4

Why do we have to set up the switch in transparent mode when dealing with private VLANs?

1
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
    – Ron Maupin
    Jan 6, 2021 at 2:44

1 Answer 1

5

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

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.