MIP in Juniper ScreenOS
For those familiar with JUNOS, MIP in ScreenOS is equivalent to Static NAT in JUNOS. Mapping of one IP address to another directly is called MIP. Essentially, a MIP is static destination address translation, mapping the Destination IP address in an IP packet header to another static IP address. When a host with MIP initiates outbound traffic, the security device translate source IP address of the host to MIP address. This Bidirectional translation is different from behavior of source and Destination address translation.
An example can substantiate the understanding of MIP –
If the security device applies a policy NAT – destination for traffic sent from Host 1 to Host 2, the security device translates the original destination IP address from 184.108.40.206 to 220.127.116.11 (It also translates the source IP address from 18.104.22.168 to 22.214.171.124 while the receiving host 2 responds back to host 1)
MIPs allow inbound traffic to reach private addresses in a zone whose interface is in NAT mode. MIPs also provide part of the solution to the problem of overlapping address spaces at two sites connected by a VPN tunnel.