IPヘッダ
The simplest type of NAT provides a one-to-one translation of IP addresses. RFC 2663 refers to this type of NAT as "basic NAT"; it is also called a "one-to-one NAT". In this type of NAT, only the IP addresses, IP header checksum, and any higher-level checksums that include the IP address are changed. Basic NAT can be used to interconnect two IP networks that have incompatible addressing.