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laffeg
New Member
January 15, 2026
Question

DDS (Document Distribution Service) being blocked specifically on port 7789

  • January 15, 2026
  • 2 replies
  • 327 views

Hi

upgraded 60F to 7.4.9 and our client's 3rd party provider is saying all devices are getting DDS blocked

was using Web filter and SSL inspection on the outbound firewall policy

 

still same with them both turned off

I can't see it being blocked in forward traffic logs

do I need to go up to 7.6  or is there another fix ?

 

any help appreciated

 

Graeme

2 replies

AEK
SuperUser
SuperUser
January 15, 2026

Hi Graeme

You may have hit the below known issue. Try reboot and see if it helps.

 

1035490

The firewall policy works with proxy-based inspection mode on FortiGate models with 2GB RAM after an upgrade.

Workaround: After an upgrade, reboot the FortiGate.

 

In case it doesn't help, I heard (but nothing official) about some possible mtu/mss related issues following upgrade to 7.4.9.

This tech tip shows how to diagnose the issue and eventually how to fix it.

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Setting-TCP-MSS-value/ta-p/194518

Hope it helps

AEK
laffeg
laffegAuthor
New Member
January 19, 2026

reboot didn't help - realise now that the issue started before I did the firmware update

 

So question why would a Fortigate suddenly start blocking port 7789 and not show anything in the logs ?

AEK
SuperUser
SuperUser
January 19, 2026

Did the shared tech tip help?

AEK