topic Re: "def" LACP flag in interface in ExtremeSwitching (VSP/Fabric Engine)

"def" LACP flag in interface

JoseG — Wed, 16 Sep 2026 08:46:19 GMT

Hi all.

I have a strange case here, or at least I've never seen such behaviour. I have a SMLT with LACP between two VSP-7254XTQ (8.10.3.0) and a final device.. In both VSP:

mlt 1 enable name "Device"

interface mlt 1
smlt
lacp enable key 1
flex-uni enable
exit

interface GigabitEthernet 1/1
lacp key 1 aggregation enable
lacp enable
exit

The LACP was working with no problem until someone accidentally configured "lacp key 1" in another interface, not related with this SMLT, and the SMLT went down. Then I shutted down the LACP interface (1/1) and corrected the lacp key in the other interface. After "no shut" in 1/1 the SMLT didnt go up and the log registered the next line:

LACP INFO lacpOperDisablePort: LACP operationally disabled on port 1/1 because the port's capability doesn't match key 1227 's capability.

Surprisingly, it seems that automatically the lacp key of 1/1 changed to 1227 (default lacp key) with no warning:

show lacp interface gigabitethernet 1/1

[...]

INDEX KEY SELECTED ATTACHED AGGR STATE
AGGR ID AGGR ID
-----------------------------------------------------------------------------------------------------------
1/1 1227 0 0 true act long indi def

[...]

Also I notice the "def" flag under STATE, which I don't know what means. I tried to reconfigure the lacp key:

interface gigabitethernet 1/1

shut

no lacp

lacp key 1

lacp enable

lacp key 1 aggregation enable

exit

Now:

show lacp interface gigabitethernet 1/1

[...]

====================================================================================================
Actor Oper
====================================================================================================
INDEX KEY SELECTED ATTACHED AGGR STATE
AGGR ID AGGR ID
-----------------------------------------------------------------------------------------------------------
1/1 1 0 0 true act long aggr def

====================================================================================================
Partner Admin
====================================================================================================

[...]

Now it seems ok, but when I do a "no shut"...

Log:

LACP INFO lacpOperDisablePort: LACP operationally disabled on port 1/1 because the port's capability doesn't match key 1 's capability

LACP:

show lacp interface gigabitethernet 1/1

[...]

The LACP key apparently changed to 1227 again without notice, but in the configuration:

interface GigabitEthernet 1/1
lacp key 1 aggregation enable
lacp enable
exit

Why is this happening? What the "def" flag means? How can I fix this behaviour?

Re: "def" LACP flag in interface

Michael_Morey — Wed, 16 Sep 2026 13:37:08 GMT

Jose,

It sounds like the device is simply using the default key due to the capability error you are seeing.

The log you shared:
LACP INFO lacpOperDisablePort: LACP operationally disabled on port 1/1 because the port's capability doesn't match key 1 's capability

Indicates that there is a possible VLAN mismatch on this port with the other ports in this MLT that are already up. Please see:
https://extreme-networks.my.site.com/ExtrArticleDetail?an=000059673

I suspect that as the capability did not match, VOSS defaults to the default key which is why you see the switch after you try to bring the port up.

Re: "def" LACP flag in interface

JoseG — Fri, 18 Sep 2026 11:04:17 GMT

Thanks for the hint, but I checked the VLAN assigned in the SMLT in both sides and is the same (anyway, the SMLT would had not worked before the wrong LACP configuration in that case, and it was working with no problem).

Re: "def" LACP flag in interface

CordScott — Tue, 22 Sep 2026 14:00:40 GMT

I would do an auto-sense enable then no auto-sense enable on all ports in question, including the misconfigured one. Is it possible there was a second (or more) misconfigured port with lacp key 1?

toggling auto-sense should clear everything out.

Re: "def" LACP flag in interface

craig15miller — Wed, 23 Sep 2026 10:16:38 GMT

The "def" flag in VOSS LACP stands for "Defaulted," indicating that the port has fallen back to default operational parameters because it failed to synchronize with the configured key. This behavior typically happens when rapid toggling or key changes cause a state desynchronization, forcing the operational key back to the default formula (1024 plus the interface index, e.g., 1227). To fix this, shut down the port, clear the stuck configuration by entering default lacp key, reapply lacp key 1 along with lacp key 1 aggregation enable, and then bring the interface back up with no shutdown.