LACP behaviour

Hi ,

I have a query regarding link aggregation.What is the expected behaviour for a switch which peer is not sending any BDPU ,both are configured on LACP .

Should LACP enabled ports be put into operational down if they dont get BPDU's from partners ?

Where do I get these standard ?

BR, Gaurav

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The Bridge Relay function (i.e., the entity that performs LAN switching and which sends/receives BPDUs runs *above* the Link Aggregation function. That is, from the perspective of the bridge relay, all of the physical interfaces comprising the aggregation appear as a single LAN port.

The switch will decide which ports are enabled/disabled for transmission (ports are always allowed to receive, in order to detect BPDUs) per the Spanning Tree Protocol (or its descendants: RSTP, MSTP) based on the reception (or not) of BPDUs. In general, a port will be enabled for transmission unless the bridge receives a BPDU on that port indicating that another device has a greater claim to be the Designated Bridge for that LAN.

There is a good discussion of the Spanning Tree Protocol in Chapter 5 of "The Switch Book." LACP and Link Aggregation is discussed in Chapter 9.

All IEEE 802 standards are available free of charge at:

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STP is part of IEEE 802.1D. Link Aggregation is (currently) part of IEEE 802.3 (but will be moving to IEEE 802.1 soon).

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