="/facts/TRILL/7lHM52Xe">TRILL</a> (TRansparent Interconnection of Lots of Links) allows <a href="/facts/Ethernet/nMfhU8tU">Ethernet</a> to use an arbitrary <a href="/facts/Network_topology/rBYE0kke">topology</a>, and enables per-flow pair-wise load splitting by way of <a href="/facts/Dijkstra%2527s_algorithm/ehun88jl">Dijkstra's algorithm</a> without configuration or user intervention. </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>IEEE. IEEE 802.1AX-2008. IEEE. <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Bhagat, Amit N. "Multichassis Link Aggregation Group". Google Knowledge Base. Retrieved 15 March 2012. <a href="https://sites.google.com/site/amitsciscozone/link-aggregation/multichassis-link-aggregation-group" target="_blank">https://sites.google.com/site/amitsciscozone/link-aggregation/multichassis-link-aggregation-group</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Aviz offers Networking 3.0". Retrieved 2025-04-06. <a href="https://www.edge-core.com/sonic/aviz-networks/aviz-offers-networking3/" target="_blank">https://www.edge-core.com/sonic/aviz-networks/aviz-offers-networking3/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>MikroTik: Multi-chassis Link Aggregation Group <a href="https://help.mikrotik.com/docs/display/ROS/Multi-chassis+Link+Aggregation+Group" target="_blank">https://help.mikrotik.com/docs/display/ROS/Multi-chassis+Link+Aggregation+Group</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>(Enterprise Aggregate Switches) <a href="https://store.ui.com/us/en/category/all-switching/products/ecs-aggregation" target="_blank">https://store.ui.com/us/en/category/all-switching/products/ecs-aggregation</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Mike Fratto (2011-03-07). "When MLAG Is Good Enough". Network Computing. <a href="https://www.networkcomputing.com/networking/when-mlag-good-enough" target="_blank">https://www.networkcomputing.com/networking/when-mlag-good-enough</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> </ol>