iChat In Pictures >> You are in Folder 8_Modem:Router And it's Sub Folder Linksys Router >> Page: LAN Side DHCP
||2 Router DHCP LAN (computer) Side
This is the bottom of the previous picture in this series. It shows the LAN settings. From the router (this device), to the computers.
Again DHCP is turned off. This means the computers will have to be set to Static Routing. I did this on mine to increase security and for little other purpose as this device has UPnP and could have been left doing DHCP with UPnP enabled.
It shows that this device can change the range of it's DHCP issued IPs and the number of those IPs in the DHCP range if it is on. For your computer you can then choose, when setting Static IPs any number for this device that starts 192.168.1. The last number can be anywhere between 1 and 255 except the one the device has itself (192.168.1.1 in this case). To help avoid confusion the DHCP range normally starts at .100
A note about LAN IP ranges. There are three reserved ranges for LANs. The one this modem uses of 192.168.xxx.xxx, the one the modem in this set up uses of 10.xxx.xxx.xxx and a leesser used 172.16.xxx.xxx to 172.32.xxx.xxx
Most commonly the modem or router is the "number one" device as in 192.168.1.1 or 10.0.0.1 but in some cases the device uses an IP that appears more Out-of-the-way as this one does with 10.0.0.138 hence me saying "except the one the Device uses" above.
Why Did I Do This ?
If you leave two devices that can do DHCP actually doing it the computers on your LAN get an IP issued from both. The confusion comes from the computer only displaying one of these. In some cases you might your Airport card to join one network and the Ethernet to join another. The problem is not many applications have been written to pick one over another and iChat certainly has problems when it can "See" two Networks.
Turing DHCP Off in the Modem and setting that side of the router to Static means that that subnet now only uses two IPs the modem's own and the one the router is using. As the router is a Wireless device using specific IPs for just my computers means it is difficult for other outsiders to get on to my network.
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