This page is a simple introduction to the concepts involved in understanding local networks. If you are looking for information about how your internet connection fits in with your network, please see Public IP addresses.

IP addresses

Each device connected to the network is given a unique identifier, known as the IP address of the device. An IP address consists of four numbers separated by decimal points. The following are all examples of valid IP addresses:

10.0.1.1
192.168.1.100
254.254.254.254

It is not possible for more than one device to share the same IP address.

Ports

When network devices send messages to each other, they have to specify the port that receives the message. This is like an in-tray that helps the receiving device know what to do with the information.

By convention, port 80 is used to send and receive web pages.

Subnets

Networks can be organised by separating IP addresses into different subnets. It is only possible for a device to communicate with other devices that are on the same subnet.

The subnet is most commonly indicated by the first three parts of an IP address, leaving the fourth part free to vary. The following IP addresses are all on the same subnet:

10.0.1.1
10.0.1.2
10.0.1.200

This arrangement is described by the subnet mask "255.255.255.0".

If you have a router with DHCP turned on, a good way to work out the subnet of your local network is to set your Mac to use DHCP in the Network pane of System Preferences and then make a note of the IP address given to it by the router.

DHCP

It can be a chore to manually set unique IP addresses for each device on your network. For this reason, a technology called DHCP exists that allows IP addresses to be automatically assigned to network devices. Many devices now use this technology by default.

However, since IP addresses assigned by DHCP can change every time the device connects to the network, you should manually set the IP addresses of all network cameras, and of any Macs you wish to set up to stream video for remote monitoring.

Make sure any IP addresses that you assign manually are outside the range reserved by your router for DHCP.