My needs will be met by two patch panels with dedicated copper running between them for each port. But I'm looking at a few hundred ports and I'd rather not have to run a few hundred cables.

Unfortunately, VLANs are not an option (at least not in any configuration I'm aware of) so I am looking for some other means of trunking things together onto a single cable while ensuring they remain separate on either end. Maybe there is something similar to VLANs or maybe there is some way of wrapping one VLAN tag inside another? I'm hoping there's some sort of switch that will help me accomplish this.

Anyways, I'm looking for suggestions! I've attached my needs and constraints in both text and glorious MS Paint, below.

network doodle

The Vehicles and Computers are physically separated.

  • Vehicle A must have connectivity to Computer A. Vehicle B to Computer B, etc.
  • There must be zero connectivity between different Vehicles. (There will be collisions and routing problems)
  • There must be zero connectivity between different Computers. (Bad things will happen)
  • Subnets and masks CANNOT be changed (artifact of vehicle equipment).
  • The traffic between vehicles and computers will already have -multiple- VLAN taggings, and these VLANs will often (but not always) be the same between vehicles.

Edit: There will be multicast traffic between vehicles and computers. This traffic must not be shared with other vehicles/computers.

Edit2: The traffic between vehicles and computers is actually a mixture of VLAN-tagged and untagged traffic. i.e. a given link may contain packets for VLANs 1, 2, and 3, as well as untagged traffic.

2 Answers 2


If I understand your needs correctly, you should look into "QinQ" or 802.1ad

Basically "double-layer VLANs" or "VLAN Encapsulation" - the switches wrap incoming packets in an additional layer of VLAN going in, and unwrap them going out.

You'd need switches that support it, but they are commonly available. And you need to keep your head on straight when setting it up....

  • Wonderful! This sounds like exactly what I was looking for. Now I'll just have to keep my fingers crossed about the cost... I may mark this as the answer after a little more research.
    – Snorf1234
    Commented Oct 2, 2015 at 13:54

Have you investigated patch panels with RJ-21X connectors on the back. This allows 25-pair cables to connect to the patch panel.

You need to determine what category of cabling you wish to use. I believe you can get 25-pair Category-5E, but not Category-6 or above, as a 25-pair cable. Also, realize that with so many pairs in a single sheath, you could be subject to more crosstalk, so practical distances may be reduced. Termination tolerances will be tight, too, so be sure to get the cable installer to give you the test reports.

Private VLANs are a way to prevent ports in a VLAN from communicating with each other. If you have switches set up this way, you could prevent anything on one switch from communicating with anything else on the switch. Setting up a pair of switches connected together may be something to look at, too.

  • Thank you, I was not aware of the RJ-21X option. If I understand correctly, however, private vlans won't work since they subdivide VLANs, and not all of the traffic between vehicles and computers will be pre-tagged.
    – Snorf1234
    Commented Oct 1, 2015 at 21:49
  • That's still a lot of cables for hundreds of connections. Each jack needs 4 pairs, so a 25-pair cable only feeds 6 jacks of the patch panel. It can still save you 6:1 on physical cables.
    – Ron Maupin
    Commented Oct 1, 2015 at 21:56

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