Static/Dynamic IP Address On Local Networks

Published on September 3, 2022 at 11:16 pm by LEW
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Introduction

There are a variety of reasons  you might want to have static or dynamic Internet Protocol (IP) addresses on your Local Area Network (LAN). In this post I will be considering some of the reasons why to set either static or dynamic IP address.

In the modern home LAN, IP addresses are handed out by a local router, dynamically. The router is a piece of equipment you buy, or your Internet Service Provider (ISP) provides.

However there are a few of us out there who are crazy enough to attempt home brewed router setups (which is not as crazy as it sounds, as home brewed routers tend to out perform their consumer counterparts at a given price point).

IP addresses handed out by a router can change from time to time. There are cases, servers being the primary one, where one does not want an IP address that can change, a static address. Or one could just be a serious control freak and want to assign all IP addresses themselves.

Regardless there are reasons for both dynamic (changeable) and Static (never change) IP addresses.

In the following sections I will discuss a little history, the dynamic method of stetting an IP address, and two general methods of setting a static IP address.

Boring Historical Stuff

Between 1969, when the first connection across ARPA net (predecessor to today’s Internet) occurred, until 1984 there was no dynamic way to assign an IP address. So everything was done manually.

Reverse Address resolution Protocol (RARP RFC 903) was proposed in 1984 to allow a semi-dynamic way of assigning IP addresses.

This was followed up in 1985 by the Bootstrap Protocol (BOOTP, RFC 951), which improved on RARP.

Dynamic Host Configuration Protocol (DHCP) was based on BOOTP and made its first appearance in 1993 (RFC 1531 and RFC1541). In 1997 there where some small changes to DHCP (RFC 2131), which is the current standard for IPv4 networks.

Dynamic Addresses

Before talking about static IP addresses, I want to discuss how one gets a dynamic IP address on ones LAN.

To acquire a IP address via DHCP, you need a DHCP server running on your network. Every router I have ever owned has had a DHCP server built in. There are also several open source DHCP server programs out there that one can install on almost any computer. By far the most common way to use DHCP is via a consumer router.

There is a multi step process for a client (desktop/laptop/phone/whatever) to get a DHCP address. From a high level, skipping over the really technical stuff, the process is;

There is obviously a lot of behind the scene stuff going on here. From a high level again, the client gets a lease for a certain time period, after which it is possible the IP address can change.

The DHCP server associates the IP address with the Clients Media Access Control (MAC) address, which generally does not change. The MAC address is a unique identifier associated with the clients network hardware, usually assigned by the manufacturer. If you have multiple network interfaces you will have multiple MAC addresses.

On most devices you can find your MAC address in either the system information display, or the network information display. It will vary from device to device depending on Operating System (OS), and manufacturer.

Using DHCP

In most modern systems DHCP is setup and functioning out of the box. Assuming you are using a consumer router, it will have a web interface that you can point a browser at.

On most modern routers, the default information for accessing this interface is written on the router information tag. Otherwise it will be in your owners manual, or you have to look it up on line. To access your routers interface, your computer will need to be connected to the router LAN (in most cases you will be unable to access a routers interface through WiFi). In addition you will need the default IP address (for example 192.168.1.1), the default user name (for example admin), and the default password. In some cases you might have a Uniform Resource Locator (URL) instead of an IP address (something like like www.routerlogin.net).

Once you log into the web interface, DHCP is usually listed under LAN or Advanced Settings, depending on make and model of your router. Once you find it, you will see a range of IP addresses assigned to DHCP. Continuing the above example if your router IP address is 192.168.1.1, then the range of addresses might be 192.168.1.2 to 192.168.1.254.

If you are going to be running anything that requires a fixed IP address, I would suggest modifying the DHCP rang to something like 192.168.1.100 to 192.168.1.254. This leaves you a large number of potential static IP addresses. Just for the record, if you have two devices with the same IP address, that is a bad thing for your LAN, and should be avoided.

Your router should also have the option to totally disable DHCP, if you want everything to have a static IP address.

Two Methods of Setting a Static IP Address

Method 1: Most routers that are capable of DHCP, also have an option to assign a specific IP address to a specific MAC address. Because of the variation in router software, it is not possible to specify what to specifically look for, or where it will be located in the web interface. It might require a little research to locate the function.

As an example, on most NETGEAR routers it is located under Advanced > Setup > LAN Setup. On many TP-Link routers it is located under Advanced > IP & MAC bindings.

Once you find it, you use the add function to enter an IP address and the related MAC address. Once done, you apply/save. Then from that point forward, what ever device has that MAC address will get the IP address you specified.

Method 2: Most OS’s have a method to specify a specific IP address, either via a GUI or from the command line. When this is done, the device simply announces itself on the LAN, and what IP address it will be using. This works fine as long as you do not duplicate IP addresses between multiple devices.

Note that no two OS’s are going to handle theses settings in the same way. This is another case where some research will be required.

Pros and Cons: Method 1 has the advantage of placing all static IP addresses in one spot. And because your router is assigning them, you should not have a IP conflict with DHCP dynamic assigned addresses. On the down side, if you reset/replace your router, you have to enter everything again.

Method 2 has the advantage that the static IP address is set at the device, and is not dependent on the router. However you need to keep track of what device has what address, and also what addresses are being used for DHCP by the router.

Conclusion

Assigning dynamic IP addresses in ones LAN is probably all most people will ever need, and it should work right out of the box. Letting your router handle IP address assignment means you do not have to assign IP addresses to every computer, cell phone, smart TV, streaming box, or gaming console. And this is perfectly fine for most people.

However for those that do need to assign static IP addresses to devices, we took a high level view at the two methods for doing it.

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