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I have read the manual and could find no word on this, so I'm asking here.

I have a couple Macs on a wireless network, this router model: http://homesupport.cisco.com/en-us/wireless/lbc/WRT54GL

Now, since we've set up VNC and SSH to these work Macs from home, we would like our work Macs to keep the same local IP addresses, in order for port forwarding to function correctly. This means we cannot allow DHCP to change the IP addresses of the devices, but we would still like it to add a new device when it comes along automatically, and give it its own IP.

How do we set this up, and do I need to change the settings of System Preferences -> Network -> Advanced -> TCP/IP as well? I cannot figure out what DHCP with Manual means for the life of me, and non airport extreme related topics are really scarce.

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I don't think you want DHCP. The D is for dynamic. Other than that, I can't help you, but perhaps the people on serverfault can (flagged to move) –  soandos May 31 '11 at 7:57
    
Thanks. I have the option to define a specific range for the DHCP to use, but I do not know where to go from there as far as setting up statics for the machines that are already connected goes. –  Swader May 31 '11 at 8:01

2 Answers 2

up vote 4 down vote accepted

There are two possibilities I know of:

  1. Prevent DHCP from assigning a subset of IP addresses in your subnet, and use those for machines that need static addresses.
  2. Configure your DHCP server to assign static addresses for particular computers.

Both options require configuration of your DHCP server, but standard home network routers often only allow the first.

In your router's "Network Address Server Settings (DHCP)" section, set the starting address to "100". This will tell your router to only assign addresses between 192.168.1.100 and 192.168.1.254 (or whatever your first three octets are, perhaps 10.0.0.X).

Then, on the computers you want to have static addresses, go into Network → Advanced → TCP/IP and assign the address manually. Put in an IP address lower than 100, such as 192.168.1.99, a subnet mask of 255.255.255.0, and a router address of 192.168.1.1 (assuming this is the address of your router). Then save your settings, and this Mac will now always have the same address.

You will have to be careful not to assign two computers the same IP address, or they will conflict with each other.

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As a corollary to this point: on any Macintosh, if you set them up to use a static IP (I will assume you know how), they will not make a DHCP request. As a result, your DHCP server will not try to assign them an IP address through DHCP. Thus, your DHCP server cannot 'take away' their IP address. Just a point worth noting, although @Stephen Jennings has the best setup. –  Lukasa May 31 '11 at 8:46
    
Awesome, after setting TCP/IP to DHCP with Manual, it worked. (purely manual did not) Thanks! –  Swader May 31 '11 at 9:13

Find a new router that supports Static DHCP assignment. Assuming any of your machines are laptop(s), configuring the computer itself may have issue attempting to connect to off-site networks.

Using ea. machine's MAC (the network card's "serial number"), quite a few routers support the ability to ensure that machine gets the same IP when it connects to the network.

Even cheap routers can be found with this ability (eg. "Trenda" brand). If you're up to it, your current router should be support by the DD-WRT router firmware ("Services" > "Services").

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Thanks for the hint, but I only need to connect to desktop Macs. The setup that was suggested above worked perfectly to achieve this. –  Swader May 31 '11 at 10:07

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