problem installing Endian firewall

Please help me, Currently we have about 10 pc’s sharing internet. and We have CISCO 800 series router that connect the ADSL, to the lan Segment it connect switch throw the switch all pc’s are getting connecting. all user pc’s having 192.168.3.— range ips and gateway is 192.168.3.254

now i install the endian firewall to one PC, it must work as firewall,VPN & proxy

i made green zone ip as 192.168.3.222 then how to give red zone IP? i know that is static IP but it cant be same range

so please help me out to sort this without changing anything in router, if want i can change the internal IP sets instead of 3.– 10.– or something like that

and also please state me at present i tried Endian firewall red and green zone cables are pluged in to network switch only

I didn’t find the right solution from the internet.
References:
https://www.linuxquestions.org/questions/linux-software-2/problem-installing-endian-firewall-4175411163/

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