# man > tc-csum(8)

_Checksum_ _action_ _in_ [_tc_(8)](https://www.chedong.com/phpMan.php/man/tc/8/markdown)                        Linux                       _Checksum_ _action_ _in_ [_tc_(8)](https://www.chedong.com/phpMan.php/man/tc/8/markdown)

## NAME
       csum - checksum update action

## SYNOPSIS
       **tc **... **action csum _**UPDATE_

       _UPDATE_ := _TARGET_ [ _UPDATE_ ]

       _TARGET_ := { **ip4h **| **icmp **| **igmp **| **tcp **| **udp **| **udplite **| **sctp **| _SWEETS_ }

       _SWEETS_ := { **and **| **or **| **+ **}

## DESCRIPTION
       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
       _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
       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  recalcu‐
       lated:

              # 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
       [**tc**(8)](https://www.chedong.com/phpMan.php/man/tc/8/markdown), [**tc-pedit**(8)](https://www.chedong.com/phpMan.php/man/tc-pedit/8/markdown)

iproute2                                     11 Jan 2015                    _Checksum_ _action_ _in_ [_tc_(8)](https://www.chedong.com/phpMan.php/man/tc/8/markdown)