Static NAT vs Dynamic NAT

Static NAT: A Fixed One-to-One Mapping

Static NAT permanently maps one specific private IP address to one specific public IP address, and that mapping never changes.

192.168.1.10  <----- always maps to ----->  203.0.113.10  (fixed, permanent)

This is typically used for servers that need to be consistently reachable from the outside world at the same address every time - like a company's public web server.

Dynamic NAT: A Shared Pool of Addresses

Dynamic NAT maps private addresses to public addresses drawn from a pool, assigned temporarily on an as-needed basis rather than a fixed permanent mapping.

Available public pool: 203.0.113.1, 203.0.113.2, 203.0.113.3

Device A connects -> temporarily assigned 203.0.113.1
Device B connects -> temporarily assigned 203.0.113.2
Device A disconnects -> 203.0.113.1 returns to the available pool

This still requires roughly one public address per simultaneously active device, so it saves some addresses compared to giving every device a permanently dedicated one, but not nearly as much as PAT (covered in the next note).

Comparing the Two

Why Home Routers Use Neither of These

Most home and small office routers actually use PAT instead of plain dynamic NAT, since PAT lets an entire network share a single public address at once - covered in detail in the next note in this section.