Cat3560cx device-sensor DHCP info overwritten with PC and IP phone

[andrew.butterworth]

I have a working configuration with data/voice switchports and IBNS 2.0 dot1x/MAB.  I have enabled the device classifier and everything looks OK.  Running the command 'show device classifier attached detailed' shows what I'm expecting apart from on interfaces where a PC is piggy-backed onto an IP phone.  It seems the device-sensor cache for DHCP is removed for the attached IP phone when a PC connects.  Running the command 'show device-sensor cache interface x/x/x' has a section for each attached device.  The PC shows DHCP & LLDP information. The IP phone (Polycom) just shows LLDP information.  If I have an interface with just an IP phone attached, the device-sensor information shows DHCP for the phone as well.  If I leave the PC connected and a renew of the DHCP lease happens on the IP phone then it updates and removes the DHCP sensor information for the PC.

I'm guessing as the DHCP packets are infrequent and when new DHCP information is snooped it refreshes the device-sensor cache DHCP information. Is this the desired behaviour or is this another bug?  LLDP packets are much more frequent, but these don't seem to cause removal of the others device-sensor cache information.

This is the config

device-sensor filter-list lldp list lldp_list
 tlv name chassis-id
 tlv name system-name
 tlv name system-description
 tlv name system-capabilities
device-sensor filter-list cdp list cdp_list
 tlv name device-name
 tlv name address-type
 tlv name capabilities-type
 tlv name version-type
 tlv name platform-type
device-sensor filter-list dhcp list dhcp_list
 option name host-name
 option name requested-address
 option name parameter-request-list
 option name class-identifier
 option name v-i-vendor-class
device-sensor filter-spec dhcp include list dhcp_list
device-sensor filter-spec lldp include list lldp_list
device-sensor filter-spec cdp include list cdp_list
device-sensor notify all-changes

Catalyst 3560CX IOS 15.2.7(E11).

[balaji.bandi]

Is this issue only with Polycom ?

how about when you remove classifier is that works as expected , Like voice and Data port ?

[andrew.butterworth]

The issue is seen with any type of IP Phone with the option to piggy-back a device off it - I have Cisco, Polycom and Mitel devices, but the issue is there regardless of the type as its a DHCP snooping/device classifier issue.  Functionality wise, everything is working fine.  It's just the output from the commands 'show device classifier attached' and show device-sensor cache interface x/x/x' don't have DHCP information for the IP phone when a PC is piggy-backed.

I've just tried it with a Catalyst 3650 running IOS-XE 16.12.12 and the behaviour is the same - i.e. the DHCP information for the IP phone is removed once the PC is connected and leases a DHCP address.

Ultimately what you see is on an interface connected to just a Polycom IP phone, the device classifier uses the DHCP snooped information and the LLDP advertisements, so it correctly classifies it as a "Polycom VVX 150" (in this case). On an interface with a PC piggy-backed off the Polycom IP phone, the DHCP snooped information for the IP phone is lost once the PC connects and leases a DHCP address and the device classifier just shows "POLYCOM".