Unable to Join Active Directory in XG Firewall

Question

Hello Everybody, 
 first of all: Sorry for my bad English - I'm German ;) 
 
 I've got a Problem with my Sophos XG Firewall (Firmware 17.5). Since November '18 my Sophos XG Firewall lost the AD Authentication and now I can't connect anymore. Can somebody help me? I checked the DNS settings and tested a lot of other Firmwares, but nothing helped... 
 I also checked the NETBIOS Domain and the FQDN - everything seems right.. 
 
 For your Information: My AD and DNS Server is located at the Synology DS 918+ (A real Server is coming in about 2 years...;); I administrate the Fire Department in my City, that's the reason for the budget infrastructure. ) 
 
 If there are additionally Information necessary, just ask me! :) 
 
 Thank you! 
 Greetings, Timo

Martin R DE · Accepted Answer

Hi Timo, 
 regards from Duisburg. 
 Please check this article - should be convenient for you as it is in german. This article solved my Synology RS815+ losing AD connection with XG after some DSM Upgrade. 
 https://www.synology-forum.de/showthread.html?98787-Active-Directory-Packet-LDAPS-SSL-Port-636-nicht-aktiviert-gel%C3%B6st 
 
 Please remember your backups prior to change config.

LuCar Toni · Answer

I think, now it is getting a little bit complicated, but lets try it. 
 Please do not post screenshots / wireshark dumps here! There can / may contain sensible data / content like passwords etc. 
 
 You should find something called "Bind request" and "bind response" in your dump. 
 https://osqa-ask.wireshark.org/questions/42719/filter-binding-request 
 The Request comes from XG to the AD. AD will respond with the bind response. 
 This Bind response contains something in wireshark, which will lead you to your answer. You can simply expand everything in the data part of Wireshark to find the answer. 
 https://ldap.com/ldap-result-code-reference/