Port Address Translation: The Secret to Saving Ipv4 Addresses
Port Address Translation
Port address translation or PAT is a translation mechanism that translates multiple private IP addresses to a single shareable public IP address. An organization needs to conserve its public IP addresses. We can also use it for security purposes just like to protect an internal network from external threats. Today we use public IPV4 addresses just because of PAT. PAT is also known as NAT overload.
Key Features of PAT:
- PAT enabled us to translate multiple private IP addresses via a single public IP address.
- It differentiates different internal devices via port numbers.
- Normally, it helps in large-scale networks with a limited number of public IP addresses.
- It adds an extra layer of security by hiding internal IP addresses.
NAT Challenges
Port Exhaustion: Port Exhaustion may occur if more sessions are established than allowed.
NAT Traversal: Sometimes specific applications may face difficulties when communicating through NAT. So, it will require additional configuration or protocols.
How Does Port Address Translation Works?
The working principle of NAT Overload revolves around the modification of both IP addresses and port numbers, which is why it’s often referred to as PAT (Port Address Translation). Here’s a simplified breakdown of how it works:
- Device Communication with External Network:
When a local or internal PC in our network wants to go on the internet, it sends a packet with its private IP address and port number to the NAt router.
- Translation by the NAT Router:
NAT or PAT works at an edge router and this router creates a database that maps private IP addresses and port numbers to a public IP address and port number. Also, the router replaces the Source port number to a unique port number on the public side.
- Communication with the External Network:
The router forwards the packet with the translated public IP address and port number over the internet. When it reaches to the destination server, then it responds to the request and sends the packet back to the router using the translated public IP address and port number.
- Reverse Translation
When the destination sends the response back to the NAT router. The public IP address and port number are then mapped back to the original internal private IP address and port number using its translation table. So, the NAT router forwards the desired packet to the correct internal device or PC, which ultimately completes the communication cycle.
PAT Lab Topology
We will use the following lab topology, which has the same infrastructure that we have used for static and Dynamic NAT. Our main objective is to translate R1’s LAN private IP address into a single shareable public IP address.
- Configure all the IP addresses as written in the diagram.
- Configure a default route on both the routers, R1 and R2
- Check the routing tables of all the routers
- Ping from PC1 to HTTP server to ensure connectivity
Configuring PAT OR NAT overload on R1
The following steps are used to configure NAT overload or PAT. It will translate all the internal private network PCs into a single shareable public IP. The PAT will use R1 fast ethernet 0/0 outside the configured IP (1.1.1.1/30).
In the next step, define internal and external interfaces for translation.
check the translation table at R1.
There is no translation table because we didn’t generate any traffic or there is no traffic flowing through the router currently right now!
Generate some traffic by pinging and browsing from PC1 to the HTTP server. Also, ping from the HTTP server to PC1, and after that, check the translation table.
The Traffic is coming and outgoing through only one shareable IP address, which is 1.1.1.1. Also, when it the traffic is going on the internet, then the port number is also attached to its packets.
