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I did research and found that below are the minimum requirements for LACP to be Up.

  1. One of the side should be active.
  2. All the port speed should be same.
  3. Duplex settings need to be same.

Also I have found few other things.

A. The media would need to be same. As in 1G Ethernet and 1G Fiber are not allowed. 
B. VLAN passed on both the sides should match.

I am not understanding why both the points A and B are required to make LACP come Up. Can anyone explain the logic here or correct me if I am wrong.

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A. The media would need to be same. As in 1G Ethernet and 1G Fiber are not allowed.

This isn't actually required in many implementations, but some vendors do restrict this. It may have technical reasons (different PCS sublayer variants for -T, -X, or -R, so different encoding engines/chips may be used) or just that the implementer is overly compliant. Many implementations don't mind different media.

802.1AX doesn't care about the medium, there is no such requirement mentioned. (AX doesn't even prohibit different link speeds but explicitly leaves out traffic distribution over such a LAG, see IEEE 802.1AX Clause 6.1.1).

B. VLAN passed on both the sides should match.

Of course, VLAN associations across a LAG trunk need to be uniform. Since most (all?) implementations regard a LAG trunk as a single logical interface and ignore/delete the previous physical interface configuration, that is a non-issue.

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  • Thank you very much for the response. First point makes absolutely sense. However I am still not convinced on the second point. Reason being, if on either ends are part of different vlan, how would that impact the LACP. As an example. Switch A lag1 is tagged to vlan 2 Switch B lag1 is tagged to vlan 2,3. Both lag1 have port 1/1/1 part of it. This would still form the lag right ? VLAN 3 communication might be impacted but vlan 2 atleast should work. And if VLAN 2 is working. It would mean that the lag is working, right? @Zac67 – Neil Roy Sep 5 at 13:32
  • Of course, you could configure each side's VLANs differently. Of course, those mismatched VLANs wouldn't work, not different from a single link. LAG/LACP is below the actual L2/MAC layer, so the link forms regardless of the "upper" VLAN config. – Zac67 Sep 5 at 13:40
  • Perfect. That logically makes sense. Thank you very much for your response :) @Zac67 – Neil Roy Sep 5 at 13:42
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Most of the issues with Etherchannels (Link Aggregation) are because of misconfiguration. Keep in mind that the configuration of all physical interfaces has to match. Here's a look at some common parameters that need to match at both end to ensure LACP link to come up.

We can see that device1 has been configured for LACP and device 2 for PAgP, it will don't work because both sides should be LACP or both side should be pAgP

LACP is configured for passive or active mode. Interfaces in active mode will “actively” try to form an etherchannel. Interfaces in passive mode will only respond to LACP requests. So you can configure active and passive on each side to make link to come up

Must be configured both as trunk ports should be same mode of Port

Must be same matching bandwidth on either side to make LACP come up

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  • I completely agree with your answer except the last point."Must be configured with the same VLANs at both ends". I dont think the last point is valid for the LACP at-least to come Up. @Ron Trunk – Neil Roy Sep 5 at 13:44
  • @NeilRoy Since you dragged me into this...It’s not a requirement of LACP itself, but most vendors’ implementation checks for Vlan mismatch since that would cause thing to break in mysterious ways. – Ron Trunk Sep 5 at 14:40
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  • The point A is based in how the bits are send across the media, the copper cable send electrical signals and the fiber optic transport light. This is a mismatch let says of technologies in layer 1.
  • The point B is refers that port channel cannot merge the Vlans allowed of the physical interfaces once you add to your ports to the port channel, only the interfaces that have the same Vlans allowed on both sides will be part of the bundle(port channel) the other that mismatch this will be placed in Down state.
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