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switch losing trunk config after power cycle


I have had this happen on a couple installs recently and am not clear why (but I suspect something with auto smart ports).

In the most recent example I have a SF300-28P and a SF300-52P connected via fiber on gi4 of each switch.  Config is very simple.  VLAN 100 for voice and native VLAN 1 for data.  on gig4 of each switch I did switchport trunk allowed vlan add 100

and nothing else.  Show run would result in:

interface gigabitethernet4
 spanning-tree link-type point-to-point
 macro description switch
 switchport trunk allowed vlan add 100
 !next command is internal.
 macro auto smartport dynamic_type switch


The switch lost power and all config came back except switchport trunk allowed vlan add 100 was missing and therefor IP phones on that switch went down.


I am 99.9% sure I had done copy run start before the power outage.  Assuming that is accurate is there a reason this would happen?  Should I be disabling auto smart ports on these switches?  They seem to sometimes also cause grief with IP phones for no apparent reason.


thanks in advance,



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Hey Brandon, yep, I'm

Hey Brandon, yep, I'm thinking it's the macros too. I'd just disable 'em and see how it goes.

-Tom Please mark answered for helpful posts

Yes, that is what I had to do

Yes, that is what I had to do at a couple sites to maintain trunk config though power cycle.  I was just surprised that they acted that way.  I could understand if they were different vendor's switches, but it seems this should not happen between switches of the same model and firmware.  

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Hello Brandon,Smartport

Hello Brandon,

Smartport actually tends to go off even more between just our switches because CDP will almost always identify them correctly.  Whenever it sees a switch it is going to execute that macro which should add all of the VLANs on the switch to the trunk link.

I have seen that process fail if the ports are not in trunk mode, since the macro does not include a switchport mode trunk command for some reason.

Turning smartport off is probably your best bet as you've seen, just keep in mind you can disable it on just your uplink ports and then keep using it for everything else if you wanted to.  You can do that on a port-by-port basis, or just go into the GUI and disable the switch detection options, or of course just turn it off globally.

You mentioned firmware so I'm assuming you check and update it regularly, but I would also recommend being on the latest firmware and bootcode just in case, although the macros tend not to change much between firmware versions.

Thank you for choosing Cisco,

Christopher Ebert - Advanced Network Support Engineer

Cisco Small Business Support Center

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