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 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 |