TL;DR: Addresses that start with 192.168, 10., or 172.16–31 live inside your private network. The public IP is the one outside your router that websites see. Mixing them up breaks allowlists and support tickets. Check the public value on the homepage IP lookup before you paste anything into a vendor form.
A screenshot that looked confident and was useless
Someone rented a cabin with “work-friendly Wi‑Fi” and needed to whitelist himself on a client firewall. He photographed the guest network card on his phone: IP 192.168.4.88, subnet mask, DNS. The firewall team politely rejected it. Those numbers describe the cabin’s internal hallway. From the internet, every guest shared one public exit. Until he reported that exit, no rule could help him.
The rejection felt personal until someone explained NAT in one sentence: private addresses stop at the router; the world only sees the router’s WAN side. His screenshot was perfect for fixing a Chromecast on the guest LAN. It was the wrong artifact for a cloud firewall that never touched the cabin’s internal DHCP pool.
Private space is reusable on purpose
RFC private ranges exist so millions of homes can reuse the same LAN numbers without colliding on the public internet. Your printer at 192.168.1.50 and a stranger’s printer at 192.168.1.50 never meet. NAT at the router translates many private clients into one (or a few) public addresses. That translation is why the number on your laptop status page is usually not the number in a remote server’s access log.
- 192.168.0.0/16: home routers and small offices.
- 10.0.0.0/8: large private and cloud VPC layouts.
- 172.16.0.0/12: another private block, easy to mistake for “public-looking.”
Cloud engineers live in 10.x space all day. A 10.0.2.15 address inside a lab VM is as private as a cabin guest’s 192.168.4.88. The mistake is assuming “looks professional” means “routable on the public internet.” Only addresses outside the reserved private and special-use ranges participate in global routing the way a bank’s login page cares about.
How to tell which number you are holding
If the first octet patterns match the list above, treat it as local until proven otherwise. If a lookup page shows a different dotted quad or an IPv6 string with colons, that is the public view. IPv6 can complicate the story—some networks give you a global IPv6 while still using private IPv4 inside—but the rule of thumb stays: the address a remote HTTPS site logs is the one that matters for allowlists.
Link-local addresses like 169.254.x.x mean “no DHCP yet” on many systems. They are not public either. APIPA addresses show up when a cable is loose or a VLAN is wrong; pasting them into a vendor portal wastes the same hour as pasting 192.168.
When both appear in one traceroute
Traceroute may show private hops near you and public hops later. That is normal. Do not pick the first hop and call it “my IP” for a SaaS form. Pick the address a what-is-my-IP tool returns while you are on the same path you will use for work. If your ISP uses carrier-grade NAT, you might not even see your true public address on the router—only the lookup or the ISP portal shows the shared exit your traffic uses.
Double NAT and guest networks
Mesh kits and “guest Wi‑Fi” often create a second private layer. Your phone might be 192.168.86.40 behind a satellite node while the main router still NATs everything to one WAN IP. The public address is still singular toward the internet; the private one is still useless for a remote allowlist. When IT asks for “the IP of the user,” they mean the outermost public source, not the guest subnet.
Port forwarding instructions on forums frequently confuse LAN and WAN. “Forward port 443 to 192.168.1.100” is an internal rule. The public side is whatever the lookup shows today. If that public side changes tomorrow, the forward rule still works locally—the remote client just dials the wrong target until someone updates the bookmark.
Fix the ticket language
Write “public IP as seen by websites” when you ask teammates for a number. Write “LAN address” when you mean printer or NAS access. Ambiguous “send me your IP” is how cabins, hotels, and CGNAT mobile plans waste an afternoon. If location context is needed too, pair the address with the city estimate from the location page, and label both as network-exit data.
Teaching new hires this distinction once saves dozens of misrouted tickets. Private numbers are abundant and reusable; public numbers are scarce and often shared. The lookup page exists precisely so you do not have to decode which column on a router screenshot is which when a client firewall is blocking your login.
Security awareness training sometimes shows a scary map next to an IP address. The lesson lands better when you separate “this is my home LAN label” from “this is how the bank’s server addressed my router.” One is invisible off the property; the other is the only one that belongs in an allowlist email.
