Private Addresses and NAT: The Trick at the Gate
8:14Coming soon
The same address, 192.168.1.10, is on a computer in your house, in mine, and in millions of others, and nothing breaks. This lesson explains why: three private ranges anyone can use because they are never routed on the internet, and the trick your router plays at the gate so all those private hosts can still reach the web through one public address. The mail bag's address tag, untouched since the Layer 3 lesson, finally gets rewritten.
You'll learn
- The three private ranges (10/8, 172.16/12, 192.168/16) and why they can repeat in every network on Earth
- Why private addresses are never routed on the internet, and what that means at the router
- NAT: the router rewrites the source address on the way out and the destination on the way back, with a translation table
- PAT (NAT overload): how the source port lets one public IP serve a whole network
- Why nobody outside can start a connection in, and how port forwarding opens one door on purpose
- Two symptoms the exam loves: a public address configured inside a private network, and a 169.254 APIPA address
- The real thing: ipconfig inside, "what is my IP" outside, and the router status page with WAN, LAN, NAT and one forwarding rule
- Exam corner: the most likely cause of a 169.254.98.17 address
Chapters
- 0:00The same sign on millions of lawns
- 0:46Three free ranges
- 1:25Never routed on the internet
- 1:52The gate's second sign: NAT
- 3:02One sign, a whole street: PAT
- 3:57Nobody can ring your bell
- 4:18Port forwarding
- 4:42Two symptoms: a public sign inside, and 169.254
- 5:11The real names
- 6:18The real thing: inside, outside, the router page
- 7:04Exam corner
- 7:26Recap and next time
Exam objectives: CompTIA Network+ N10-009: 1.7 (public vs private addressing, RFC 1918, NAT and PAT, port forwarding basics, APIPA), 5.2 (incorrect IP configuration symptoms), 5.5 (ipconfig).
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