Link Aggregation Control Protocol - IEEE 802

1 Rev. Saturday, March 7 19991 link Aggregation Control ProtocolMick SeamanWhile not reiterating basic concepts, this note attempts a complete description of theprotocol, with the exception of flush mechanisms which are orthogonal to LACP revision summarizes my understanding1 of the link Aggregation ControlProtocol described in and proposes some minor changes. The latter flesh out thepreviously agreed manual configuration defaults for Partner parameters. These were notfully incorporated into , as is highlighted by the Editor s Note on page 96 of the proposed changes result in some simplification of the state machines, particularly ofthe periodic machine, as well as increased flexibility in Protocol use.

2 The informationcommunicated by the Protocol is description given in Rev and Rev of this note has also been updated to reflectthe management terminology and the shared variable communication statemachine conventions used in separate note describes possible Protocol extensions, outside the scope of theproposed standard, that ensure predictable Protocol operation for links attached to sharedmedia. Such links cannot occur if standard equipment is used: the scope of theproposed link Aggregation standard is limited to full duplex links, and there is nostandardized full duplex note is not a ballot comment, but provides background for ballot comments in theusual form.

3 Most of the commentary on proposed changes is provided as footnotes, toallow me to strip these out as and when ballot comments are resolved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

4 Q WKLV UHYLVHG GHVFULSWLRQ WKH UHFHLYH PDFKLQH DQG PDWFK ORJLF WRJHWKHUQRZ VLJQDO QRW VHOHFWHG WR WKH VHOHFWLRQ ORJLF DQG PDWFKHG QRW PDWFKHG WR WKH PX[ FRQWURO PDFKLQH 7KH SHULRGLF WUDQVPLVVLRQ PDFKLQHRSHUDWHV GLUHFWO\ RQ WKH UHOHYDQW RSHUDWLRQDO VWDWH YDULDEOHV DQG GRHV QRW UHTXLUH DQ\ DGGLWLRQDO VLJQDOOLQJ YDULDEOHV 7KH VLJQDOLQJ RI QHHG WRWUDQVPLW WKURXJK VHWWLQJ RI WKH YDULDEOH QWW E\ YDULRXV PDFKLQHV LV XQFKDQJHG WKHUH LV RQO\ RQH UHFLSLHQW RI WKH VLJQDO WKH WUDQVPLVVLRQPDFKLQH Rev. Saturday, March 7 19992 Protocol ParticipantsThe Protocol is described from the point of viewof the physical ports, that represent a singlepoint of attachment to a transmission physical port that may be aggregated withother physical ports is a participant in is modelled by the attachment ofone or more physical ports to a Mux thatdistributes and collects frames from and to theaggregate port3.]

5 Aggregate ports represent apoint of attachment of higher layer the familiar case of individual links there is atrivial one to one correspondence betweenphysical and aggregate ports which is so obviousthat we do not distinguish it is clear that Protocol exchangesbetween participants in separate systems arebeing discussed (rather than the aggregatebehavior of participants in a single system) theterm participants refers to the local participant,sometimes called the actor for clarity, and hisremote partner . Protocol Data UnitsA single message type, the LACPDU, istransmitted by Protocol participants. It comprisesthe following information both for the transmittingactor, and its remote partner : the partnerinformation being the actor s current view of itspartners parameters.

6 Port Number System ID Key StatusThe Status information communicatedcomprises the following flags6: LACP_Activity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

7 W LV SURSRVHG WKDW WKHVH IODJV EH HQFRGHG LQ D /$& 3'8 DV ELWVLQ D WUDQVPLWWHG RFWHW 6 LQFH RQO\ IODJV DUH FXUUHQWO\ GHILQHG WKHWUHDWPHQW RI WKH WZR VSDUH IODJV LV H[SOLFWO\ GHILQHG WR IDFLOLWDWHLQWHURSHUDELOLW\ DQG SURWRFRO XSJUDGHDELOLW\ VKRXOG WKDW HYHU EHGHVLUHG $OO WKH UHFHLYHG IODJV DUH UHIOHFWHG LQWR WKH DFWRU V YLHZ RIWKH SDUWQHU V VWDWH LACP_Timeout Aggregate Synchronization Collecting DistributingThe LACP_Activity flag indicates a participant sintent to transmit periodically to detect andmaintain aggregates. If set7 the flagcommunicates Active LACP, if reset PassiveLACP. A passive participant will participate in theprotocol if it has an active LACP_Timeout flag indicates that theparticipant wishes to receive frequent periodictransmissions8, and will aggressively times outreceived information.]

8 If set the flagcommunicates Short Timeout, if reset Aggregation flag indicates that theparticipant will allow the link to be used as part ofan aggregate. Otherwise the link is to be used asan individual link , not aggregated with anyother. This flag is set or reset as a consequenceof local key management : the participant mayknow that the link has a unique key9 and hencewill not be aggregated. Signaling this informationallows the receiving actor to skip Protocol delaysthat are otherwise invoked to allow all links withthe same system id and key combinations to becollected into one aggregate port withoutsuccessive rapid changes to aggregate portsand accompanying higher layer If set the flag communicatesAggregatable, if reset Synchronization flag indicates that thetransmitting participant s mux component is insync with the system id and key informationtransmitted.

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10 Saturday, March 7, 19993hardware11 that takes time to set up If set the flag communicate InSync, if reset Out of Collecting flag indicates that theparticipant s collector, the receptioncomponent of the mux, is definitely on. If set theflag communicates Distributing flag indicates that theparticipant s distributor is not definitely off. Ifreset the flag indicates not MachineAs an aid to understanding and analysis theprotocol machine for each participant ispartitioned into the following components: Receive Machine Match Logic Periodic Transmission Machine Selection Logic Mux Control Logic and Machine Churn Detection Machine Transmit MachineThe Receive Machine maintains partnerinformation, recording Protocol information fromLACPDUs sent by remote partner(s).