IP changes a lot

Kenny Pollock

macrumors regular
Original poster
Aug 26, 2003
219
0
Hollywood, FL
I video chat a lot on my new MacBook using iChat. I have to forward the ports for iChat to this computer, but my 192.168.2.* number changes almost everytime I'm on my computer, it's the wierdest thing. I never turn the computer off, I just close the lid, open it when I want to use it... and the IP is constantly changing. It's setup with DHCP, should I set it up manually or is there a better solution? Thanks!
 

Queso

Suspended
Mar 4, 2006
11,824
7
Do you have admin rights to whatever is throwing out the DHCP addresses? If so, you can lock down the IP address to the interface itself, so that you always get the same address when on that network.

Each interface has a 12 digit address in Hexadecimal. To get it for your MacBook, open the Terminal (it's in the Applications/Utilities folder) and type

ifconfig en0 <-- if you're using the Ethernet port

or

ifconfig en1 <-- if you're using the Airport Extreme port

In the output you'll get a line like the following

ether 00:14:51:25:2d:6e

That's the interface, or MAC, address. Look on the DHCP server and set up a "DHCP reservation" to link the interface to the IP address you always want it to receive. It should be obvious where you put the MAC number.

Note that your DHCP server may be integrated into your router. Check the manufacturer's documentation for a how-to.
 

Kenny Pollock

macrumors regular
Original poster
Aug 26, 2003
219
0
Hollywood, FL
Thanks, sounds like exactly what I need but... I can't find any setting that will allow me to do this on my Linksys router administration screen. Would you happen to know how to on my router (or if it can be done)? I did a quick Google and found that Linksys routers didn't have this feature, but I don't trust EVERYTHING I read.
 

Queso

Suspended
Mar 4, 2006
11,824
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Looks like you're right about it not supporting the feature. That leaves you with no option but to use Static IP addressing.

Assuming that the router uses the IP address, 192.168.2.1 you should configure System Prefs>>Network>>interface>>TCP/IP on your Mac as:-

IP Address - 192.168.2.2
Subnet Mask - 255.255.255.0
Router - 192.168.2.1

DNS Server - 192.168.2.1 <- unless there is already something in this box. If there is leave it alone.

Once this is done, check that you can still get both on the router and the Internet. Then set the port forwarding to 192.168.2.2 for only the service(s) you need.

NOTE: If this doesn't work, switch the Mac back to automatic addressing.
 

trainguy77

macrumors 68040
Nov 13, 2003
3,567
1
dynamicv said:
Looks like you're right about it not supporting the feature. That leaves you with no option but to use Static IP addressing.

Assuming that the router uses the IP address, 192.168.2.1 you should configure System Prefs>>Network>>interface>>TCP/IP on your Mac as:-

IP Address - 192.168.2.2
Subnet Mask - 255.255.255.0
Router - 192.168.2.1

DNS Server - 192.168.2.1 <- unless there is already something in this box. If there is leave it alone.

Once this is done, check that you can still get both on the router and the Internet. Then set the port forwarding to 192.168.2.2 for only the service(s) you need.

NOTE: If this doesn't work, switch the Mac back to automatic addressing.
You should set the IP to something like 200 so it does not get duplicated, some DHCP servers will still hand that IP out then you will have all sorts of problems, however high numbers should be handed out alot later on. Unless you have some custom setup.(which I don't think you do):rolleyes:
 

trainguy77

macrumors 68040
Nov 13, 2003
3,567
1
mkrishnan said:
If it's not too RTFM... can anyone explain how to do this (lock a MAC address to an IP address) on an AEBS?
I took a look around on mine and I don't think you can. I have done it on true DHCP servers. However it does not seem to be in AEBS. Most home routers don't have this feature.
 

mkrishnan

Moderator emeritus
Jan 9, 2004
29,777
12
Grand Rapids, MI, USA
trainguy77 said:
I took a look around on mine and I don't think you can. I have done it on true DHCP servers. However it does not seem to be in AEBS. Most home routers don't have this feature.
Okay, this was the conclusion I drew, too, but I wasn't sure. I know that you can try and do it from the client side, which is what I've done when I wanted my iMac in my DMZ.... It would be nice to have all my standard devices locked down to fixed localnet IP addresses, though.... I was hoping that the Airport Extreme Base Station was a little bit more than a standard home router and could handle this, but I guess not.
 

trainguy77

macrumors 68040
Nov 13, 2003
3,567
1
mkrishnan said:
Okay, this was the conclusion I drew, too, but I wasn't sure. I know that you can try and do it from the client side, which is what I've done when I wanted my iMac in my DMZ.... It would be nice to have all my standard devices locked down to fixed localnet IP addresses, though.... I was hoping that the Airport Extreme Base Station was a little bit more than a standard home router and could handle this, but I guess not.
Now if you wanted a real firewall you could always set up a m0n0wall http://www.m0n0.ch/wall/ but that might be to much for you. It will run on almost any PC. A 233 mhz works great! (off topic)
 

auyongtc

macrumors member
Apr 23, 2006
46
0
Simple workaround to this "lack of features" on home routers:

- Check the DHCP function on your router, to see how many IPs and starting IP address it will automatically issue out to connected clients. If it starts with x.x.x.100 and issues up to 50, the range is until x.x.x.149 then.

- If that's the case, u have from x.x.x.150 till x.x.x.254 to mess around with (assuming it's a Class C subnet that it's set to - typically 192.168.0.x or 192.168.1.x - then again, I've seen some routers default to 10.x.x.x Class A)

- With that, you can safely use say from .150 till .254 to manually assign to your computers/devices that need port mapping. Assign them in this manner:
IP Address: x.x.x.150
Netmask: 255.255.255.0 (typically)
Gateway: (router's IP - probably x.x.x.1)
DNS Server: (router's IP - probably x.x.x.1)

- Then for the computers/devices that you have manually assigned its IP, you can now add port forwarding to your heart's content.

- Anyway, as an example, most Linksys routers have a DHCP feature that works for range 192.168.1.100 - 192.168.1.150 (if it's listed as 50 addresses). It's router IP is typically 192.168.1.1, so when assigning your computers as a manual static entry, setup the addressing on the computer as:
IP Address: 192.168.1.150
Netmask: 255.255.255.0
Gateway: 192.168.1.1
DNS Server: 192.168.1.1

- For the next computer, use IP of 192.168.1.151 instead, while the other settings remain the same.

Hope that helps :)
 

Kenny Pollock

macrumors regular
Original poster
Aug 26, 2003
219
0
Hollywood, FL
Thanks for the help, manually doing it worked great, and a couple restarts have kept the IP the same and no other computers on my network are interfering yet.