man > tc-nat(8)

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 desir‐
       able 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 state‐
       less 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 embed‐
       ded 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)