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  1. #1

    Bidirectional NAT

    Hello All,
    I have configured a NAT box with a Linksys wireless router in my home. Currently I am able to access the outside web from the internel network, and I want to do the same from outside. For example, to access a database server present in the internal network.

    I came across the concept of Birectional NAT and more specifically DNS_ALG on the internet while searching on the topic.

    Can anyone guide me in configuring the same. Any tips or directions for setting up will be of great help.

    Thank you,

  2. #2
    Linux Engineer
    Join Date
    Apr 2005
    Buenos Aires, Argentina
    908've got to configure your router so it forwards port 80 to the machine that is running the webserver.
    "All the drugs in this world won\'t save you from yourself"

  3. #3
    Hello Serz,
    Thank you for your reply. I think I was not complete while describing the problem

    I had a post (say, POST A)recently on this forum that illustrates my current network configuration.
    POST A=

    The problem in POST A is resolved now when I corrected the resolv.conf file (It had an entry "search localdomain". The problem was solved when I removed it and I am now able to access the internet from COMPUTER 1 as required in POST A).

    Now, I am planning to run a database server on COMPUTER 1(refer POST A). I need a solution to access this server (COMPUTER 1) from the outside world.
    I am able to access this COMPUTER 1 from the internal network. I understand that there is some kind of Bidirectional NAT involved but not sure how to proceed.

    I hope my problem description is more clear now.

    Please let me know, if I need to change any settings.


  4. $spacer_open
  5. #4
    Super Moderator Roxoff's Avatar
    Join Date
    Aug 2005
    Nottingham, England
    The solution here is still port forwarding. You either need to forward the database's connection ports from the router to the machine inside the lan (to its private-range ip address) or put a web-server on the database machine and provide web pages that allow the database to be viewed, and forward (as serz says) port 80.

    The alternative would be to put the machine outside the firewall (or into some kind of DMZ) and lock it down using its own security systems. You'd need an additional IP address from your ISP to do this, though.
    Linux user #126863 - see

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