NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       nat - stateless native address translation action

SYNOPSIS         top

       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         top

       The nat action allows 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         top

       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         top

       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         top

       tc(8)

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was obtained
       from the project's upstream Git repository 
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git⟩
       on 2017-05-03.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-to-
       date source for the page, or you have corrections or improvements to
       the information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

iproute2                         12 Jan 2015             NAT action in tc(8)