Link Aggregation Control Protocol


Link Aggregation Control Protocol

The Link Aggregation Control Protocol (LACP) is a computer networking term and is part of IEEE specification 802.3ad that can control the bundling of several physical ports together to form a single logical channel. LACP allows a network device to negotiate an automatic bundling of links by sending LACP packets to the peer (directly connected device that also implements LACP).

Advantages

* Failover when a link fails and there is a Media Converter (For Example) between the devices which means that the peer will not see the link down. With a static link aggregation the peer would continue sending traffic down the link causing it to be lost.
* The device can confirm that the other end is configured for link aggregation. With Static link aggregation a cabling or configuration mistake could go undetected and cause undesirable network behavior. [ [http://support.dell.com/support/edocs/network/LAG1855/LAGConsiderationv0.5.pdf Link aggration on Dell servers] ]
* For the advantages of combining links into a single logical link please see Link aggregation.

Practical notes

LACP works by sending frames (LACPDUs) down all links that have the protocol enabled. If a device is present on the other end of the link that also has LACP enabled, it will also independently send frames along the same links enabling the two units to detect multiple links between themselves and then combine them into a single logical link. LACP can be configured in one of two modes: Active or Passive. In Active mode it will always send frames along the configured links. In passive mode however, it acts as "speak when spoken to", and therefore can be used as a way of controlling accidental loops (as long as the other device is in active mode). [ [http://www.ieee802.org/3/ad/ IEEE 802.3ad Link Aggregration Task Force] ]

See also

* Link aggregation
* Virtual LACP (VLACP): A Nortel enhancement to the Link Aggregation Control Protocol
* Multi-Link Trunking (MLT): Nortel's Port Aggregation Protocol
* Split multi-link trunking (SMLT): Nortel's proprietary enhancement to MLT
* Routed-SMLT (RSMLT): Nortel's proprietary Layer-3 enhancement to SMLT
* Port Aggregation Protocol (PAgP): Cisco's proprietary protocol provides similar function as and pre-dates LACP
* EtherChannel

References

External links

* [http://www.ieee802.org/3/ad/ IEEE 802.3ad Link Aggregration Task Force]
* [http://www.cisco.com/en/US/products/ps6566/products_feature_guide09186a008071860b.html Cisco - Link Aggregation Control Protocol (LACP) (802.3ad) for Gigabit Interfaces]
* [http://www.juniper.net/techpubs/software/junos/junos90/swconfig-network-interfaces/exampleconfiguring-aggregated-ethernet-lacp.html Juniper M/T/J Series - Link Aggregation Control Protocol (LACP) (802.3ad) for Aggregated Ethernet Interfaces]
* [http://www.juniper.net/techpubs/software/erx/junose90/swconfig-physical/html/ethernet-config14.html Juniper E-Series - Link Aggregation Control Protocol (LACP) (802.3ad) for Aggregated Ethernet Interfaces]


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