How does Pruning works

Unanswered Question
Peter Paluch Wed, 10/21/2009 - 02:57


The VTP Pruning is made by switches periodically (every 6 seconds or so) sending the VTP Join messages. Each of these messages contains a bit map in which the bit on i-th position signifies whether the VLAN number "i" is active on that switch. If a switch sends a VTP Join message to its neighbor having the i-th bit in the bit map set to 1, then that VLAN is active. If that bit is set to 0 then the VLAN is inactive and should be pruned. Simple, even naive, but working.

Best regards,


Peter Paluch Wed, 10/21/2009 - 10:47

Hello Neo,

You may want to read this URL for some information regarding the VTP:

However, regarding the VTP Join messages, there is no public information about it - at least I could not find any. The info I have posted earlier comes from my own small sniffing and reverse-engineering of the VTP traffic.

Best regards,



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