What Is Dynamic NAT? Configuring Dynamic NAT
Learn how dynamic network address translation (NAT) works, how it differs from static NAT, and when to use it.
Dynamic NAT Basics
Dynamic NAT maps internal private IP addresses to a pool of public IP addresses on an as-needed basis. When an internal host initiates outbound traffic, the NAT device temporarily assigns it one of the available public addresses from the pool.
Once the connection ends or the translation timeout expires, that public address can be reused for another internal host. Unlike many-to-one PAT (Port Address Translation), dynamic NAT maintains a one-to-one mapping for each active session.
Dynamic NAT vs. Static NAT and PAT
Static NAT permanently maps a single private IP to a single public IP, which is useful for servers that must always appear at the same external address. Dynamic NAT automates mapping for outbound connections without requiring dedicated public IPs for each internal host.
Port Address Translation (PAT), often called NAT overload, maps many internal hosts to a single public IP by tracking port numbers. Dynamic NAT sits between these concepts, offering flexibility when you have a small pool of public addresses and need simultaneous unique mappings.
Configuration Considerations for Dynamic NAT
When configuring dynamic NAT on routers or firewalls, you define inside and outside interfaces, specify the internal networks to translate, and allocate a pool of public addresses. Access control lists (ACLs) or policies determine which traffic is eligible for translation.
Monitoring translation tables and log entries helps you understand how the pool is being used and whether you need more public addresses. In some environments, dynamic NAT is combined with PAT and static mappings to meet different application requirements.