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

# [NAME](#NAME)

csum - checksum update action

# [SYNOPSIS](#SYNOPSIS)

**tc** ... **action csum** *UPDATE*

*UPDATE* := *TARGET* \[ *UPDATE* ]

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

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

# [DESCRIPTION](#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](#OPTIONS)

[*TARGET*](#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**](#SWEETS)

These are merely syntactic sugar and ignored internally.

# [EXAMPLES](#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 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](#SEE_ALSO)

[**tc**(8)](/man/os/iproute2/tc.8), [**tc-pedit**(8)](/man/os/iproute2/tc-pedit.8)

11 Jan 2015 iproute2

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Document: tc-csum(8) from iproute2 7.2.0-r0 (Chainguard OS)
Source: https://kernel.googlesource.com/pub/scm/network/iproute2/iproute2