Routing for Internet Setup

Question

Hi all, 
 I have a Sophos SG135w which used to be for the work office, but we have moved and no longer require it. It was previously setup by the work MSP who we purchased the device from. It has been sitting idle for about 18 months now and I am going to set it up at home. I've got it working on a home license. 
 I have it connected to my modem/router which works on 192.168.20.40 on 1 interface. I have another interface configured for DHCP as I want the Sophos to control that (192.168.0.0/24). 
 Now the Sophos isn't running all DHCP yet, I have it connected on its on. When I am my desktop on 192.168.20.0/24 I can connect to 192.168.20.40. When I am connected to the Sophos on 192.168.0.0/24 I can connect to the Sophos of 192.168.0.1. 
 But, I have no internet connectivity. I suspect I need to do a route somehow? Or a DNS configure? Just not sure where I need to do any of this stuff and googling hasn't given me the answer. 
 Any tips or pointers would be great. 
 Thanks.

PhilippRusch · Answer

Hello, 
 delete that static route entry first! This is not needed. Routing is done by the correct GW setting. 
 Then, if I understand you correctly, your Modem/router has an address of 192.168.20.40. Then you cannot assign the same address to the transfer network interface of the Sophos going to that modem into direction "outside". 
 Additionally, you told the Sophos that your default GW is 192.168.20.1. If above IP 192.168.20.40 for the Modem is correct, then this GW entry is wrong. The GW IP has to be the IP of the Modem side. 
 You could either change the IP of the Sophos to something else like 192.168.20.10 and correct the GW entry to 192.168.20.40 or you change the modem IP to 192.168.20.1. 
 So it should look like: 
 Sophos - 192.168.20.10 ----- (Internet Link to router) ----- 192.168.20.40 - Modem(internal) ------ (external) ---- Internet 
 (With GW=192.168.20.40) 
 OR: 
 Sophos - 192.168.20.40------ (Internet Link to router) ------ 192.168.20.1-Modem(internal) ------ (external)------Internet 
 (With GW= 192.168.20.1)