8
Creating Subnets
Subnets are groupings of computers on the same network that simplify administration. You can organize subnets any way that is useful to you. For example, you can create subnets for different groups within your organization or for different floors of a building. Once you have grouped client computers into subnets, you can configure options for all the computers in a subnet at one time instead of setting options for individual client computers. Each subnet needs a way to connect to the other subnets. A hardware device called a router typically connects subnets.
Assigning IP Addresses Dynamically
With dynamic allocation, an IP address is assigned for a limited period of time (the lease time) or until the client computer doesn’t need the IP address, whichever comes first. By using short leases, DHCP can reassign IP addresses on networks that have more computers than available IP addresses.
Addresses allocated to Virtual Private Network (VPN) clients are distributed much like DHCP addresses, but they don’t come out of the same range of addresses as DHCP. If you plan on using VPN, be sure to leave some addresses unallocated by DHCP for use by VPN. To learn more about VPN, see Chapter 5, “VPN Service,” on page 71.
Using Static IP Addresses
Static IP addresses are assigned to a computer or device once and then don’t change. You may want to assign static IP addresses to computers that must have a continuous Internet presence, such as web servers. Other devices that must be continuously available to network users, such as printers, may also benefit from static IP addresses.
Static IP addresses must be set up manually by entering the IP address on the computer or device that is assigned the address. Manually configured static IP addresses avoid possible issues certain services may have with
Don’t include Static IP address ranges in the range distributed by DHCP.
Locating the DHCP Server
When a client computer looks for a DHCP server, it broadcasts a message. If your DHCP server is on a different subnet from the client computer, you must make sure the routers that connect your subnets can forward the client broadcasts and the DHCP server responses. A relay agent or router on your network that can relay BootP communications will work for DHCP. If you don’t have a means to relay BootP communications, you must place the DHCP server on the same subnet as your client.
