Wireless Access

Aruba Employee

CDP "Fingerprinting" - Your Cisco phones are now FREE!

A lot of legacy Cisco phones only support Cisco's proprietary CDP protocol. For Cisco VoIP phones, one of the things that CDP provides is a mechanism to communicate a voice VLAN defined on a Cisco switch to a Cisco phone via a CDP message; once the phone receives the voice vlan message, voip packets are sent with the appropriate vlan tag to the connected switch and qos takes care of the rest. The key value here is that it eliminates the need to configure the voice vlan on each phone manually... deploy a 1000 phones and voila, no need to configure a voice vlan manually on each phone.


While such a capability is useful in principle, many legacy Cisco VoIP phone customers only realize after the fact that this only works with Cisco switches, talk about vendor lock-in... ouch!!


Today, there are standard based LLDP/LLDP-MED that allows you to accomplish the same thing that you can do with CDP with any phone or switch that supports these standards, however, what do you do if you already have a large investment in Cisco phones that only support CDP?


A number of Aruba mobility switch customers posed this challenge to us on whether we could translate anything we do with "device fingerprinting" for Cisco phones... in true Aruba fashion we went off for a few weeks and came back with "CDP fingerprinting" 


When this capability is enabled, we listen to the initial frames and if they are CDP packets we automatically detect the phone and place traffic from the voice vlan and thereby provide the same QoS services as if the phone had sent the appropriately tagged packets; before you ask, if a data device is daisy chained through the phone that device is treated differently and not placed in the voip vlan... :-)


No need to manually configure your Cisco phones or even worse immediately come up with budget to refresh them... cool, eh?


Give this feature a whirl on our mobility access switches (you will need to be running ArubaOS 7.1.3 or greater)


host) (config) #interface-profile voip-profile <profile-name>

(host) (VOIP profile "<profile-name>") #voip-mode auto-discover


We'd love to hear your thoughts on this


Aruba Employee

Re: CDP "Fingerprinting" - Your Cisco phones are now FREE!

I can verify this works great!! We have over 3000 Cisco 7940 and 7960 Cisco phones. This feature works great and as Abe says the data port on the phone works just like it did on the Cisco switches. 


One note here is that if you have manually configured the Voice VLAN you need to clear it, otherwise the phone is confised as to how to send the voice traffic.


This also works with newer models, but you can also just provision LLDP-MED for those as well.



Occasional Contributor II

Re: CDP "Fingerprinting" - Your Cisco phones are now FREE!

Is this capability available on RAP devices?


Re: CDP "Fingerprinting" - Your Cisco phones are now FREE!


Sorry for the delay responding on this but CDP Fingerprinting (aka CDP Receive Processing) is not currently available with the RAPs. However that said, you could craft a UDR based upon the OUI of your CDP phones to direct them to a particular vlan.


Best regards,



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