Private vs Public IP Checker

You just set up a home server and now no one can connect to it from the Internet. Why? Because private vs. Public IP addresses is different things (yet most of us treat them as the same). When something goes wrong, we’re lost because we don’t know why our port forward doesn’t work. Knowing what’s what gets you troubleshooting without guesswork.

So, the calculator tell you what type of address you’ve got and thus points you to a potential solution. That’s important because not all private addresses is equal. Some are standard local network addresses, which are designed to be private. Others are carrier-grade NAT addresses, meaning your ISP are sharing one single public IP among lots of user.

Fix Your Home Server Connection Problems

How do you account for that when planning remote access? Traditional port forwarding won’t cut it if your router has shared NAT, regardless of whether or not you configure your router correct. ISPs are using Carrier-Grade NAT because they is running out of v4 addresses.

What does this mean? If you look at the WAN page of your router you may see something like a public IP address assigned to you, which it isn’t. Why not? There’s no route from the outside world to that range. The tool will tell you by scanning certain RFC ranges. It’ll also flag any link-local addresses. Typically this means your DHCP server didn’t gave you a lease. It is an internal plumbing thing, not a routing problem in the internet itself.

The repair steps are intended to be a starting point. The checkers might recommend a VPN or tunnel because they know those will punch right through a blocked inbound connection. A reverse tunnel instead establish an outbound connection from your server to a publicly available relay. Traffic flows back through NAT barrier via this outbound pipe, which doesn’t open any holes in your firewall.

That’s typically more convenient than opening ports directly on your home router. Opening ports leaves you exposed to constant port scans by botnets seeking vulnerable services. Safety and convenience is at odds here. A tunnel meets both requirements.

The way we see firewalls also change with IPv6. Although there is huge address space, there is no more NAT to protect us from. With IPv6, every host get a global unicast address, which means: Public. It can be reached from anywhere. People who grew up using IPv4 tend to believe that NAT continues to protect their devices. It doesn’t. If you have an IPv6 host, all your protection are in firewall rules that block unwanted traffic. Your public IP needs active protection, not passive isolation.

For instance, you might not know that a change to your firewall settings can’t correct problems with DHCP. You might also think that the example ranges given in a tutorial will be active in your own network. (They won’t, those are reserved for demonstration purposes and do not pass traffic through the public internet.) Always check what range was actualy assigned to you using an outside checker.

The included reference tables describes the differences and how they’ll affect your efforts. Saving you the wasted time of working on addresses that aren’t capable of passing anything between network. Knowing what direction your traffic travels is part of getting your home server online. Knowing if your home has private, public, or shared addresses lets you select an appropriate way to proceed. It stops you from guessing what’s wrong with your connection and helps you configure your systems to work with your network reality. It makes a frustrating problem become something that you can manage.

You should of checked the settings first.