Understanding PAT (NAT Overload) for CCNA
PAT (NAT Overload) maps multiple private IP addresses to a single public IP address by utilizing unique source port numbers to track sessions.
The Power of PAT
Port Address Translation (PAT), also known as NAT Overload, allows thousands of internal devices to share a single public IP address, drastically conserving IPv4 space.
How PAT Tracks Sessions
When a packet leaves the router, PAT modifies the source IP to the public IP and assigns a unique source port number. It uses this port number to route returning traffic back to the correct internal host.
Configuring PAT
Configure PAT using an interface: `ip nat inside source list [acl] interface [type/num] overload`. The `overload` keyword is what enables PAT.
❓ Frequently Asked Questions
How many devices can share one public IP with PAT?
Theoretically up to 65,536 (the number of available ports), but practically a few thousand due to resource limits.
What is the crucial keyword for PAT configuration?
The keyword `overload` is required to enable Port Address Translation.
Can PAT use a pool instead of an interface?
Yes, you can use `ip nat inside source list [acl] pool [name] overload`.