IP Address

Introduction NAT (Network Address Translation) is a core technology that mediates between private IP addresses and public IP addresses in network communications. It emerged in the mid-1990s to address the IPv4 address depletion problem and was first standardized through the IETF’s RFC 1631 document. Today, NAT has become an essential technology forming the foundation of global internet infrastructure, from home routers to large-scale corporate networks and cloud infrastructure. Basic Concepts of NAT NAT operates on network devices such as routers or firewalls, translating IP addresses between internal networks (private IP) and external networks (public IP). During this process, it modifies the IP addresses and TCP/UDP port numbers in packet headers and records the translation information in a NAT table to enable bidirectional communication. Private IP address ranges defined in RFC 1918 (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are widely used in internal network configurations in NAT environments. When a packet passes through a NAT device, the checksum is also recalculated, which is essential to ensure the integrity of IP and TCP/UDP headers. ...

ARP(Address Resolution Protocol) is a protocol that finds the MAC address corresponding to an IP address. When communication occurs between devices on a network, it is necessary to find out the MAC address to deliver the packet to the destination. The Role of ARP Convert IP addresses to MAC addresses Identify devices that can communicate directly within the network Optimize performance through ARP caching Detect duplicate IP conflicts (using Gratuitous ARP) ARP Operation Process 1. ARP Request (ARP Request) When a host knows the destination IP address but not the MAC address, it broadcasts an ARP request to the network. ...