Two networking questions

[JohnE]

I have two networking questions (both unrelated).

1) From my limited understanding of networking, I gather that one PC on the network is usually set up to dish out IP addresses, whereas the others are all set to obtain an IP address automatically (there's a special name for the IP address server - but I can't remember what it is). Here's question 1 - what are the rules for 'assigning' this special address server? I've noticed that certain IP addresses seem to configure themselves as a server automatically. For example, 169.254.0.1 works as an address server whereas 169.254.0.2 doesn't. Similarly 192.168.0.1 works but 192.169.0.1 doesn't. What are the actual rules?

2) I've noticed that a lot of new computers have two onboard LANs (often a Gigabit LAN and a 10/100). Is this just so you can connect the PC to either type of network or could such a PC be used as a 'bridge' between two otherwise unconnected networks? If so, could one PC be a member of 2 workgroups or would this only be possible with domains? (I'm thinking of using a PC for just this purpose - to act as a link between 2 unconnected networks - so I'm just trying to find out what would be involved).

[Uranium-235]

for the first question

The server on the lan that assigns IP addresses is called the DHCP (dynamic host configuration protocol) server. The 169 addressed are generally assigned if a computer can't get an address from a dhcp server. This is called APIPA (Automatic Private IP Addressing). The 192 addresses are considered 'private' addresses used in most common ethernet tcp/ip networks. If you do have a dhcp server, the network card on it that hooks the server to the rest of the network is assigned a static IP address, and most of the time, it's 192.168.0.1 by default, and the server will automatically assign IP addressed to any computer on the network that requests it starting after that address (Next in line will be 192.168.0.2). I don't know why 169.254.0.2 dosen't work, but the reason why 192.169.0.1 is because 192.168 is the network portion of the Class-B address used for private assignment (mentioned above), and that ranges all the way to 192.168.254.254, so 192.169, goes beyond the addressing scheme. However In larger netowrks (that has more computers then the default private IP addressing can fill) the DHCP server is configured to dish out whole lot more addresses, and it generally isn't configured for the 192.168 scheme.

for the second question. There can be many reasons why a computer has 2 nics. You might want to have one behind a firewall, and one with a direct connection to the net (to allow other compuers to connect to it). Or yes, it can be used to route a connection (one nic hooked to the internet, and one hooked to a network device that all your other computers are hooked to, the software on the computer can be used to route packets between the two network devices. As far as I know with Windows 2000/XP, you can only be a part of one workgroup, or domain. I think Windows XP can bridge two network connections

[JohnE]

Thnaks for the info. It was really very useful and has helped me to understand this complex area a bit better. I know a lot more now than I did when I asked the questions...

[Omega]

P.S. The other private IP ranges that will work (like 192.168.x.x) are 172.16-31.x.x and 10.x.x.x.

And yes, having two NICs is useful for various reasons. I have one computer acting as a router for my home network (one NIC connected to internet, one connected to my LAN, acting as a DHCP server), and at work, I have a computer hooked to the main corporate LAN, and another NIC hooked to a private server/testing LAN. (As a side note, the main LAN is on a 192.168.1.x network, and the testing lan is on a 10.0.0.x network).