NAT action in tc(8)		     Linux		   NAT action in tc(8)



NAME
       nat - stateless native address translation action

SYNOPSIS
       tc ... action nat DIRECTION OLD NEW

       DIRECTION := {  ingress | egress }

       OLD := IPV4_ADDR_SPEC

       NEW := IPV4_ADDR_SPEC

       IPV4_ADDR_SPEC := {  default | any | all |  in_addr[/{prefix|netmask}]

DESCRIPTION
       The nat action allows one to perform NAT without the overhead of
       conntrack, which is desirable if the number of flows or addresses to
       perform NAT on is large. This action is best used in combination with
       the u32 filter to allow for efficient lookups of a large number of
       stateless NAT rules in constant time.

OPTIONS
       ingress
	      Translate destination addresses, i.e. perform DNAT.

       egress Translate source addresses, i.e. perform SNAT.

       OLD    Specifies addresses which should be translated.

       NEW    Specifies addresses which OLD should be translated into.

NOTES
       The accepted address format in OLD and NEW is quite flexible. It may
       either consist of one of the keywords default, any or all, representing
       the all-zero IP address or a combination of IP address and netmask or
       prefix length separated by a slash (/) sign. In any case, the mask (or
       prefix length) value of OLD is used for NEW as well so that a one-to-
       one mapping of addresses is assured.

       Address translation is done using a combination of binary operations.
       First, the original (source or destination) address is matched against
       the value of OLD.  If the original address fits, the new address is
       created by taking the leading bits from NEW (defined by the netmask of
       OLD) and taking the remaining bits from the original address.

       There is rudimental support for upper layer protocols, namely TCP, UDP
       and ICMP.  While for the first two only checksum recalculation is
       performed, the action also takes care of embedded IP headers in ICMP
       packets by translating the respective address therein, too.

SEE ALSO
       tc(8)

iproute2			  12 Jan 2015		   NAT action in tc(8)