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B5-Series and Cisco IP phone 7942G DHCP Communication Failure

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TitleB5-Series and Cisco IP phone 7942G DHCP Communication Failure
Symptoms
  • After upgrading the firmware of a B5-Series switch from version 06.81.06.0002 to 06.81.07.0004 or superior all Cisco IP Phones of model 7942G fails to obtain configuration from DHCP server. 
  • The IP phone model 7942G successfully authenticates against a RADIUS server.
  • The expected policy role is applied to the port of the switch where the 7942 is physically connected.
B5(su)->show multiauth station port ge.1.1
Port         Address type Address
------------ ------------ -------------------
ge.1.1       mac          34-BD-C8-2D-02-0D

B5(su)->show multiauth port ge.1.1
Port          Mode         Max       Allowed    Current
                          users       users      users
------------ ------------ ---------- ---------- ----------
ge.1.1       auth-opt     4          4          1

B5(su)->show multiauth session port ge.1.1
__________________________________________
Port             | ge.1.1            Station address   | 34-BD-C8-11-22-33
Auth status      | success           Last attempt      | WED AUG 10 14:42:55 2016
Agent type       | mac               Session applied   | true
Server type      | radius            VLAN-Tunnel-Attr  | 30
Policy index     | 1                 Policy name       | CISCO-VOIP-PHONES
Session timeout  | 0                 Session duration  | 0,00:10:34
Idle timeout     | 300               Idle time         | 0,00:00:00
Termination time | Not Terminated    Terminate Action  | None

 
Environment
  • EOS
  • B5-Series
  • SecureStack
  • Firmware 06.81.07.0004
  • Firmware 06.81.08.0005
  • MAC Authentication
  • Policy
  • RADIUS
  • Cisco IP Phone 7942G
Cause
Switch drops DHCP discover/request packets sent by the Cisco IP Phone 7942G. 
Resolution
The workaround for the reported issue is to downgrade B5-Series' firmware to version 06.81.06.0002.
Additional notes
Only the Cisco IP Phones of model 7942G is known to be affected by the firmware 6.81.07 and superior.

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