I've run into flapping issues when adding a vlan if the vlan wasn't
present upstream. I don't know if this is your case, but in my case, I
had two 6500 cores each attached to the same 3750. port channels and
spanning tree in place. When I added a vlan to an interface on one
core, the spanning tree went nuts because the vlan wasn't present
everywhere it should have been. My suggestion, then, is be sure the
vlan you're adding is everywhere it needs to me. I would have sworn I
had my vlan everywhere, but I didn't, I'd missed in 1 place, so give it
a look......
-Rick
Jared Gillis wrote:
Hi all,
I just ran into a strange problem on a 3750ME. I've got two gig ports in an
active LACP port-channel looking like this:
interface GigabitEthernet1/0/1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 101,102,400,664,1000-2999
switchport mode trunk
speed 1000
duplex full
channel-group 1 mode active
end
interface GigabitEthernet1/0/2
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 101,102,400,664,1000-2999
switchport mode trunk
speed 1000
duplex full
channel-group 1 mode active
end
interface Port-channel1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 101,102,400,664,1000-2999
switchport mode trunk
end
When I added vlan 400 to the trunk allowed vlan list, one of the underlying gig ports flapped, which caused the port-channel to flap as well.
Jan 7 12:09:27.647 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to down
Jan 7 12:09:27.656 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Port-channel1, changed state to down
Jan 7 12:09:28.654 PST: %LINK-3-UPDOWN: Interface Port-channel1, changed state
to down
Jan 7 12:09:31.464 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface
GigabitEthernet1/0/1, changed state to up
Jan 7 12:09:32.454 PST: %LINK-3-UPDOWN: Interface Port-channel1, changed state
to up
Jan 7 12:09:33.461 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Port-channel1, changed state to up
Jan 7 12:09:48.745 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Vlan400, changed state to up
This definitely seems like something that should not happen. I'm running Cisco
IOS Software, C3750ME Software (C3750ME-I5K91-M), Version 12.2(46)SE, RELEASE
SOFTWARE (fc2).
Any thoughts on what I should be checking?
--Jared
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Rick Coloccia, Jr.
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State University of NY College at Geneseo
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