routers ip address and network config

hello i have been asked to help out with some IT needs but have limited equipment making this difficult at the moment

there network is set up like this

internet > router > security gateway > ethernet switch > server acting as dhcp server

the problem is their old IT support has dissapeared and they do not know the username, passwords or any ip address details of either the router or the security gateway.

if i connect to the router via ethernet it will not connect at all so i am guessing that it is not acting as DHCP and i will have to set a fixed ip for the laptop to be able to connect to it.  is there any way to find out what the routers ip address is or any advice on how i could connect to it?

the gateway has a wan port connected to the router and a lan port connected to the ethernet switch.

the plan is to replace the gateway (they have another) but without knowing what ip address to assign to the gateway it cannot connect to the router.

any suggestions or ideas on what i could do next would be greatly appreciated.

thank you kindly
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What type of router is it?  Many routers have a management port that you can connect to.  Many also have methods for resetting the password if lost.

If you know your external IP information, you should be able to determine the router IP from that.  It would be one of your available IP addresses.  Another possibility is that the router is managed by your ISP.  You may want to check on that if you are unsure.
From any of the computers on the network you can go to a command prompt and run IPCONFIG /all

This will give you the current IP configuration of the computer including the current default gateway IP, the DHCP server and the DNS.
drzackzussAuthor Commented:
the router is a Zyxel Prestige but i do not know if it is set to default settings.  

the thing is the gateway allows you to assign an ip address to the wan port and a seperate ip address to the lan port

i know what the lan port ip address is but i do not know what the wan port ip address is.  if i could find out what the wan port ip address is i could set the new gateway as that ip address and connect it to the router
The WAN IP address would be an address assigned by your ISP in most cases.  

What you may need to do is make a list of all external IP address, the internal IP addresses those map to and then replace both the router and firewall at the same time.

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drzackzussAuthor Commented:
Maytrix comment resolved the issue
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