2.3 Assigning IP Addresses

Basics​

IP addresses can be assigned dynamically by a DHCP server (see the DHCP section later) or they can be assigned manually. When you assign IP addresses manually, they are static IP addresses, meaning that IP addresses that you assign to these devices do not change. This is unlike IP addresses that are assigned dynamically by a DHCP server as users sign into and log off of your network.

You should know the following terms:

  • Static address
  • Dynamic address
  • Default gateway

Static addresses are useful for devices whose addresses should not change, like printers, servers, security cameras, or network management devices. These latter devices include switches, routers, and controllers.

To configure a static address, you will need to know the default gateway, IP address, subnet mask, and optionally the DNS server address. It’s very important that static addresses are not duplicated as no two hosts can use the same IP address. Be sure to document all of the static addresses you are using on your network. Accurate documentation is a critical practice you should follow so that you don’t cause networking issues by duplicating addresses.

Default Gateway

The default gateway is the entrance and exit point of a local network. It is truly like a gateway that allows network traffic to either enter or leave your network. When devices are on the same network, they can transfer information directly, like when you want to send a file to a printer on your network. If you want to send information to a device outside of your network, your device will send it to the default gateway that will then route the information towards your desired host. The functionality of a default gateway is most often handled by a router, but there are other devices that can provide this functionality. Your default gateway is identified by the IP address of a port on that device.

You have a default gateway from your network out to your ISP or other connection to the Internet. If you have created subnets on your network, each subnet also has a default gateway. Each subnet will be represented by a different IP address on its own port on the default gateway.

By “default,” if the data packets have to leave your network, the router is the device the data packets are sent to before it leaves your network.

Documentation

The importance of accurately documenting your network and settings has been mentioned several times. So far, having a network map of your cabling and record of static IP addresses has been mentioned. There are a number of additional parameters that you should have accurate documentation for, as well as some that can make your job easier but may not be required documentation.

From an IP standpoint, you should document your entire IP scheme. The majority of this will be IP addresses that have been statically assigned. If your network has multiple scopes, you should document which devices those are assigned to and the scope options that are being delivered. List which devices the IP helpers are configured on, and list both private and public IP address assigned to your network. Whether you do that now or shortly after reviewing this information is up to you, but these would likely be minimal documentation you should have easy access to.
 

Here are additional resources you may find useful:

Complete the following task or self-assessment:

Read this article by Kevin Dooley for Auvik, Network Documentation Best Practices: What to Create & Why, which reviews documentation considerations and breaks them out as critical, useful, or nice to have.

Begin determining 

  • what would be considered critical documentation you need for your network,
  • if each item on your list is available or not available,
  • if it is not available, determine a plan to generate it.

As Dooley notes, it may be a combination of diagrams, tables, and documents. You can determine which tools are best for you to generate this information. 

Consider repeating this exercise for "useful" documentation.