Hi Franco,
I am afraid that the only way of accomplishing this is to write your own VTP packet injector in C preferably under Linux - but this might be a non-trivial task because the VTP messages are relatively complex. If you want to just "slap" additional TLVs at the end of a VTP message without even correcting its checksum then that could be relatively easy, considering the fact that you can capture a valid VTP message in Wireshark and have it exported as a constant C array. Then you could add your own TLVs at the end of this message. The resulting message would be invalid but its checksum would actually reveal it, so it is possible that the receiving switch would drop it right away without processing the internal TLVs. If you wanted the switch to actually process the TLV then it is probable that the checksum would need to be correct as well, and the mechanism for computing the MD5 checksum is not publicly known (a friend of mine has found the exact algorithm by trial-and-error, though, so I could ask him about the details).
In any case, this will require a bit of effort on your part to get it right.
Best regards,
Peter
