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PBX u1900 Intermittent Connection

Publication Date:  2018-02-27 Views:  415 Downloads:  0

Issue Description

IP Telephony lost connectivity several times during business hours, the PBX is experiencing connection issues, it went down and loss the IP Phones 7900 connection, unable to make calls amoung extensions and incoming calls.

Alarm Information

Telephony service is down until customer power cycle the PBX, unable to perform and receive calls.

Handling Process

  1. Network Topology Requested 
  2. Wireshark Capture was requested in the switch core and IP Phone 
  3. LMT Capture while service is down 

Root Cause

1. After logs analysis of PBX, :  seems there is one device  with IP: is attacking the PBX, it keep sending register messages in a very short time: 

2. Then it trigger our PBX protection policy and start to drop the register messages, which also dropped the good normal register messages from IP phone. 


Customer validated a wrong configuration in the firewall, an invalid port was open. This was modified and issue solved after some time under monitoring.