Inside Local, Inside Global, Outside Local, Outside Global

Cisco classifies the IPv4 addresses used for Network Address Translation (NAT) as four types. This four types of addresses present in other Network Address Translation (NAT) implementation also. Inside Local address – Consider the term "Inside" as inside our network. Inside local address is an IP address assigned to a workstation inside our network. Inside Local addresses are typically private IP addresses, which stay inside our network. Inside Global address - Inside Global address are typically public IP addresses which are assigned to our end internet facing router to be used as the IP address for communicating with other devices in the internet. The Inside Local IP addresses are removed at the NAT router and translated with Inside Global address. An IP datagram moves out to the internet from our private network will always has an IP address from Inside Global address range as the source IP address. Outside Global address - Outside Global address is the public IP address assigned to the end device on the other network to communicate other devices in the internet. Outside Global addresses are public IP addresses which are routable. Outside local address - Outside local address is the real IP address of the end device at other network. Outside local addresses are typically private IP addresses assigned to the computers in the other private network. We cannot know the Outside local addresses because in a NAT enabled network we use the destination IP address as Outside Global address.