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August 5, 2015

What is a Subnet?

When configuring IP devices such as IP cameras, NVRs, and DVRs, you need to set up IP addressing so each device can communicate with the other devices. If you don’t understand how IP addressing works, this can be a frustrating experience.

“Are You on the Same Subnet?”

You may keep hearing this question when you call a Tech Support representative. If you don’t understand what that is and why it’s important, then you have come to the correct place. A subnet refers to the IP address range that a computer ‘lives on’. Every device that is connected to a network has a unique address on that network. That device can only connect to another device that is in the same subnet or address range. To be able to see any other range of IP addresses, you must connect through a router or similar device that is performing NAT (Network Address Translation). A NAT device allows you to view other subnets, like Internet Addresses.

So, What is a Subnet?

A subnet is determined by your ‘Network ID’. Your Network ID is determined by a couple of factors:

1. Your router. Your router settings will determine the initial Network ID when you set up it’s LAN address (Local Area Network).

2. Your ‘Subnet Mask’ determines what range of addresses in your subnet your computer can see and communicate with.

Lets look at an IP address and break it down –

An IP V4 address consists of a group of 4 sets of numbers separated by a ‘dot’ or period. example =

Each number is limited to an integer between 1 and 255 – you’ll never see an address that contains a number larger than 255. If you do – it’s wrong.

Each ‘set’ of numbers is called an ‘Octet’ (from the Latin and Greek ‘octo’ meaning ‘eight’ – each number is an 8-bit value)

When you connect to a LAN (Local Area Network), the router will assign your computer an IP Address, Subnet Mask, Gateway, and DNS Server(s)

IP Address = the unique address of your computer on the LAN.

Subnet Mask = Determines what segments of your Network ID your computer can communicate with.

Gateway = Usually your router. Your router is the ‘Gateway’ to another network. (The Internet is another network = WAN (Wide Area Network)

DNS (Domain Name Service) Server = This is the engine that translates a DNS name into an IP Address. When you type in www.google.com, the DNS server translates that name to an IP Address =  (Computers use IP Addresses, not names.) The DNS Server looks at constantly updated tables to convert the name to the actual IP address so you can connect.

Your router usually performs NAT and DNS for you as well as other functions such as DHCP and IP Masquerading.

If you plug into a LAN and you get no IP Address or Gateway, etc. it usually means one of two things:

1. You do not have a good connection. (bad cable, defective port, or other hardware issue)

2. There is no DHCP server on the LAN. (Dynamic Host Control Protocol). A DHCP server automatically assigns an IP Address, Gateway, etc. to a device that gets connected to the LAN and is responsible for keeping all addresses it assigns unique between devices. The DHCP server is usually your router.

So, What Does it Mean to be “On the Same Subnet”?

Let’s say your computer has a LAN address of
Your computer has a standard Subnet Mask of
With that Subnet Mask, your computer can only see a device where the first three Octets match exactly. You could not connect to a computer or device with an address
of 192.168.0.xxx because the third Octet is different. Your computer is limited to 254 addresses that it can communicate with. (255 possible, minus your computer = 254)

The only way you can ever connect to another network is if one of those remaining 254 addresses is a Gateway performing NAT. (Network Address Translation).

Here is where the Subnet Mask is important – you can ‘unmask’ more addresses and expand your Network ID range.

With an address of – change your Subnet Mask to

This will ‘unmask’ the third Octet from your computer and open your Network ID to 192.168.xxx.xxx.

Now you can see a device with an address of 192.168.xxx.xxx (where x = any number between 1 and 255)

Here is how your Subnet Mask affects your Network ID.

IP =
Network ID = 192.168.1
Mask =
The first three octets must match for communication.

IP =
Network ID = 192.168
Mask =
The first two octets must match for communication.

IP =
Network ID = 192
Mask =
Only the first octet must match for communication.

This last subnet mask allows you to see a lot more devices than the standard mask = 254 x 254 x 254 = over 16 million devices instead of only 254.

What You Should Have Learned Here

Look at the Subnet Mask to determine your Network ID.
The number of times you see ‘255’ is the number of octets that must match in the LAN IP Addresses of your devices.
Those matching numbers are your ‘Network ID’.

This is an over simplification of Subnet Masking. It provides a very basic ‘rule of thumb’ for setting network addresses.
There are other numbers you may see on a subnet mask such as 192, 224, 240, 248, 252.

If you see these other numbers appear in your Subnet Mask, consider them a ‘red flag’.

If and when you see this, STOP what you are doing. I guarantee there will be an IT person on site that you will need to consult. Only an IT person (or Network Administrator) will be using those numbers on a LAN and you have no choice but to involve them in the process. (Unless you are an Information Technology person or Network Administrator and you understand how those other numbers can limit the usable IP addresses available on the LAN)

In short – if you see anything other than ‘255’ in your LAN subnet mask this is a strictly managed network and your chances of casually breezing through your installation have just ended.

Call the on site Network Admin for advice before you do anything else.

There are other ranges of IP Addresses that you may encounter on the LAN. Don’t be afraid! They all work the same way.
A LAN will always use what are called Private or Internal address ranges. These addresses will never be used on the Internet, they are reserved for use on the Internal LAN.


If you look at a DHCP LAN address on your computer and it does not fall within one of the private ranges shown above, there is a problem.

There is one more range of addresses you may see, but they usually indicate a network issue. These are ‘Zero Config’ addresses.

The ‘Zero_conf’ addresses start with 169.254.xxx.xxx Range possible = to

This address range is what you will find on a ‘Windows’ PC that can not connect or cannot find a DHCP server.

You will see it on a Windows PC as an ‘Autoconfiguration Address’. When you see a 169.254.xxx.xxx address, you are probably not connected to a network.

Any other address range is not considered ‘Private’ and can cause complications when you try to connect outside of the LAN. (like to the Internet.)

This is because almost all other IP Addresses can be used publicly as Internet Addresses. Since your router is performing NAT, your computer can ‘see’ that expanded range of addresses.

This presents the issue of IP Address conflicts. (Remember that all devices must have a unique IP address.)
If your LAN IP Address range is not within the boundaries of the private ranges shown above, there is a good chance that an Internet site may have the same address as one of the devices on your LAN. You will try to access a device on your LAN and end up connecting to a porn site in Brazil or something crazy.

So just be sure when you set up a LAN, you stay within those Private Address guidelines.

For more assistance with you network range when setting up your security camera equipment, feel free to give our tech support department a call at 866-573-8878 option 3 or check out our Networking Forum on our website.


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