Catholic Education Ministries

Introduction

All devices on a network (ie: printer, computers) need IP addresses. These are the devices' identities on the network. There are two primary methods of assigning IP addresses to devices, dynamic and static.

Dynamic - DHCP

The first is dynamic (DHCP). Using this method, each device connected to the network will ask other equipment on the network to assign it an IP address. The equipment that chooses the IP address is the DHCP server, which is usually part of the network's router.

Static - manual

The second is static (manual). Using this method, the network administrator manually types the network's TCP/IP information into each computer and maintains a list of which computers have been assigned which IP addresses.

Mixing the Two

When a network uses dynamic IP addresses, it is still desirable to have some devices use static IP addresses. For example, a file server generally needs a static IP address. In that case, you manually assign an IP address to that server (outside of the range of addresses used by the DHCP server).

There are also occasions where you want the device (ie: the principal's laptop) to think it is using a DHCP address, but yet always use the same IP address when in the school. That is the goal of this document.

Procedure

Before proceeding, you must decide what IP address you are going to assign to the principal's laptop. The IP address must be outside of the range of IP addresses currently used by the DHCP server. For example, your DHCP server uses the addresses 192.168.10.51 through 192.168.10.254, then you should use a smaller number, such as 192.168.10.21.

Identify the device's hardware address

The first major task of this procedure is to identify the device's hardware address. A hardware address is NOT the same as an IP address. The hardware address is a serial number unique the network card inside each computer. Hardware addresses are also known as...

• ethernet address
• physical address
• MAC address

1. Assuming the principal's laptop has Mac OS X, launch Network Utility
2. In the pop-up menu, select the network interface named Ethernet Interface (en0). (If the device communicates wirelessly, select en1.)
3. Take note of the hardware address. It will be similar to 00:0a:86:a8:20:59.

Configure the Static Entry in the DHCP Server

This procedure was creating on a 2002-vintage SonicWall-brand firewall/router. The procedure may vary on different routers, but the concept is the same.

1. Launch a web browser and go to your router's web-based interface. The address will look something like http://192.168.10.1/.
2. Login as the administrator.
3. In the left column, click DHCP.
4. Scroll down to the section titled Static Entries.
5. Type the desired static IP address.
6. Type the device's hardware address (or ethernet address).
7. Click Update.
8. Do not perform any other actions until the bottom of the screen reads, The configuration has been updated.

Unfortunately the router and the device (principal's laptop) do not always sychronize with the new information immediately. You may need to restart both. Here is the procedure to restart the router (on a 2002-vintage SonicWall).

1. Click Tools in the left column.
2. Click Restart SonicWall.
3. Click Yes.