Point to Point

Unanswered Question
Sep 12th, 2009

I have a Point to Point setup with Cisco 1300 APs. I have the ROOT Bridge plugged into a Cisco 4500 switch and it is trunked.

On the Non-Root Bridge side I have a computer on VLAN 10 and a Cisco Phone on VLAN20.

Before we had the Root Bridge plugged into the 4500 but the port was configured for sw access vlan 10, sw voice 20. But recently we could not get the phone to connect to the vlan even when the phone is configured manually. When we bring the phone back to the network it works, so its not the phone.

Anyone have any ideals?

I have this problem too.
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Giuseppe Larosa Mon, 09/14/2009 - 04:07

Hello Oakley,

what you see is correct: the use of voice vlan is appropriate on end user ports where a phone connects to it.

The command instructs the port to provide the voice vlan-id in CDP messages exchanged with Cisco ip phone.

But to be CDP neighbor the phone has to be directly attached to the switch port.

The presence of the two AP in the middle can be compared to the introduction of switches.

so the port of C4500 has to be configured as a trunk carrying both data vlan and voice vlan.

By the way, I don't recommend to have an AP root bridge for ant vlan: the C4500 or other device in the wired infrastructure should be the root bridge for all the vlans including the two passed to the AP.

Hope to help


o.primous Mon, 09/14/2009 - 09:15

I am getting you but also confused.

The Root Bridge (AP 1300) is at HQ and it is pointed at a building down the road that has the NON-Root Bridge (AP 1300).

The AP 1300 setup is a point to point, acting like I ran a cable to connect the buildings together.

The problem I am having is I can not connent the phone or data VLANs to the c4500. I have the native VLAN talking and can connect to both the AP 1300 power injectors but the phone and data are not connecting to the network at HQ.

Are you saying that I need to configure the AP 1300 differently other then Root and Non-Root Bridge?

If so how?

I have it configured:

ssid data

vlan 10

ssid phone

vlan 20


dot11radio 0.1

encap dot1q 1 native

bridge-group 1


encap dot1q 1 native

bridge-group 1

dot11radio 0.10

encapsulation dot1q 10

bridge-group 2


encap dot1q 10

bridge-group 2


o.primous Mon, 09/14/2009 - 11:47

I have just found out that the port that the Root-Bridge AP is plugged into on the c4500 is being blocked by spanning tree.

I do not understand why since this is a building to building connection. There in not loop.

Giuseppe Larosa Mon, 09/14/2009 - 12:43

Hello Oakely,

all devices involved in this scenario wired switches and access points :

or the access points speak STP or they forward the STP BPDUs of switches they connect to with their ethernet port.

In this case the wired switch elect one port as the designated port in segment and blocks the other one:

on each lan segment only one port can be in STP forwarding state.

let's suppose that you have connected via the power injectors the APs in this way:

AP2 to port g4/2

AP1 to port g4/3

and let's suppose that AP1 and AP2 are transparent to BPDUs (let them flow over the radio link)

port gi4/3 receives better BPDUs those sent by port gi4/2 and puts itself in STP blocking state.

STP choices the best port using a hierarchuy of criteria:

lowest root bridge-id

lowest root path cost

lowest port priority

lowest port index

in this case port gi4/2 has a lowest index of port gi4/3 and so it wins the election.

Hope to help


o.primous Tue, 09/15/2009 - 07:24

Ok, I understand that. I thought that the Root Bridge and NON-Root Bridge just pretained to the AP 1300 with injection, point-to-point setup.

All I am trying to do is setup a trunk between the to buildings without running a 7 block cable from switch to switch so that VLANs can be accessed for the phone and data connection.

Can you point me in the direction on an example config or how to configure.

The only options inside dot11Radio 0 for

station-role are:







Also I enabled the trunk port so RSTP would not shut it down with "spanning-tree link-type point-to-point".

iyde Thu, 09/17/2009 - 07:42


In this context root bridge refers to wireless and _not_ Spanning Tree. In the wireless environment one AP has to be (wireless) root and the others will be non-root.

As for Spanning Tree, I fully agree that the root bridge for any VLAN will have to be a switch and in this setup the Cat4500 sounds ideal, as you suggests.

And right, the switchport connected to the root-AP will have to be trunking.


Giuseppe Larosa Thu, 09/17/2009 - 13:18

Hello Ingolf,

thanks for clarifying this point.

Original poster is complaining of seeing one port blocked on wired switch so there is an "issue" with STP (that it may be doing its job to manage L2 redundancy).

And yes our APs are connected with trunk ports.

Best Regards



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