Environment:
Catalyst 3750s and 3560s
Multiple data VLANs, dedicated voice VLAN
Polycom IP phones, support CDP
Questions:
1. Given a single switch port configured for both an access and voice VLAN, why is the voice VLAN not detected unless CDP is enabled on the phone? What is CDP doing exactly?
2. Right now, I have to manually configure a switch port for both a data and voice VLAN for a phone and computer to work on the same line. The phone is always placed inline between the switch and the end computer. If a switch port is configured like this, though, the computer will not communicate on the LAN without the phone present. Also, adding the voice VLAN manually is required when a phone is introduced on a working data port where a phone had never been.
Is there a way to automate addition (and removal) of the voice VLAN command on a given port? In other words, given an already configured data port, how can addition and removal of a phone be made seamless so as to require no administrative intervention? I am seeking ease of administration but am also interested in learning potential security implications of auto configuration.
3. Security consideration for CDP specifically?
4. Any other ideas about how to streamline a musical phone scenario?
Thanks!
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Thanks Chopper, but I already know the typical port configuration. This is exactly what I'm doing. And regarding CDP, for whatever reason it is required with my Polycom phones; it plainly says so in the Polycom documentation, which I only discovered when my first phone just wouldn't work.
The thrust of my question was about autoconfiguration of the voice VLAN, i.e. autosensing a phone when it is introduce on an existing data port and configuring accordingly.
Ok it sounds like the switchports need to operate in trunking mode if only one vlan is allowed to work at a time in access mode....try the following config on your switchport
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 1
switchport trunk allowed vlan 1,2
switchport mode trunk
spanning-tree portfast
1=data vlan
2=voice vlan (update to your specific environment)
Trunk links are required to pass VLAN information between switches (in your case the mini switch in the phone). Access ports belong to a single VLAN and do not provide any identifying marks on the frames that are passed between switches. Access ports also carry traffic that comes from only the VLAN assigned to the port.
So to answer your question...yes.
However, VLANs aren't going to fully protect your voice network in access mode either. If you have an intelligent attack against VoIP initiated on your Data network....the VLANs are only going to protect you against a limited number of attacks. Hence, the reason for so many security measures and various applications available for Voice networks and servers.
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by: ChopperCenturyPosted on 2008-12-02 at 11:03:12ID: 23079708
Here is a typical config for a PC and Phone to work on the same switchport....
interface FastEthernet#/#
switchport mode access
switchport voice vlan #
Also if you want to change the PC VLAN from the default, simply add the following...
switchport access vlan #
CDP has no bearing on either of these to work....CDP is just for discovery, letting you know what devices are connected to the ports.