Motorola SBG6580 NAT or Port Forwarding

I have a Motorola SBG6580 that I need to set up to allow access to our SBS Exchange Server on port 25

I have done nothing to the SBS Server.  our dsl modem died so we are trying to use our cable modem to work as a temporary fix until our replacement dsl modem arrives.  so any issues are related directly to our cable modem - and possibly Comcast.

When trying to set up Port Forwarding i'm asked for an internal IP address (no problem that's my SBS server at but also an EXTERNAL ip address

I've attached a screenshot.

what do I put in as the external ip address?  or do I leave it as  or is it the cable modem's ip address of

one other issue, when I try open port check tool website, and ask if port 25 is accessible, the open port website says no.  

thanks for your help!!
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intsupConnect With a Mentor Author Commented:
after trying different configurations, on the Motorola SBG6580 leaving the external ip as works since that is apparently the universal ip the modem uses to allow all traffic in..

thanks though.
Ian MeredithCommented:
The external IP Address is the addresses given to you by your ISP.

You can generally find this from looking in the management interface on your modem - status page....

Until you have configured this correctly you will not get a successful result with a Port checker....
Ian MeredithCommented:
Once you have configured the external IP correctly you should be right to go...
intsupAuthor Commented:
mine is the correct response.
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