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Network Failure

I've got a problem with Snom phones behind a Sonicwall with the latest firmware SonicOS Enhanced 6.5.2.1-31n

 

The Snom phones which range from 720, 760 to 725 only purchased last month and all on 8.9.3.88 (3CX preferred version) all exhibit the same issue where calls disconnect with "Network Failure"

 

Phones from Yealink and Fanvil behind the same firewall all work fine



Best Answer

OK, here's the answer for anyone else who has this problem. 

This error pops up when using Snom phones behind a Sonicwall with 3CX hosted in The Cloud. Using an SBC on the LAN will fix the issue but it's overkill for a small site. The problem is most prevalent where the WAN interface is FTTC PPPOE and it seems to be an MTU/packet fragmentation issue - LAN MTU is 1500, FTTC MTU is 1492


The solution is to enable "Do not send ICMP Fragmentation Needed for outbound packets over the Interface MTU" in the Wan interface Advanced settings.


Hello, 


please try the solution offered by this FAQ


Best Regards

snom support team

Yup, done that, 3CX enable that by default in their templates and confirmed correct in the phone configuration.

Answer

OK, here's the answer for anyone else who has this problem. 

This error pops up when using Snom phones behind a Sonicwall with 3CX hosted in The Cloud. Using an SBC on the LAN will fix the issue but it's overkill for a small site. The problem is most prevalent where the WAN interface is FTTC PPPOE and it seems to be an MTU/packet fragmentation issue - LAN MTU is 1500, FTTC MTU is 1492


The solution is to enable "Do not send ICMP Fragmentation Needed for outbound packets over the Interface MTU" in the Wan interface Advanced settings.

Dear Michael, 


thenak you for sharing this solution. 


Best regards

snom support team

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