LACP not prioritizing desired ports
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I’ve got two 10 GbE fiber links and one 1 GbE Cat6 link between switch A (TL-SG3428XMP 3.0, 3.0.2 Build 20221130 Rel.57838) and switch B (TL-SG3210XHP-M2 2.0, firmware firmware 2.0.0 Build 20220322 Rel.62255). I want to use both the fiber links and fall back to the Cat6, so I’ve configured exactly one LACP group (ID 2, chosen at random) on each switch, containing the fiber ports at the default priority of 32768 and the Cat6 port at 65000. Switch A is the active side.
Whenever switch B is rebooted, the 1 GbE link is what comes up. The only entry on the LAG Table page is the Cat6 port, and the LACP Config page only shows LAG2 on that port (on both sides). If I unplug the Cat6 cable, both fiber ports become active (reflected on the LAG Table and LACP Config pages), and plugging the Cat6 cable back in later doesn’t change anything.
My understanding is that a lower number denotes a higher priority. Is there something I need to change in order to make it work correctly? I don’t see why it should be using the Cat6 link except as a fallback.
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Hi @shivjm
Then here is my question, how do you verify that LACP does not prioritize these SFP ports?
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@Clive_A I can see that the LAG Table shows only the 1 GbE link whenever I restart switch B (see my screenshots from earlier) and I’ve verified with iperf3 that it is in fact using that link. I can also see the LAG Table update when I unplug the copper link, like in this screenshot from the passive side:
And I can see the difference in speed in iperf3 in that situation. Note that if I make the fiber links work like this and then plug the copper link back in, it doesn’t revert to using the copper link; it stays on the fiber links.
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Hi @shivjm
Thanks for posting in our business forum.
shivjm wrote
@Clive_A I can see that the LAG Table shows only the 1 GbE link whenever I restart switch B (see my screenshots from earlier) and I’ve verified with iperf3 that it is in fact using that link. I can also see the LAG Table update when I unplug the copper link, like in this screenshot from the passive side:
And I can see the difference in speed in iperf3 in that situation. Note that if I make the fiber links work like this and then plug the copper link back in, it doesn’t revert to using the copper link; it stays on the fiber links.
So I confirmed this with the senior engineers, don't LAG two different ports of link speed at the same time. It does not work. You can set it but it won't take effect. There is a potential that the MAC address table would go in error.
So, if you set a LAG group, set the same link speed ports in the same LAG group. Don't mix them up.
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Thanks, @Clive_A. That’s disappointing—the Cisco documentation @KJK linked implies other vendors do support it, so I’m sad to see it’s not possible here. Fortunately, it’s not a major hindrance in this particular case since the 1 GbE link is only a failsafe. I suppose I can keep that port disabled as long as the two 10 GbE links are up.
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The switches that do not allow me to activate LACP on LAGs with links of different speeds are actually CISCO small business switches. When I try to do that, and I have never tried that before your post, I get an error message complaining about it and the switch accepts only the 1G port as a LAG candidate. The 10G ports are droped from the candidate list.
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Hi @shivjm
Thanks for posting in our business forum.
shivjm wrote
Thanks, @Clive_A. That’s disappointing—the Cisco documentation @KJK linked implies other vendors do support it, so I’m sad to see it’s not possible here. Fortunately, it’s not a major hindrance in this particular case since the 1 GbE link is only a failsafe. I suppose I can keep that port disabled as long as the two 10 GbE links are up.
So, see the KJK's reply. That kills the conversation and only increases your disappointment.
That looks like what an industry does. Not your, my, and our(company's) call. You probably check the standard and see if it is even possible from the theory instead of whining about it. Cisco as the leader in this industry does not do that, which might be impossible from the theory.
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@KJK, thanks, I appreciate the extra information (and your attempts to help me in general). I was going by the docs you shared, which I’ll quote here for reference in case anyone else is misled by them and comes to the same conclusion I did:
Any link operating at a different speed from the highest-speed active member or operating at half-duplex is made standby. All the active ports in a dynamic LAG operate at the same baud rate.
@Clive_A, if you consider it whining to use a word as mild and polite as ‘disappointing’, I think support may not be for you. I’m shocked to see this petulant and immature behaviour in a forum for business products, especially after the ordinary and fruitful conversation we’ve had in this thread. I’m under no obligation to genuflect at the altar of TP-Link’s engineering, and I don’t expect someone whom I’ve spoken to with courtesy and patience throughout to upbraid me for saying the conclusion is not the desired outcome. I definitely won’t be buying or recommending any more TP-Link products after your response.
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