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

SEE ALSO

       tc(8), tc-pedit(8)