# phpman > 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)