TCP/IP Network Settings and Terms

If a host is NOT using DHCP, then there are at least the following settings need to be filled by yourself manually:

IP Address: 192.168.1.101

Subnet Mask: 255.255.255.0

Default Gateway: 192.168.1.1

DNS Server IP: 206.13.28.12

(The numbers above are just examples.)

IP Address, or IPv4, is a 32-bit representation of a unique ID in the TCP/IP network. It has to be unique, such that the world will reach you when sending information to this IP address. Since most of the corporate TCP/IP networks are behind the firewalls, so the corporates can define their own TCP/IP addresses. Most commonly used ones are 192.168.1.x for Class C network, and 10.10.x.x for Class B network. In general, there is no way to reach the host behind the firewall with the IP address like 192.168.1.101, since there is no public host assigned to this kind of non-routable IP addresses.

When the web browser of this host 192.168.1.101 tries to send an http request to, say, www.yahoo.com, it will do the followings:

1. The browser tries to contact the DNS server, in this case 206.13.28.12, to know what the IP of www.yahoo.com is. (But how does 192.168.1.101 know how to reach 206.13.28.12 in the first place ?)

2. The host will apply the "Mask" operation, which actually is the bit-by-bit AND operation, between the destination, which is 206.13.28.12, and the subnet mask, which is 255.255.255.0. The result is not zero. So the host knows there is no direct link between itself and the DNS Server.

3. The host will have to go to the routing table to find the best route. Eventually it finds the default route, the default gateway. The IP of the default is 192.168.1.1. Please note that the "Mask" result between the Host and the default route has to be zero.

4. The host sends a DNS query regarding "what is the IP address of www.yahoo.com" to the default gateway.

5. The default gateway eventually send the DNS query to the DNS server and get back the answer to the host. The answer is: 66.94.230.36.

6. Finally, the browser goes through step 2, 3, and 4 again to send the http Get request to www.yahoo.com, and gets the response back.

The whole process takes two round trips to the Internet just to get one home page of www.yahoo.com. In the subsequent requests to www.yahoo.com, the first round trip can be saved as the browser may use the cache value 66.94.230.36 to try first.

If you are using DHCP, you still need to have IP address, Subnet mask, Default Gateway and DNS server on the host. The difference is you don’t need to manually setup them yourself, you get them automatically when your system boots up and requests them from the DHCP Server.