skype for business issues

[Shahar_Grober]

Hi,

I am facing an issue where VOIP calls from our Polycom device to Skype for business online are dropped after about 1 minute. 

The drops are one-way (incoming voice) which looks like the incoming SIP traffic is dropped. 

The topology is quite simple: 

Polycom --> CP GW --> Internet --> Skype for Business online 

some insights:

1. the problem doesn't occur when connecting the Polycom directly to the internet via a hotspot. so it is a Check point issue 

2. issue still occurs when disabling SecureXL so it is not a SXL issue 

3. Hide NAT changes source port for SIP over UDP IP is checked in inspection settings 

4. No IPS drops on VOIP. The Polycom IP is excluded from IPS and all inspection settings 

5. we see incoming connections from the Skype for business online IP range are blocked by the stealth rule 

the last point made me think that it might be a NAT issue with SIP ports range (outgoing connections are NATed but incoming connections are not recognized by the firewall as part of the same connection)

I see the following drops coming from Skype for business online IP range to the GW external IP address 

My questions are:

Are there any best practices to configure Skype for business with Check Point 

What is the recommendation for NAT with SIP?

Any insights on how to solve this issue