tc-csum(8) — Linux manual page

Checksum action in tc(8)          Linux          Checksum action in tc(8)

NAME         top

       csum - checksum update action

SYNOPSIS         top

       tc ... action csum UPDATE

       UPDATE := TARGET [ UPDATE ]

       TARGET := { ip4h | icmp | igmp | tcp | udp | udplite | sctp |
               SWEETS }

       SWEETS := { and | or | + }

DESCRIPTION         top

       The csum action triggers checksum recalculation of specified
       packet headers. It is commonly used to fix incorrect checksums
       after the pedit action has modified the packet content.

OPTIONS         top

       TARGET Specify which headers to update: IPv4 header (ip4h), ICMP
              header (icmp), IGMP header (igmp), TCP header (tcp), UDP
              header (udp), UDPLite header (udplite) or SCTP header
              (sctp).

       SWEETS These are merely syntactic sugar and ignored internally.

EXAMPLES         top

       The following performs stateless NAT for incoming packets from
       192.0.2.100 to new destination 198.51.100.1. Assuming these are
       UDP packets, both IP and UDP checksums have to be recalculated:

              # tc qdisc add dev eth0 ingress handle ffff:
              # tc filter add dev eth0 prio 1 protocol ip parent ffff: \
                   u32 match ip src 192.0.2.100/32 flowid :1 \
                   action pedit munge ip dst set 198.51.100.1 pipe \
                   csum ip and udp

SEE ALSO         top

       tc(8), tc-pedit(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
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2025-08-11.  (At that time, the date of the most recent commit
       that was found in the repository was 2025-08-08.)  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                       11 Jan 2015       Checksum action in tc(8)

Pages that refer to this page: tc-actions(8)

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