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I currently have two links which form a Port-Channel from 1 cisco device to another.

I want to change the port-channel config from

channel-group 1 mode on

to

channel-group 1 mode active

So that the Port-Channel is now running LACP, so I can also turn on lacp rate fast

To prevent any outage I was going to shut 1 of the interfaces in the Port-Channel change to LACP and rejoin the port-channel, but I was wondering is it possible to have 1 link running "on" and 1 link running "active" LACP in the same Port-Channel.

Any advice would be appreciated.

Thanks

Luke

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2 Answers 2

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Immediately: NO.

If the interface configurations differ, one or the other interface will not join the port-channel. You should never mess with the interface configuration directly -- aside from putting it in the port-channel and turning it on/off.

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You are going to need to shut this down on both sides, make your changes, then bring it back up if you want to do it safely and correctly. If you try to do this with either side up, you are likely to cause one or more ports to go into errdisable.

I'm not even sure why you need to run LACP between Cisco devices if PAgP is working today. Why do you need to send LACP control packets every second instead of every 30 seconds? PAgP fails over extremely fast, much faster than routing protocols like OSPF.

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  • Hi Ron, Im not currently running PAgP, its running EtherChannel with no negotiation. I want to use LACP as its a open standard and supported by pretty much all devices nowadays, PAgP isnt. and rate fast is a excellent way to detect uni-directional failures alot quicker and also remove a potentially degraded fibre amongst other benefits, 30 seconds is very slow to wait for the next LACPDU to be sent to confirm its neighbor is still there
    – Smithy2k3
    Mar 8, 2016 at 22:10
  • I was making a point. As it stands, your failover will be very, very fast, as fast as you can possibly make it. I'm not understanding why you want to make the change in order to run LACP fast since it really isn't doing anything for you. Not having any negotiation would be the most desired method. You should only run a negotiation protocol when it is necessary. You will not discover failures any faster than you do now.
    – Ron Maupin ♦
    Mar 8, 2016 at 22:15
  • With fibre cables we have had issues with uni-directional links not fully taking down interfaces. My thought process is whats the negative of running a negotiation protocol? It prevents configuration errors and layer 2 loops ensures both sides are configured and cabled correctly. Requires bi-directional traffic, running LACPDU's at fast rate (100bytes) a second or so will hardly cause any overhead on a link of any size and I see alot of benefits - I suppose I just dont understand why you would never want to use a negotiation protocol
    – Smithy2k3
    Mar 8, 2016 at 22:21
  • UDLD works well for detecting and fixing the problem of unidirectional fiber cables which may cause STP problems. Port channeling with negotiation can cause problems with err-disabling of ports when you make changes as you want to do. If you have an option to do something without negotiation, that is usually the best way, unless there is a compelling reason not to.
    – Ron Maupin ♦
    Mar 8, 2016 at 22:28
  • Doesn't LACP on a fast rate provide what UDLD aggressive would do? But my concern isn't just Cisco to Cisco what about problems from switch to host? UDLD wouldn't work. I suppose the topic is slightly changing. But I think I'm going to need to tear down the full Po before bringing up all links on LACP. Really good to get other people's thoughts though. Thanks
    – Smithy2k3
    Mar 8, 2016 at 22:43

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