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Port forwarding to /through a router?

Posted on 2004-11-29
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Last Modified: 2010-04-17
Would some experts  look at this and tell me if this is going to work please?
http://mvpbaseball.cc/help.jpg

Intro: I need mail from the internet , to reach my internal mail server.

Explanation:
In the diagram, I am  doing kind of a half a$$ DMZ by using two cisco routers with a back-to-back cable.  This segments the network, but makes one too many networks than I need (dont need the extra 192.168.0.0) However, this is all I have got to work with. Ideally I should be using two firewalls to create a DMZ (I know), but I dont have those yet.

Problem: I need to have internet email reach my internal mail server. I am not sure it is possible with the way I have things set up.  

Is there a way for mail sent to  dissolved@dissolvedz.com to reach my internal mail server?  Will all those NAT translations screw anything up?
Thanks
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Question by:dissolved
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7 Comments
 
LVL 9

Assisted Solution

by:rshooper76
rshooper76 earned 400 total points
ID: 12699996
As long as you setup the router to route the traffic properly you shoudl not have any problems.  It may be easier just to add another interface to one of your 2600 routers.
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Author Comment

by:dissolved
ID: 12700177
Thanks. The only thing I'm worried about is that my cable router does not really have much configurability as far as NAT is concerned. It only allows me to forward ports to hosts in the same network as itself. Will it work if I forward tcp 25 traffic to a router ?

Here's what I plan to do. Anyone, please chime in.

1. I will log in my cable router (192.168.1.1). I will then forward tcp 25 to the Cisco  router (192.168.1.40).
2. 192.168.1.40 will receive the traffic, and hopefully forward it out it's s0 interface, to router 192.168.2.1
3. 192.168.2.1 will then pass the frame to the exchange server 192.168.2.3


How does that sound?
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LVL 79

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by:
lrmoore earned 1600 total points
ID: 12701120
On your Cable router, forward TCp port 25 to 192.168.1.41
You can NAT on the router A:
  interface Ethernet 0
    ip add 192.168.1.40 255.255.255.0
    ip nat outside
  interface serial 0
    ip add 192.168.0.5 255.255.255.0
    ip nat inside
  ip nat inside source static 192.168.2.3 192.168.1.41
   ip route 192.168.2.0 255.255.255.0 192.168.0.6
   ip route 0.0.0.0 0.0.0.0 192.168.1.1

2500B
   int serial 0
     ip add 192.168.0.6 255.255.255.0
   int Eth 0
     ip add 192.168.2.1 255.255.255.0
   ip route 0.0.0.0 0.0.0.0 192.168.0.5

Done
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Author Comment

by:dissolved
ID: 12701777
Thanks a bunch lrmoore.

3 quick questions.

-Where did the IP 192.168.1.41 come from? Did you mean 192.168.1.40?

-static NAT looks similar to "port forwarding" (which is done on low end routers). Are they the same?

thanks
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LVL 79

Expert Comment

by:lrmoore
ID: 12706020
I used 192.168.1.41 because it is on the "outside" LAN, and because I can use any free IP address on the outside LAN subnet to create a static 1-1 nat to an "inside" host

Yes, static PAT is the same as port forwarding.
 static NAT:
   ip nat inside source static 192.168.2.3 12.34.56.7
static PAT (port forwarding)::
   ip nat inside source static tcp 192.168.2.3 25 12.34.56.8 25
   ip nat inside source static tcp 192.168.2.3 80 12.34.56.8 80

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Author Comment

by:dissolved
ID: 12707306
so static PAT can be used in this case if we wanted to (instead of using static NAT).  It would require one more line of configuration though?

We just use static NAT because it only requires one entry, instead of two.

with static NAT, we just need
ip nat inside source static 192.168.2.3  12.34.56.7


with static PAT we need two statements
ip nat inside source static tcp 192.168.2.3   25     12.34.56.8    25
ip nat inside rouce static tcp   192.168.2.3  80     12.34.56.8    80

Am I on track?
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LVL 79

Expert Comment

by:lrmoore
ID: 12707360
You're getting it! That's exactly right
And you can forward the www port 80 to your web server, and port 25 to your email server - they don't have to be the same box! How cool is that?
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