NAT (Network Address Translation)

What is a private network?

A network that uses private IP addresses not routable on the public internet

Can private IP addresses be used on the global internet?

No, they are not routable on the public internet

Why can’t packets with private IP addresses reach the internet?

Public networks do not recognize private address ranges

Can devices on the internet initiate communication with private IP addresses?

No, private addresses are not reachable from the public internet

What is Network Address Translation (NAT)?

A method of translating private IP addresses into public IP addresses for internet communication

Where is NAT typically implemented?

On a router at the boundary between private and public networks

What is the basic purpose of NAT?

Allow private network devices to communicate with the public internet

What does NAT do to packet addresses?

Replaces private source IP with a public IP address

What is Static NAT?

A one-to-one mapping between a private IP and a public IP

Why would you use Static NAT?

For security, filtering, or hosting services like web servers

What is Dynamic NAT?

A mapping of private IPs to a pool of public IP addresses

How does Dynamic NAT work?

Assigns an available public IP from a pool to a private device temporarily

What is NAT Overloading (PAT)?

Mapping multiple private IPs to a single public IP using port numbers

What does PAT stand for?

Port Address Translation

Where is NAT overloading commonly used?

Home and small office networks

What is Overlapping NAT?

A NAT method used when networks with identical IP ranges must communicate

When is overlapping NAT used?

During mergers or when duplicate IP ranges exist

What is IP pooling in NAT?

Using a pool of public IP addresses for dynamic assignment

What happens when a device connects using pooled NAT?

It is assigned an available public IP from the pool

What is IP masquerading?

Another term for NAT overloading (PAT)

What information in a packet helps NAT track connections?

Source IP, source port, destination IP, destination port

Why are port numbers important in NAT overloading?

They create unique identifiers for each connection

What does NAT do to the source IP in outgoing packets?

Replaces it with a public IP address

How does NAT handle returning packets?

Uses a translation table to map back to the original private IP

What happens if two devices use the same source port?

NAT assigns different external ports to avoid conflicts

What is TCP/IP multiplexing?

Using multiple port numbers to maintain multiple simultaneous connections

What is the order of operations (inside to outside)?

Inbound ACL → routing → NAT → outbound ACL

What is the order of operations (outside to inside)?

Inbound ACL → NAT → routing → outbound ACL

Why are NAT and routing steps reversed depending on direction?

Because address translation must occur before or after routing depending on traffic flow

What are some concerns about NAT?

Breaks end-to-end connectivity, complicates protocols, and adds processing overhead

What command shows NAT statistics?

show ip nat statistics

What command shows NAT translation entries?

show ip nat translations

How do you clear NAT translations?

clear ip nat translation *

What command is used to debug NAT?

debug ip nat