Why do we have to set up the switch in transparent mode when dealing with private VLANs?
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Cisco says:
You must configure VTP to transparent mode before you can create a private VLAN. Private VLANs are configured in the context of a single switch and cannot have members on other switches. Private VLANs also carry TLVs that are not known to all types of Cisco switches.
Reference: Private VLANs
Actually if you have a look at the structure of a Subset Advertisements packet in VTP v2 (used to annouce the VLANs) you won't find any option to announce a "private" VLAN. So it seems more an unsupported feature rather than a design choice.
Reference: Understanding VLAN Trunk Protocol (VTP)
At the end it seems that this feature is avaible with VTP v3
- Key Benefits of VTP Version 3
- ...
- In addition to supporting the concept of normal VLANs, VTP version 3 can transfer information regarding Private VLAN (PVLAN) structures.
Reference: VTP Version 3
Another quote:
Because VTP versions 1 and 2 do not support private VLANs, you must manually configure private VLANs on all switches in the Layer 2 network. If you do not configure the primary and secondary VLAN association in some switches in the network, the Layer 2 databases in these switches are not merged. This situation can result in unnecessary flooding of private VLAN traffic on those switches. VTP version 3 does support private VLANs, so you do not need to manually configure private VLANs on all switches in the Layer 2 network.
Reference: Private VLANs Across Multiple Switches
