Frequently Asked Questions of NAT & PAT
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FAQ Execution
BGP (Border Gateway Protocol) is a path-vector routing protocol used to exchange routing information between Autonomous Systems (AS).
NAT (Network Address Translation) translates private IP addresses to public IP addresses.
PAT (Port Address Translation) maps multiple private IPs to a single public IP using ports.
To conserve public IPv4 addresses and enable internet access for private networks.
Because many internal hosts share one public IP via different port numbers.
On edge routers or firewalls connecting to the internet.
IPv4 address exhaustion.
An address used inside local networks, not routable on the internet.
An address routable over the internet.
Yes, it changes source or destination IP (and ports in PAT).
Generally no, due to large address space.
One-to-one mapping between private and public IP.
Maps private IPs to a pool of public IPs.
Many-to-one mapping using ports.
Both source and destination addresses are translated.
NAT applied based on defined policies (ACLs, routes, etc.).
Changes the destination IP in incoming traffic.
Changes the source IP in outgoing traffic.
Forwarding specific ports from public IP to internal server.
A range of public IPs used for dynamic NAT.
Traffic passes without translation.
By assigning unique source port numbers.
A table maintaining mappings of private-to-public addresses and ports.
New sessions cannot be translated.
Yes, due to translation overhead.
Protocols embedding IP info (e.g., FTP, SIP).
Techniques to allow traffic through NAT devices.
The duration a mapping stays active without traffic.
Indirectly hides internal IPs but is not a firewall.
Yes.
Yes.
For hosting internal servers accessible from the internet.
When multiple public IPs are available.
When only one public IP is available.
Internal users accessing internal server via public IP.
Same as hairpin NAT.
Yes, PAT assigns different external ports.
Using inside and outside interfaces and rules.
Clients receive private IPs and are translated by NAT.
Yes, may require NAT-T (NAT Traversal).
Traffic that bypasses NAT rules.
📚 Advanced Concepts
NAT performed by ISPs to share public IPs among customers.
Each connection gets a unique mapping.
One mapping allows any external host to respond.
Only specific external hosts can reply.
Replies allowed only from specific IP and port.
By allowing reuse of private IPs.
NAT translation table and session logs.
Commands showing NAT table and statistics.
Breaks end-to-end connectivity principle.
Yes, in almost all IPv4 networks.
