Posted on July 15, 2020 3:25 am
 |  Asked by JOONHWAN CHO
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I want to know how to test lacp port-priority.

I check show lacp neighbor  and  change port-pritoiry.

ex)there is port 1,2,3.

port 1,2 priority is 100, port 3 priority 3 is 1000. but  port 3 doesn’t change  standby port.

How to  change port 3 standby port ? or test it?

In advance, thanks.


Posted by prajwala an
Answered on July 15, 2020 12:38 pm

Hi Joonhwan,

Thank you for reaching us out on this platform.

The LACP Port-priority determines the ports that are placed in standby mode when hardware limitations prevent a single aggregation of all compatible ports. For eg. Every platform has a limit on the number of interfaces that can be a part of the port-channel ( you can refer to the data sheet of the relevant platform that you are using ). So if the number of interfaces configures for a port-channel is more than the limit, then the port that would go to the standby mode would be determined by the priority ( lower the priority number, higher is the priority ).

Taking an example, the 7260QX platform ( as mentioned in Data sheet ) supports 64 interfaces per port-channel. So in case we configure the 65th interface, then the port with the higher priority number would go to standby mode.In the above case since only 3 ports exist, none of them would go to standby mode since any / every platform certainly supports this number.

Additionally, I would like to let you know that the Lacp port-priority is useful when using "static fallback mode".

You can refer about the same from our eos manual in case you need anytime later ( attached is the same ).

Hope that helps. Please free to let us know if you have any further queries.



Answered on July 16, 2020 5:16 am

Thank you for your answer

I tested DCS-7280TR-48C6-R because  It has a 16 Max ports per port-channel and it is easy to test it.

I configured 1-13, 16-18 interface  are  priority 100 and 14,15 are priority 1000.

I expected result that port 14,15 are standby.

but As follow result,  interface 17,18 are standby.

please check configuration and result as follow.

I additionally change channel-group 100 mode on but  the result is same.

Thank you.


interface Port-Channel100
no switchport
ip address
port-channel lacp fallback static
interface Ethernet1
channel-group 100 mode active
lacp port-priority 100

interface Ethernet 2-13 is same configuration.

channel-group 100 mode active
lacp port-priority 100


interface Ethernet14
channel-group 100 mode active
lacp port-priority 1000
interface Ethernet15
channel-group 100 mode active
lacp port-priority 1000

interface Ethernet16
channel-group 100 mode active
lacp port-priority 100
interface Ethernet17
channel-group 100 mode active
lacp port-priority 100
interface Ethernet18
channel-group 100 mode active
lacp port-priority 100

BL-01#show port-channel 100 detailed
Port Channel Port-Channel100 (Fallback State: Monitoring):
Active Ports:
Port Time became active Protocol Mode
---------------- ------------------------ -------------- ------
Ethernet1 14:05:13 LACP Active
Ethernet2 14:05:14 LACP Active
Ethernet3 14:05:14 LACP Active
Ethernet4 14:05:14 LACP Active
Ethernet5 14:05:14 LACP Active
Ethernet6 14:05:14 LACP Active
Ethernet7 14:05:14 LACP Active
Ethernet8 14:05:14 LACP Active
Ethernet9 14:05:15 LACP Active
Ethernet10 14:05:14 LACP Active
Ethernet11 14:05:15 LACP Active
Ethernet12 14:05:19 LACP Active
Ethernet13 14:05:15 LACP Active
Ethernet14 14:05:16 LACP Active
Ethernet15 14:05:19 LACP Active
Ethernet16 14:05:15 LACP Active

Configured, but inactive ports:
Port Time became inactive Reason unconfigured
---------------- -------------------------- ----------------------------------
Ethernet17 Always Limit: too many ports in aggregate
Ethernet18 Always Limit: too many ports in aggregate



BL-01# show lacp neighbor
State: A = Active, P = Passive; S=ShortTimeout, L=LongTimeout;
G = Aggregable, I = Individual; s+=InSync, s-=OutOfSync;
C = Collecting, X = state machine expired,
D = Distributing, d = default neighbor state
| Partner
Port Status | Sys-id Port# State OperKey PortPri
---------- --------------|----------------------------- ----------- ------------- ------------- -------
Port Channel Port-Channel10:
Port Channel Port-Channel100:
Et1 Bundled | 8000,44-4c-a8-f7-58-db 1 ALGs+CD 0x0064 100
Et2 Bundled | 8000,44-4c-a8-f7-58-db 2 ALGs+CD 0x0064 100
Et3 Bundled | 8000,44-4c-a8-f7-58-db 3 ALGs+CD 0x0064 100
Et4 Bundled | 8000,44-4c-a8-f7-58-db 4 ALGs+CD 0x0064 100
Et5 Bundled | 8000,44-4c-a8-f7-58-db 5 ALGs+CD 0x0064 100
Et6 Bundled | 8000,44-4c-a8-f7-58-db 6 ALGs+CD 0x0064 100
Et7 Bundled | 8000,44-4c-a8-f7-58-db 7 ALGs+CD 0x0064 100
Et8 Bundled | 8000,44-4c-a8-f7-58-db 8 ALGs+CD 0x0064 100
Et9 Bundled | 8000,44-4c-a8-f7-58-db 9 ALGs+CD 0x0064 100
Et10 Bundled | 8000,44-4c-a8-f7-58-db 10 ALGs+CD 0x0064 100
Et11 Bundled | 8000,44-4c-a8-f7-58-db 11 ALGs+CD 0x0064 100
Et12 Bundled | 8000,44-4c-a8-f7-58-db 12 ALGs+CD 0x0064 100
Et13 Bundled | 8000,44-4c-a8-f7-58-db 13 ALGs+CD 0x0064 100
Et14 Bundled | 8000,44-4c-a8-f7-58-db 14 ALGs+CD 0x0064 1000
Et15 Bundled | 8000,44-4c-a8-f7-58-db 15 ALGs+CD 0x0064 1000
Et16 Bundled | 8000,44-4c-a8-f7-58-db 16 ALGs+CD 0x0064 100


Posted by Alla Anunitya
Answered on July 17, 2020 10:35 am

Hi Joonhwan,

Thank you for writing this!

Though you have lowered the port-priority to 100 to make Et 17 & Et18 active on the deviceA(LACP actor), if the  links are put in standby mode on the deviceB(LACP partner), in this case, the et17 & 18 will be in standby mode.

Only when both devices A&B (lacp actor and partner) put the links in an active state, then the links will become active. Else if one side of the link is active & other side is standby > links will be in standby mode.

Could you let me know if you have you made a similar change on the lacp partner on the corresponding links?

Could you please lower the port-priority on the LACP partner deviceB as well and check? 

Let me know if it works.


Anunitya A

Posted by prajwala an
Answered on July 20, 2020 5:29 pm

Hi Joonhwan,


Thank you for keeping us posted with the results. I see from your configuration that, the expected result should have been to see et14 and et15 in standby mode. As of now, I am checking internally on this and shall keep you posted with updates.

In the meanwhile could you please confirm if you configured the same priorities on individual respective links, on the other connected switch as well ?



Posted by prajwala an
Answered on July 21, 2020 7:49 am

Hi Joonhwan,

We checked this internally and confirmed that in our present implementation, the "lacp port-priority" is used only for "fallback".

The ports that will go into the standby mode is not deterministic. Apologies for the confusion earlier and please let us know if you have any further queries on this.



Answered on July 22, 2020 1:59 am

OK thank you for your check.

I will test it and my result inform you.


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