RV325 Dual Wan Router with SBS2011

Posted on 2016-10-20
Last Modified: 2016-10-21
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!
Question by:intsup
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LVL 28

Accepted Solution

masnrock earned 500 total points
ID: 41853513
1) It is NOT OK to leave both modems to have the same address. I highly recommend that you configure both modems in passthrough (some refer to this as bridge) mode. That will simplify things by eliminating the need to have the modems forward ports. The only port forwarding you will have to do is on the RV325 itself. This will also prevent you from running into a scenario involving double NAT, and allow you to more easily change ISPs without changing things on the internal network. Will simplify things greatly. (If you do not configure the two modems as passthrough (or bridge), it would be as if you have 3 routers on the network: each modem, then the RV325)

2) If you configure the modems as passthrough, you won't be using DHCP service on them.

3) Any DHCP requests received on the WAN interfaces will NOT get relayed.

4) What is currently acting as the DHCP server? If modem was handling DHCP before, then let the RV325 take over that duty (you'll have because of the NAT that will be occurring). If the server was handling DHCP before, turn off DHCP on the RV325 if you want the server to continue handling it.  Otherwise, turn off DHCP on the server and make sure to leave it the DHCP service enabled on the RV325.

[noticed you accidentally did not have a #5]

6) On the LAN interface, it should have a static address. If you're using 192.168.0.x for your network devices, then it should be ... assuming both your internet connections have dynamic addresses, then I recommend you configure both WAN ports for dymanic addresses (with the correct settings for each ISP). And as I have been pointing out, you should configure each modem in passthrough mode.

7) In theory it shouldn't matter. Ideally, you would have to use the updater on the RV325. However, having the SBS2011 server continue running the Dyn updater won't hurt you either.

So I know that I've been mentioning that you should reconfigure the two modems, so here are directions for each:
Configuring the D-Link DSL-520B in Bridge Mode
Configuring the Surfboard SBG6580 in Bridge Mode

Once you've configured both of these, you'll need to restart each modem. There is a slim chance you may need to pass your ISP to break the existing DHCP lease if the internet doesn't work after rebooting the modem. But more often than not, that is not the case.

Author Comment

ID: 41854523
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!
LVL 28

Expert Comment

ID: 41854544
You would disable DHCP on the RV325. Relay would be applicable if a system on a different subnet was supposed to be handling DHCP.
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Author Comment

ID: 41854557
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!
LVL 28

Expert Comment

ID: 41854607
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

Author Comment

ID: 41854622

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