[j-nsp] Need to VLAN Translate/Swap on a Trunk Interface (EX4200)

Lee Pedder lee.pedder at gmail.com
Mon Dec 23 09:15:08 EST 2013

Hi Skeeve

> I need to be able to re-write/translate/swap a VLAN on one trunk port out
> another trunk port.
> This document:
> http://kb.juniper.net/InfoCenter/index?page=content&id=KB16755&cat=JUNOS_EX&actp=LIST&smlogin=true
> Gives the process, but says ""swap" configuration can only be enabled on
> dot1q-tunneling access ports"

Yes, it is possible on access ports, whether tunneling or not, it doesn't
seem to matter. I had asked JTAC to clarify this point in their
documentation as it wasn't clear. I was using the swap function
successfully to move to a new VLAN numbering scheme on some new switches
without tunneling configured. You need to put the port you want to
translate VLANs from into access mode (even though it's trunking multiple

ge-0/0/14 {
    description "Wholesale port for VLAN translations";
    unit 0 {
        family ethernet-switching {
            port-mode access;

> The scenario is that we are taking VLANs from a wholesale provider, who are
> assigning the VLANs... we are then sending them downstream to a customer,
> but need to re-number due to VLAN conflicts.

So in this scenario, you would put the wholesale port in access mode as
above, and then you can do the translations one-by-one like this in the
VLAN stanza:

    vlan-id 506; <---- This is the VLAN ID you are running on the switch,
and will send downstream to customers
    interface {
        ge-0/0/14.0 {
            mapping {
                6 { <---- This is the VLAN ID you get from the wholesale

You don't need the "dot1q-tunneling" keyword for the "swap" to work,
although the documentation says so. One thing to note, is you must
configure a mapping for all VLANS (including those not being translated)
otherwise traffic will be dropped for them. This involves some redundant
mapping configuration to the same VLAN-ID if no translation is required, to
ensure the VLAN is trunked through.

Once the incoming translation is done, then you can trunk/access it just as
any other VLAN.

Hope this is of help, this was done on 11.4R7.5 for EX4200.


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