Manual: tc-nat

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 ef‐
       ficient 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  sepa‐
       rated  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) ad‐
       dress 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 check‐
       sum  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)