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Unable to connect to Skype application using port 5061 with pre-defined TCP service Technical Level
Symptoms
  • Unable to connect the Skype application when the predefined TCP TLS service port 5061 is defined in the security policy rule.
  • SmartView Tracker logs shows the traffic is allowed, but Skype fails to sign in (stuck at "Contacting server and signing in").
  • There are no kernel drops found on the Security Gateway.
  • Packet captures shows that 3-way handshake happening along with the data transmission.
    There is bidirectional traffic, going all the way through the Security Gateway to server and back, however unable to login to the Skype application.
Cause

5061 is defined for SIP over TLS services.

In the pre-defined service of SIP port 5061, there is a protocol handler, i.e protocol SIP_TCP_Proto (configured in the SmartDashboard > Service Properties > Advanced > Protocol Type).

When a packet arrives to the Security Gateway and matched on a rule with this service configured, the special code for handling SIP will take effect.


Solution
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