I've got a Site connected with RED60
The RED itself uses a single IP Subnet /31 IP Address and has 4 VLAN with /26 Subnets attached.
In the Mgmt VLAN are Sophos APX Accesspoints connecting to Central.
That setup was running up and fine for years.
In the VLAN there is a DHCP Server running on the firewall itself. It had the VLAN Interface IP set as DNS Server for DHCP Requests.
Now I did 2 things: replace the Firewall model and import the v19.5.3 config to a v20.0.1 Firewall.
Today complaint came about the APX not working and being shown offline in central while pingable on LAN.
Checking the firewall logs shows, the APX were trying to connect to wrong DNS servers an the firewall denied that.
They used Google DNS and a internal RED Interface IP that did not exist.192.168.10.65
When checking the DHCP Servers on the firewall I could see it was serving the wrong IP 192.168.10.65 as DNS Server.
After changing the IP in DHCP and rebooting the APX they are working correctly.
I checked the other 4 DHCP Servers for the RED60 and found one other that was also with wrong DNS Server while 2 were correct.
How does it come the Firewall DHCP Server changes DNS Server IP? That is a strange behavior.
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