Destination NAT (DNAT) in SR OS is supported for LSN44 and L2-Aware NAT. DNAT can be used for traffic steering where the destination IP address of the packet is rewritten. In this fashion traffic can be redirected to an appliance or set of servers that are in control of the operator, without the need for a separate transport service (for example, PBR plus LSP). Applications utilizing traffic steering via DNAT normally require some form of inline traffic processing, such as inline content filtering (parental control, antivirus/spam, firewalling), video caching, and so on.
After the destination IP address of the packet is translated, traffic is naturally routed based on the destination IP address lookup. DNAT translates the destination IP address in the packet while leaving the original destination port untranslated.
Similar to source based NAT (Source Network Address and Port Translation (SNAPT)), the SR OS maintains state of DNAT translations so that the source IP address in the return (downstream) packet is translated back to the original address.
Traffic selection for DNAT processing in MS-ISA is performed via a NAT classifier.