Day 3: How to Determine Public vs. Private IP Addresses

This post continues our 20 Day Challenge to understand the technical aspects of videoconferencing.

Why Do IP Addresses Matter?

IP Addresses are used in standards-based H.323 videoconferencing; not for Skype or other proprietary desktop / web based conferencing tools.

Many corporations only videoconference within their network and therefore don’t need to dial IP addresses. But in the K12 space, we are always dialing out to schools outside of our network / area. So, the way to dial other people is to use their IP address. (Usually. More on other H.323 dialing in a later posts on gatekeepers and firewall traversal units.)

To be able to receive a call from someone, you need to know your public IP address!

Public IP Addresses

A public IP (Internet Protocol) address is an number that is accessible by anyone on the internet. Public IP addresses are reserved for public access. They are used to direct traffic coming in from outside your network. IP address look like this or or some similar variation. Some video conference units enter the dot with a *; and others use a dot. But the number itself has dots! The correct way to refer to it is with the term dot (not period or star or asterisk).

Private IP Addresses

Private IP addresses are used only within your network. No one outside your network can dial a private IP address because they aren’t on your network. Think of it like dialing a phone extension within the school. Outsiders couldn’t get you with just that 3 or 4 digit number. They have to dial the full public number. In this case, they can look similar; the difference is what the number starts with. Private IP addresses always start with:

  • 10.x.x.x
  • 172.16.x.x
  • 192.168.x.x

Dynamic or Static?

You also need to know if your IP is dynamic or static. Dynamic IP addresses change. They can change when a computer (or videoconference system) is rebooted, or when something changes on the network. Static IP addresses are always the same number. Many videoconference systems are installed with a static IP address, as this makes it much easier for others to dial you.

What do you know about your IP address?

  • Does it always stay the same? or does it change?
  • If it changes, do you know how often it changes? What triggers the change? When and how often do you need to check if it changed?

For example, some schools use cable to access the Internet and may not invest in static IP addresses (they usually cost extra with cable). In this case, often when the equipment is turned off and on again, it picks up a new IP address. This behavior is called “dynamic”.


Your Turn

  • Do you know your public IP address?
  • Do you know if your address is dynamic or static?

Team-written by Janine Lim, Shane Howard, and Roxanne Glaser. The opinions expressed in these posts are based on our collective video conference experience connecting classes across multiple networks to connect them to zoos, museums, experts and other classes during the past 10 years. This series of posts reflects our usage and understanding, not that of any vendor or manufacturer. No one is paying us to write these. We are just sharing what we have learned.

5 replies on “Day 3: How to Determine Public vs. Private IP Addresses”

    • You’re exactly right, Madell! We have on our list several more posts about how the aliases come in, and dialing tips for the different units etc. So stay tuned for more! šŸ™‚

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