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Thread: Dynamic IP addreses

  1. #1
    Join Date
    Aug 2001

    Question Dynamic IP addreses

    Hello all,
    I have a DSL with a dynamic IP connected to a linksys router. I am trying to figure out how to setup a simple linux web server behind this setup. The IP seems to rotate between a list of 3 or 4 different numbers each time it reconnects. I poked around here but couldnt find a thread which dealt with this so I thought I would ask.

    I have looked into serviced like dynip which will solve the dynamic IP problem, but it forces me to leave a port open for them. I am woundering if there are any known problems with this type of setup? My gut feeling tells me leaving any ports open is a possible hole. Is there a way to secure it?

    I am also woundering if there is a better and safer way to link my domain to my linux box over the dynamic DSL?

    Thanks for you time

  2. #2
    I seriously doubt that the Dyndns client requires any sort of tcp port open. As it is your only solution, I wouldn't really worry too much.

  3. #3
    PHP/PostgreSQL guy
    Join Date
    Dec 2001
    Your best bet would be to do the following:

    1: on your linksys router, have it set up for static IP address (DHCP off) and obtaining the dynamic IP from your ISP. This will allow you to set up your own IP network internally.

    2: assign static IP addresses for each of your machines internally. I suggest sticking with the default that the linksys router uses, and that's 192.168.1.x (up to 253 clients). The router would be, the machines could start at, 101, 102, etc.. Also, set your windows machines gateway to as well as setting up DNS on your Windows machines (put in whatever your ISP gave you).

    3: in the port-forwarding section of your router (it's in the advanced tab I believe), have all port 80 traffic that hits your router sent to whatever IP address you assigned to your linux box.

    4: go to , register, and have a "name" set up for you and friends to use. Something like "" and have it mapped to your dynamic IP address. Downside to this is that every time your lease expires and it renews a different one, you'll have to go to this site again and change it. They do 15 minute updates so it's pretty fast. Otherwise you're all set to go.

    5: if works for you, please donate (as I've done) to help support the services they provide for free.

    Hope this helps.
    We the willing, led by the unknowing, have been doing the impossible for the ungrateful. We have done so much with so little for so long that we are now qualified to do just about anything with almost nothing.

  4. #4
    Senior Member
    Join Date
    Jul 2001
    wait a minute, if you have a router getting and IP address via DHCP from you ISP, how does leaving a port open for your dynamic DNS supplier help. If they have to connect to you, leaving a port open for them will not help at all, after your outside IP has changed....

    unless the port is left open only so that they can verify that your server is what it claims to be, after the IP change, when your server has notified them of it. or something.

    In that case, it shouldnt be too hard to set up a linux router/firewall which gets its external IP via dhcp, and allows inbound traffic on the port they require from "only"the IPaddresses that they use.

    I would need to take a couple hours to play with this, but, I am sure it is not too difficult. If I had the time it is interesting enough that I might try it just for fun...

  5. #5
    Senior Member
    Join Date
    Jan 2002
    You could also just try asking your ISP for a static IP. They may try to make you pay for that, but some will not and just assign you one. If your dynamic is only jumping between 4 different address anyways, you could probably just use one of those and not have a problem.

  6. #6
    I went with for my dhcp website hosting. You just register with them, go to tucows and get a script for auto updating, and every time you go online, within 10 min or so, the dns is updated to reflect your new ip address. Im not running through any sort of router, just a firewall/masqing box.
    Bolt actions speak louder than words.

  7. #7
    Leftie Linux Lover the_JinX's Avatar
    Join Date
    Nov 2001
    Beverwijk Netherlands
    have you tried / ??
    ASCII stupid question, get a stupid ANSI.
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