Wireless Point to Point Bridge / Tagged VLANS

Posted on 2014-02-06
Last Modified: 2014-02-07
I have a Customer who has contracted out some Network (Switches , Routers ) Work to a 3rd Party Vendor

They will utilize a Motorola Wireless PTP System we installed a few years ago.

3rd Party vendor has reached out to us and stated the PTP System is not passing Tagged Vlans.

I setup a test on a link 3rd party says fails to function

2 Switches
Switch A - IP: (MGMT VLAN1)
Switch B - IP: (MGMT VLAN1)

Laptop 1 - IP:
Laptop 2 - IP:

Router1 - IP:

Switch Configs (Same on Both)
Port 1 (Access) Untagged VLAN1 (Default),       Forbid VLAN2 & VLAN3
Port 2 (Access) Untagged VLAN2 ,                     Forbid VLAN1 & VLAN3
Port 3 (Access) Untagged VLAN3 ,                     Forbid VLAN1 & VLAN2
Port 8 (Trunk)    Untag VLAN1 , TAG VLAN2 , TAG VLAN3

PTP Equipment plugged into Port 8 on Both Switches
Router1 - Switch1-Port2
Laptop1 - Switch1-Port1
Laptop2 - Switch2-Port2

With This scenario , Laptop 1 cannot ping Router1 and Laptop2 , as expected
Laptop 1 can reach Mgmt/ Ping on Switch 1 and Switch 2

SO it appears that I am able to pass Tagged and Untagge VLAN across PTP

I submitted the results to 3rd Party Net Vendor ...

They knocked it down and said that unless I use different Subnet for each VLAN that it didnt prove anything ...

I guess my question is .. I didn't think VLAN would care what subnet is in use .. or am I wrong ?
Question by:bradwcampbell
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by:Craig Beck
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It is well known that some P2P wireless kit strips VLAN tags, especially Motorola kit.  IIRC there was a problem with VLAN tagging which was solved with software somewhere around 2007.

All you need to do to test is connect a device to the same port at each end and see if they can ping eachother.  That will prove whether VLAN tagging is working or not.

On each switch put port 1 in VLAN1, port 2 in VLAN2, etc...
Connnect the PTP link to port 8 (for example) and configure the trunk as you have already.
Connect a laptop to port 1 on the switch at each end and see if they can ping eachother.  As long as they are on the same subnet (forget VLAN now) they should be able to ping eachother.
Move each laptop to port 2 and test again, then move to port 3, etc, etc.
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Does the official 802.11 standard even support 802.1q tags?
I've seen them supported with non-.11 wireless kit and custom optical bridges, but not with actual wifi kit. Or it used a separate SSID/vlan.
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Craig Beck earned 500 total points
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The 802.11 standard itself only addresses the PHY and MAC layers IIRC.  That doesn't mean that the radio doesn't allow 802.1Q tags to pass over the link though.

The Cisco 1300 bridge allows 802.1Q tagging as long as the infrastructure SSID is attached to the native VLAN.

Alvarion Breeze[Access/Net] kit can pass 802.1Q tags transparently with no extra config.  These units are fully 802.11 compliant.

A lot of kit doesn't do proper 802.1Q as it doesn't really need to over the air.  A client would connect to an access point and that traffic would be segregated at the SSID level, so the AP only really needs to put that traffic onto the correct VLAN by adding the 802.1Q tag when it leaves the AP to go onto the wire.  

With PTP bridges it's a bit different and many vendors tried to implement it in different ways because it wasn't part of any 802 standard.  Motorola liked to do a lot of proprietary stuff back in their day.  I think it's just down to that but their software release notes indicate that it was supported later on.

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We went back on-site today and I appeased the 3rd party Vendor by using seperate IP subnets for each VLAN

This series PTP is the Motorola 49600  (600 Series 4.9Ghz) Public Safety

My setup on switches was as such (Attached), Please critic

Todays Test was sucessful for each laptop talking to a router on the other end of PTP link .. either on untagged VLAN or Tagged VLAN on Trunk

but I am open to any comment why i could be doing this wrong ...

Thanks again for any guidance or thoughts
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by:Craig Beck
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You didn't really need the routers.  Two laptops would have been enough.

So did you connect the router to port 1 at one end and the laptop to port 1 at the other end?

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Yes I did and vice versa with second router and laptop...

I didnt think I needed the routers two , but wanted to be able to say to 3rd party Vendor that I was passing traffic at the same time across both vlans to equipment off the router..  to do that I needed some hardware to hit
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by:Craig Beck
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Ok so as you seem to have proved that the link is passing VLAN traffic, is there an issue now?  Is the vendor still arguing that VLANs are being passed?

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No word from the vendor ..

Thanks for the review .. I just wanted to be sure that I had tested thoroughly and wasnt missing anything !

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