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RV325 Dual Wan Router with SBS2011

thanks in advance for the help!

Here is the equipment I have and your help configuring the RV325 is appreciated:

1. Cisco RV325 dual wan router  (in the box so I haven't configured anything - ports, etc yet)
2. DLink DSL-520B dsl modem (ip address configured to allow all allowed ports, including mail, to the sbserver
3. Motorola Surfboard SBG6580 cable modem ((ip address configured to allow all allowed ports, including mail, to the sbserver
4.  Small Business Server 2011 server (ip address, handles exchange ingoing and outgoing mail)

brief background:  the cable and dsl modems have the same ip address because we used to simply swap them out whenever either would lose connection and direct the SBS 2011 machine to use as the gateway.  cable modem was the primary because it's faster.  and then allow the dnsupdater on the SBS2011 machine to update our ip address to receive email on the correct modem.  about 6 months ago the cable modem had a glitch and now some phantom DHCP service is switched on which plays havoc with the SBS 2011 DHCP server.  have tried to turn it off but all settings on the cable modem for DHCP services are OFF.  

so now that we want to simplify our life without having to swap (not that we have been able to because of the cable modem DHCS server issue), we bought the RV325 to handle the internet connection automatically.

Several questions someone can answer, unless someone has already done this and has a configuration that already works...

1.     Is it ok to leave the ip addresses the same on the cable and dsl modems?  common sense says no but want to check.  
2.     if NOT ok and each modem needs a unique ip address, then do we allow DHCP service to run on them
3.     will the RV325 block any incoming dhcp servers or does it simply work as a switch if the DHCP server on the RV325 is turned off?
4.     on the RV325 do I turn DHCP service OFF or use the RELAY?
6.     on the RV325 do I assign an IP address?  if so, what ip address?
7.     do I turn off DYNUPDATER on the SBS2011 machine and use the dns updater in the RV325?

knowing the above will get me started and thanks for the help!

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8/22/2022 - Mon

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thank you for your input and I don't know why it didn't occur to me to do passthrough.  so I have done that and have a follow up question regarding DHCP.

the SBS2011 box is in charge of our DHCP service.  so I will make the RV325 a static ip of

however, under the RV325 DHCP options, do I completely disable it or do I use DHCP relay?   and when would I use the Remote DHCP server option?

thanks again!

You would disable DHCP on the RV325. Relay would be applicable if a system on a different subnet was supposed to be handling DHCP.

thanks again and one final question and I feel i'll be able to handle it from here - the passthrough basically answered all the questions btw, thanks!

port forwarding on the RV325 is different than our existing routers.

how would I port forward incoming port 2525 to internal port 25 and route it to

our email is delivered to us on port 2525 to bypass our ISP's restrictions and I need that port to go to our SBS2011 exchange on port 25.

thanks again!
Your help has saved me hundreds of hours of internet surfing.

You would have to utilize Port Address Translation to accomplish that.

You would create a service (you might name it SMTP2) that would be port 2525 on the outside and 25 inside. Then you would create a PAT rule that says to send traffic of that service to the IP of your SBS server.

Port Address Translation on RV325