[c-nsp] Cat 3750E w/ MAC learning disabled shutting port?

[Sascha E. Pollok]

Hi Lukas, hi Blake,

> Is it the only up port participating in that vlan?
> 
> On Fri, Apr 24, 2015 at 8:40 AM, Lukas Tribus <luky-37 at hotmail.com> wrote:
>>> Hello people,
>>>
>>> I am looking for an explanation for a strange port flap that I
>>> experienced this afternoon and out of desperation (and because I can not
>>> find an answer on Cisco, Google, you name it and I am not yet desperate
>>> enough to open a TAC case) I am posting here.
>>>
>>> Here is the situation:
>>> Catalyst 3750E has several VLANs. One VLAN has mac-learning disabled.
>>> The VLAN is tagged on one TenG interface and untagged on a GigE.
>>> The TenG interface went down due to a transmission problem. The GigE
>>> interface went Lineproto-down too. Thats weird.
>>
>> I would guess that the box connected to the GigE interface has some
>> kind of heartbeat running towards the other end of the network and
>> resets itself (or the interface) in case the communication breaks. Like a
>> "suicide-is-better-than-a-split-brain" protection?
>>
>> Seems strange for a Catalyst to drop the link in this case. Is the box
>> in a stack?

The 3750E is a 2x3750E stack. The two interfaces are on the same stack
member (Te1/0/1 is going down, Gig1/0/33 went down too). And yes,
Gig1/0/33 was the only member left in this VLAN but there is no SVI.
Plain layer 2 with MAC-learning disabled.

To make it a little more strange: the link down of Gig1/0/33 was
actually not logged on the 3750E itself. But the switch connected to
Gig1/0/33 (a 6509 SUP720) saw its link going to up/down when Te1/0/1 of
3750E went down. Do I have to make a drawing? :)

I will try to reproduce it but as these are production boxes I can not
just do as I wish.

Thanks for any ideas
Sascha