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+PNAT 1:1 match & rewrite NAT
+============================
+
+PNAT is a stateless statically configured, match and rewrite plugin. It
+uses a set of match and rewrite rules that are applied on the IP input
+and output feature paths. A PNAT rule is unidirectional.
+
+The match is done using up to a 6-tuple; IP source and destination
+address, IP protocol, transport layer source and destination ports, and
+FIB table / interface index.
+
+While multiple match/rewrite rules can be applied to an interface (per
+direction), the match pattern must be the same across all rules on that
+interface/direction.
+
+If required in the future, matching could be done using the general
+classifier, allowing matching on any protocol field, as well having an
+ordered set of match patterns.
+
+If the packet does not match, it will by default be passed to the next
+graph node in the feature chain. If desired a different miss behaviour
+could be implemented, e.g. similarly to dynamic NAT, the packet punted
+to a slow path.
+
+Rewrite instructions
+--------------------
+
+.. code:: c
+
+   typedef enum {
+     PNAT_INSTR_NONE                   = 1 << 0,
+     PNAT_INSTR_SOURCE_ADDRESS         = 1 << 1,
+     PNAT_INSTR_SOURCE_PORT            = 1 << 2,
+     PNAT_INSTR_DESTINATION_ADDRESS    = 1 << 3,
+     PNAT_INSTR_DESTINATION_PORT       = 1 << 4,
+   } pnat_instructions_t;
+
+These are the supported rewrite instructions. The IP checksum and the
+TCP/UDP checksum are incrementally updated as required.
+
+There are only a few “sanity checks” on the rewrites. For example, the
+rewrite in the outbound direction is applied on the ip-output feature
+chain. If one were to rewrite the IP destination address, the routing
+decision and determination of the next-hop has already been done, and
+the packet would still be forwarded to the original next-hop.