> Source: [sk166340](https://support.checkpoint.com/results/sk/sk166340)

# sk166340 - Skype for Business or Yealink calls fail after 8 seconds when SecureXL is active

| Property | Value |
|----------|-------|
| Solution ID | sk166340 |
| Date Created | 2020-04-27 |
| Last Modified | 2021-01-11 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R82.10, R82, R81.20 |

## 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

This solution requires authentication. Please log in to view the full solution.

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