Discussion:
[c-nsp] What causes mac table relearning?
Mike
2018-10-17 21:32:08 UTC
Permalink
Hi,


    I have a network consisting of 3560g switches and I do not run
spanning tree in this network. I have noticed a symptom when a vlan
trunk interface goes down/up,  all mac addresses in the vlans carried by
that trunk also seem to be cleared at the same time. Im not just talking
the mac addresses on the port itself; rather, across the other switches
themselves , even for mac addresses that have no connection to the port
itself they just happen to be in one of the vlans. If I have missed
something fundamental I'd love to know but I am not aware of any lan
switching rules that would require this behavior.


Mike-

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Aaron1
2018-10-17 22:27:30 UTC
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You say you weren’t running spanning tree, but I thought topology change notification bridge PDUs caused a Mac flush, I don’t know For sure

Aaron
Hi,
I have a network consisting of 3560g switches and I do not run spanning tree in this network. I have noticed a symptom when a vlan trunk interface goes down/up, all mac addresses in the vlans carried by that trunk also seem to be cleared at the same time. Im not just talking the mac addresses on the port itself; rather, across the other switches themselves , even for mac addresses that have no connection to the port itself they just happen to be in one of the vlans. If I have missed something fundamental I'd love to know but I am not aware of any lan switching rules that would require this behavior.
Mike-
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Randy via cisco-nsp
2018-10-17 23:02:34 UTC
Permalink
Hi Mike,

L2 re-learn can happen for a lot of different reasons.
Can you please share your topology where you are seeing this behavior.
-Randy




________________________________
From: Aaron1 <***@gvtc.com>
To: Mike <mike-***@tiedyenetworks.com>
Cc: "cisco-***@puck.nether.net" <cisco-***@puck.nether.net>
Sent: Wednesday, October 17, 2018 3:28 PM
Subject: Re: [c-nsp] What causes mac table relearning?



You say you weren’t running spanning tree, but I thought topology change notification bridge PDUs caused a Mac flush, I don’t know For sure

Aaron
Hi,
I have a network consisting of 3560g switches and I do not run spanning tree in this network. I have noticed a symptom when a vlan trunk interface goes down/up, all mac addresses in the vlans carried by that trunk also seem to be cleared at the same time. Im not just talking the mac addresses on the port itself; rather, across the other switches themselves , even for mac addresses that have no connection to the port itself they just happen to be in one of the vlans. If I have missed something fundamental I'd love to know but I am not aware of any lan switching rules that would require this behavior.
Mike-
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Shaun Dombrosky
2018-10-22 16:25:30 UTC
Permalink
VTP pruning?

Shaun Dombrosky
Data Network Engineer
V: 406-541-5749
Stay connected with Blackfoot:

      



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Today's Topics:

1. What causes mac table relearning? (Mike)
2. Re: What causes mac table relearning? (Aaron1)
3. Re: What causes mac table relearning? (Randy)


----------------------------------------------------------------------

Message: 1
Date: Wed, 17 Oct 2018 14:32:08 -0700
From: Mike <mike-***@tiedyenetworks.com>
To: "cisco-***@puck.nether.net" <cisco-***@puck.nether.net>
Subject: [c-nsp] What causes mac table relearning?
Message-ID: <1e423352-4d48-449d-582b-***@tiedyenetworks.com>
Content-Type: text/plain; charset=utf-8; format=flowed

Hi,


??? I have a network consisting of 3560g switches and I do not run spanning tree in this network. I have noticed a symptom when a vlan trunk interface goes down/up,? all mac addresses in the vlans carried by that trunk also seem to be cleared at the same time. Im not just talking the mac addresses on the port itself; rather, across the other switches themselves , even for mac addresses that have no connection to the port itself they just happen to be in one of the vlans. If I have missed something fundamental I'd love to know but I am not aware of any lan switching rules that would require this behavior.


Mike-



------------------------------

Message: 2
Date: Wed, 17 Oct 2018 17:27:30 -0500
From: Aaron1 <***@gvtc.com>
To: Mike <mike-***@tiedyenetworks.com>
Cc: "cisco-***@puck.nether.net" <cisco-***@puck.nether.net>
Subject: Re: [c-nsp] What causes mac table relearning?
Message-ID: <772CDDCB-A385-45D7-AF71-***@gvtc.com>
Content-Type: text/plain; charset=utf-8

You say you weren?t running spanning tree, but I thought topology change notification bridge PDUs caused a Mac flush, I don?t know For sure

Aaron
Hi,
I have a network consisting of 3560g switches and I do not run spanning tree in this network. I have noticed a symptom when a vlan trunk interface goes down/up, all mac addresses in the vlans carried by that trunk also seem to be cleared at the same time. Im not just talking the mac addresses on the port itself; rather, across the other switches themselves , even for mac addresses that have no connection to the port itself they just happen to be in one of the vlans. If I have missed something fundamental I'd love to know but I am not aware of any lan switching rules that would require this behavior.
Mike-
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------------------------------

Message: 3
Date: Wed, 17 Oct 2018 23:02:34 +0000 (UTC)
From: Randy <***@yahoo.com>
To: Mike <mike-***@tiedyenetworks.com>
Cc: "cisco-***@puck.nether.net" <cisco-***@puck.nether.net>
Subject: Re: [c-nsp] What causes mac table relearning?
Message-ID: <***@mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8

Hi Mike,

L2 re-learn can happen for a lot of different reasons.
Can you please share your topology where you are seeing this behavior.
-Randy




________________________________
From: Aaron1 <***@gvtc.com>
To: Mike <mike-***@tiedyenetworks.com>
Cc: "cisco-***@puck.nether.net" <cisco-***@puck.nether.net>
Sent: Wednesday, October 17, 2018 3:28 PM
Subject: Re: [c-nsp] What causes mac table relearning?



You say you weren?t running spanning tree, but I thought topology change notification bridge PDUs caused a Mac flush, I don?t know For sure

Aaron
Hi,
I have a network consisting of 3560g switches and I do not run spanning tree in this network. I have noticed a symptom when a vlan trunk interface goes down/up, all mac addresses in the vlans carried by that trunk also seem to be cleared at the same time. Im not just talking the mac addresses on the port itself; rather, across the other switches themselves , even for mac addresses that have no connection to the port itself they just happen to be in one of the vlans. If I have missed something fundamental I'd love to know but I am not aware of any lan switching rules that would require this behavior.
Mike-
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Garrett Skjelstad
2018-10-22 16:55:41 UTC
Permalink
Yes, TCN is where I would start, MST is famous for this as well.
Post by Mike
Hi,
I have a network consisting of 3560g switches and I do not run
spanning tree in this network. I have noticed a symptom when a vlan
trunk interface goes down/up, all mac addresses in the vlans carried by
that trunk also seem to be cleared at the same time. Im not just talking
the mac addresses on the port itself; rather, across the other switches
themselves , even for mac addresses that have no connection to the port
itself they just happen to be in one of the vlans. If I have missed
something fundamental I'd love to know but I am not aware of any lan
switching rules that would require this behavior.
Mike-
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Nick Cutting
2018-10-22 17:04:32 UTC
Permalink
If it is a trunk to a server - enable "portfast trunk" so it is unaffected by TCN's.

When you say you do not run spanning tree - what do you mean by that?

You disabled it for certain VLAN's or the whole switch?

-----Original Message-----
From: cisco-nsp <cisco-nsp-***@puck.nether.net> On Behalf Of Garrett Skjelstad
Sent: Monday, October 22, 2018 12:56 PM
To: Mike <mike-***@tiedyenetworks.com>
Cc: cisco-nsp NSP <cisco-***@puck.nether.net>
Subject: Re: [c-nsp] What causes mac table relearning?

This message originates from outside of your organisation.

Yes, TCN is where I would start, MST is famous for this as well.
Post by Mike
Hi,
I have a network consisting of 3560g switches and I do not run
spanning tree in this network. I have noticed a symptom when a vlan
trunk interface goes down/up, all mac addresses in the vlans carried
by that trunk also seem to be cleared at the same time. Im not just
talking the mac addresses on the port itself; rather, across the other
switches themselves , even for mac addresses that have no connection
to the port itself they just happen to be in one of the vlans. If I
have missed something fundamental I'd love to know but I am not aware
of any lan switching rules that would require this behavior.
Mike-
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