Differences between NAT and DHCP?

nordstrodamusnordstrodamus
Posted:
in iPod + iTunes + AppleTV edited January 2014
Ok, I posted this in Digital Hub because it relates to problems I've had in gettting my replayTV to talk to my mac.



Basically, I've discovered that I can't see my replay, can't even ping it when it's connected to my home network by ethernet and my powerbook is on wireless. The airport base station is set to distribute IPs wirelessly and over the ethernet, but it apparently uses DHCP for the wireless connections and NAT for the ethernet connections.



This being the only difference I have to conclude that some difference between the two protocols (or whatever you call them) prevents interaction.



So what's the difference and is there a fix?

Comments

  • Reply 1 of 3
    stupider...likeafoxstupider...likeafox Posts: 1,618member
    I think you'll find that the Airport BaseStation is using both DHCP and NAT.



    DHCP means that each computer connected to the Airport (wireless or not) will be assigned an internal ip address. This allows them to communicate with each other but is meaningless to anyone outside the LAN.



    When someone from outside your network tries to access it, the only thing with a real ip address is the outer most link which will be either your Airport or your ADSL router.



    The Airport (or router) uses NAT to say:

    If someone hits my port x, then I'll forward it to port y on computer z. So hits on port 80 will be forwarded to the internal ip address of the machine you are using as a web server.



    So it seems unlikely that NAT has anything to do with the problem as you are communicating within a LAN.



    You say you can't ping the replayTV. What is its ip address that you are trying?. Is it set up to use DHCP and accept the ip address that the Airport dishes out?



    Edit: Have you tried a direct cable connection to take the Airport out of the picture? Trying one thing at a time would make it much easier to diagnose.
  • Reply 2 of 3
    nordstrodamusnordstrodamus Posts: 828member
    Quote:

    Originally posted by stupider...likeafox



    Edit: Have you tried a direct cable connection to take the Airport out of the picture? Trying one thing at a time would make it much easier to diagnose.



    That kind of defeats the purpose since I need another computer connected to the network in order to ping it. I can't think of any reason why the base station would do this, but it's definately the culprit.



    Now if there is just some hack to fix it.
  • Reply 3 of 3
    gargoylegargoyle Posts: 660member
    OK, what likeafox was trying to say was to test everything in order.



    1.) Connect PB to replay via cable and ping it.



    2.) Connect PB to base station (via wireless) and ping it (the base station).



    3.) Connect the replay to the base station. Then if you can (i have never seen a replay) use its menus to check it has an IP address in the same subnet as the PB. Probably 192.168.0.x



    4.) ping the replay from the PB.



    Also, NAT is not part of the equation at this stage - dont confuse yourself with it until you get your LAN working. (Unless you have the replay connected to the external port on the base staion :P )
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