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A multi-chassis link aggregation group (MLAG or MC-LAG) 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 for coordination between chassis is proprietary.
A LAG is a method of inverse multiplexing 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 MAC client can treat the Link Aggregation Group as if it were a single link." [1] This layer 2 transparency is achieved by the LAG using a single MAC address 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 Link Aggregation Control Protocol (LACP), for control. This LACP protocol is also defined within the 802.1AX-2008 standard.
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. [2] Nodes in an MC-LAG cluster communicate to synchronize and negotiate automatic switchovers (failover). Some implementations may support administrator-initiated (manual) switchovers.
The diagram here shows four configurations:
The HA configuration is superior to spanning tree. Load can be shared across all links during normal operation, whereas spanning tree must disable some links to prevent loops.
The following table lists known vendor implementations of MC-LAG, all of which are proprietary.
Vendor | Implementation Name |
---|---|
ADVA Optical Networking | MC-LAG |
Arista Networks | MLAG |
Aruba Networks (formerly HP ProCurve) | Distributed Trunking under Intelligent Resilient Framework switch clustering technology |
Avaya | Distributed Split Multi-Link Trunking |
Ruckus Networks (formerly Brocade) | Multi-Chassis Trunking |
Ciena | MC-LAG |
Cisco Catalyst 6500 | Multichassis Etherchannel (MEC) - Virtual Switching System (VSS) |
Cisco Catalyst 3750 (and similar) | Cross-Stack EtherChannel |
Cisco Catalyst 9000 | StackWise Virtual |
Cisco Nexus | Virtual PortChannel (vPC), where a PortChannel is a regular LAG |
Cisco IOS XR | mLACP (Multichassis Link Aggregation Control Protocol) |
Cumulus Networks | MLAG (formerly CLAG) |
Dell Networking (formerly Force10 Networks, formerly nCore) | DNOS6.x Virtual Port Channel (vPC) or Virtual Link Trunking |
Edgecore Networks | MLAG |
Extreme Networks | MLAG (Multi Switch Link Aggregation Group) |
Ericsson | MC-LAG (Multi Chassis Link Aggregation Group) |
FS | MLAG |
Fortinet | MC-LAG (Multi Chassis Link Aggregation Group) |
H3C | Distributed Resilient Network Interconnect |
Huawei | M-LAG |
Juniper | MC-LAG |
Lenovo Networking (formerly IBM) | vLAG |
Mellanox Technologies | MLAG |
MikroTik | MLAG [3] |
NEC | MC-LAG (Openflow to traditional network) |
Nocsys | MLAG |
Netgear | MLAG |
Nokia (Formerly Alcatel-Lucent) | MC-LAG |
Nortel | Split multi-link trunking |
Nuage Networks (from Nokia) | MC-LAG ; including MCS (Multi-chassis Sync) |
Plexxi (now Aruba Networks)) | vLAG |
Pluribus Networks (now Arista Networks) | vLAG |
UniFi | MC-LAG [4] |
ZTE | MC-LAG |
IEEE 802.1aq (Shortest Path Bridging) is an alternative to MC-LAG that can be used for complex networks. [5]
TRILL (TRansparent Interconnection of Lots of Links) facilitates an Ethernet to have an arbitrary topology, and enables per flow pair-wise load splitting by way of Dijkstra's algorithm, without configuration and user intervention.
Ethernet is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.
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