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Skype for Business or Yealink calls fail after 8 seconds when SecureXL is active Technical Level
Symptoms
  • STUN protocol (3478-3481/UDP) traffic to a Microsoft-owned IP range is dropped on an accept rule for Skype for Business or Yealink traffic
  • Kernel debug shows the following messages for the STUN traffic being dropped:
    [SID: XXXXXXXXX] [WARNING]: network_classifiers_domain_handle_post_syn_context: IP resolving for ip xxx.xxx.xxx.xxx is in progress (for 0 seconds), drop connections with this IP until resolving is finished;
    [SID: XXXXXXXXX] {module} [WARNING]: cmik_loader_fw_context_match_cb: CMI APP 20 returned drop/reject. action is 1;
    cmik_loader_fw_context_match_cb: CMI APP 20([Invalid]) returned action is 1([Drop]);
  • Gateway's reverse lookup of the Microsoft-owned IP address returns "No such name".
Cause

Reverse DNS lookup for one or more Microsoft-owned IP addresses fail, so CMI drops the connections to those IP addresses until it is able to resolve the IP address to a domain name.


Solution
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