[c-nsp] VTP Pruning

[MADMAN]

Bruce Pinsky wrote:

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> Dave Temkin wrote:
> | Does anyone have a pointer to a doc that shows *how* VTP Pruning works?  I
> | definitely know *what* it does, but none of the docs say how it determines
> | whether or not a VLAN is in use...
> |
> 
> I haven't found a public one that I can point you at.
> 
> | I had an issue years ago where even if there was an active port in a
> | VLAN, it got pruned because the CAM entry fell out after awhile.  This
> | broke things because it was in a one-way broadcast type environment
> | (market data).  The general understanding is that if a port is active in
> | that VLAN that it shouldn't be pruned....  But as I just stated, that
> | wasn't the case in the past - and I'm not sure if that was a bug or if it
> | was how it was intended to work....

   One thing VTP pruning does not do is keep a VLAN from being announced 
at all.  While beta testing the HWIC I mentioned this would be nice 
since the HWIC and other low end switches supports a limited number of 
spanning tree instances.  When you connect a trunk you get an error 
message for every STP instance over the alloted max.

   Dave
> |
> 
> According to the specs I've read, the pruning function is only notified of
> the following events for local VLAN access ports:
> 
> - - Link state change of an access port
> - - Port state change of an access port (i.e. admin status)
> - - STP forwarding state change of a VLAN on access ports
> - - VLAN membership change of an access port
> - - Management VLAN changes
> 
> So having a valid CAM entry on a port in a VLAN does not appear to be one
> of the criteria for considering that a VLAN is "active".
> 
> - --
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> bep
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-- 
David Madland
CCIE# 2016
Sr. Network Engineer
Qwest Communications
612-664-3367

"Emotion should reflect reason not guide it"