Hello,
First of all, I agree that the comment in the first article the different port numbering was quite confusing (even to me), so I have removed this from the article, as - as already mentioned earlier - it’s not necessary to use different ports.
Rather the opposite even. Using the same ports makes configuration much more simpler, i.e. when using “orchestration” (the simultaneous configuration of both MLAG peers). Also troubleshooting would be quite painful when the ports on the MLAG peers are different.
I also corrected some other small points, but left majority of the article as it was.
In regards to the second article, when it comes to STP on the MLAG ports, the MLAG peers determine between each other which one is considered the “STP master” and only this switch will send the STP BPDU’s out the MLAG ports, as otherwise the connected device would receive the BDPU’s twice - once from each MLAG peer, and this is obviously not wanted.
The way they determine who’s said “STP master” is based on the MLAG indices and can be different per MLAG port. One MLAG peer will handle all the odd indices and the other the even ones.
Let’s say for example, you’re having 6 switches you want to connect via MLAG and are therefore using 6 MLAG ports with MLAG indices 101,102,103,104, 105 and 106, then one MLAG peer will send out the STP BPDU’s on the MLAG ports that are configured for indices 101,103 and 105, and the other MLAG peer will send them out on the ports configured for indices 102, 104 and 106.
Let’s say you have one of the MLAG peers acting as a root bridge for an STP domain and you want the switches connected to all 6 MLAG ports to participate in STP, then you may want this root-bridge-MLAG peer to send out the BPDU’s to all of the MLAG ports. To achieve this you would have to use either only odd or even MLAG indices (so i.e. 101,103,105,107, 109 and 111 OR 100,102,104,106, 108 and 110 if we stick with the “6 MLAG ports” example), as this would mean that the same MLAG peer is the “STP master”.
The mentioned “unpredictable convergence behavior” (and that’s why it’s mentioned that it’s a “best practice”) is that if the MLAG-STP mastership is shared between the two MLAG peer switches, in case of a reboot of one of them, half of the connected switches/devices would receive an STP TC, while the other half doesn’t.
I hope this helped clear this up a bit.
Chris
