tc-ctinfo

ctinfo action in tc(8)               Linux              ctinfo action in tc(8)

NAME
       ctinfo - tc connmark processing action

SYNOPSIS
       tc ... action ctinfo [ dscp MASK [STATEMASK] ] [ cpmark [MASK] ] [ zone
       ZONE ] [ CONTROL ] [ index <INDEX> ]

DESCRIPTION
       CTINFO (Conntrack Information) is a tc action for retrieving data  from
       conntrack marks into various fields.  At present it has two independent
       processing modes which may be viewed as sub-functions.

       DSCP mode copies a DSCP stored in conntrack's connmark into the IPv4/v6
       diffserv  field.   The  copying may conditionally occur based on a flag
       also stored in the connmark.  DSCP  mode  was  designed  to  assist  in
       restoring  packet classifications on ingress, classifications which may
       then be used by qdiscs such as CAKE.  It may be  used  in  any  circum-
       stance where ingress classification needs to be maintained across links
       that otherwise bleach or remap according to their own policies.

       CPMARK (copymark) mode copies the conntrack connmark into the  packet's
       mark  field.   Without  additional  parameters  it is functionally com-
       pletely equivalent to the existing connmark action.  An  optional  mask
       may be specified to mask which bits of the connmark are restored.  This
       may be useful when DSCP and CPMARK modes are combined.

       Simple statistics (tc -s) on DSCP restores and CPMARK copies are  main-
       tained  where  values  for  set indicate a count of packets altered for
       that mode.  DSCP includes an error count where the destination packet's
       diffserv field was unwriteable.

PARAMETERS
   DSCP mode parameters:
       mask   A  mask  of 6 contiguous bits indicating where the DSCP value is
              located in the 32 bit conntrack mark field.  A mask must be pro-
              vided for this mode.  mask is a 32 bit unsigned value.

       statemask
              A  mask of at least 1 bit indicating where a conditional restore
              flag is located  in  the  32  bit  conntrack  mark  field.   The
              statemask  bit/s  must NOT overlap the mask bits.  The DSCP will
              be restored if the  conntrack  mark  logically  ANDed  with  the
              statemask  yields  a  non-zero result.  statemask is an optional
              unsigned 32 bit value.

   CPMARK mode parameters:
       mask   Store the logically ANDed result of conntrack mark and mask into
              the  packet's  mark field.  Default is 0xffffffff i.e. the whole
              mark field.  mask is an optional unsigned 32 bit value

   Overall action parameters:
       zone   Specify the conntrack zone  when  doing  conntrack  lookups  for
              packets.  zone is a 16bit unsigned decimal value.  Default is 0.

       CONTROL
              The  following  keywords allow to control how the tree of qdisc,
              classes, filters and actions is further traversed after this ac-
              tion.

              reclassify
                     Restart with the first filter in the current list.

              pipe   Continue  with  the next action attached to the same fil-
                     ter.

              drop   Drop the packet.

              shot   synonym for drop

              continue
                     Continue classification with the next filter in line.

              pass   Finish classification process and return to calling qdisc
                     for further packet processing. This is the default.

       index  Specify an index for this action in order to being able to iden-
              tify it in later commands. index is  a  32bit  unsigned  decimal
              value.

EXAMPLES
       Example showing conditional restoration of DSCP on ingress via an IFB

              #Set up the IFB interface
              tc qdisc add dev ifb4eth0 handle ffff: ingress

              #Put CAKE qdisc on it
              tc qdisc add dev ifb4eth0 root cake bandwidth 40mbit

              #Set interface UP
              ip link set dev ifb4eth0 up

              #Add 2 actions, ctinfo to restore dscp & mirred to redirect the packets to IFB
              tc filter add dev eth0 parent ffff: protocol all prio 10 u32 \
                  match u32 0 0 flowid 1:1 action    \
                  ctinfo dscp 0xfc000000 0x01000000  \
                  mirred egress redirect dev ifb4eth0

              tc -s qdisc show dev eth0 ingress

               filter parent ffff: protocol all pref 10 u32 chain 0
               filter parent ffff: protocol all pref 10 u32 chain 0 fh 800: ht divisor 1
               filter parent ffff: protocol all pref 10 u32 chain 0 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1 not_in_hw
                match 00000000/00000000 at 0
                  action order 1: ctinfo zone 0 pipe
                  index 2 ref 1 bind 1 dscp 0xfc000000 0x01000000 installed 72 sec used 0 sec DSCP set 1333 error 0 CPMARK set 0
                  Action statistics:
                  Sent 658484 bytes 1833 pkt (dropped 0, overlimits 0 requeues 0)
                  backlog 0b 0p requeues 0

                  action order 2: mirred (Egress Redirect to device ifb4eth0) stolen
                  index 1 ref 1 bind 1 installed 72 sec used 0 sec
                  Action statistics:
                  Sent 658484 bytes 1833 pkt (dropped 0, overlimits 0 requeues 0)
                  backlog 0b 0p requeues 0

       Example showing conditional restoration of DSCP on egress

       This may appear nonsensical since iptables marking of egress packets is
       easy to achieve, however the iptables flow classification rules may  be
       extensive  and  so some sort of set once and forget may be useful espe-
       cially on cpu constrained devices.

              # Send unmarked connections to a marking chain which needs to store a DSCP
              and set statemask bit in the connmark
              iptables -t mangle -A POSTROUTING -o eth0 -m connmark \
                  --mark 0x00000000/0x01000000 -g CLASS_MARKING_CHAIN

              # Apply marked DSCP to the packets
              tc filter add dev eth0 protocol all prio 10 u32 \
                  match u32 0 0 flowid 1:1 action \
                  ctinfo dscp 0xfc000000 0x01000000

              tc -s filter show dev eth0
               filter parent 800e: protocol all pref 10 u32 chain 0
               filter parent 800e: protocol all pref 10 u32 chain 0 fh 800: ht divisor 1
               filter parent 800e: protocol all pref 10 u32 chain 0 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1 not_in_hw
                match 00000000/00000000 at 0
                  action order 1: ctinfo zone 0 pipe
                  index 1 ref 1 bind 1 dscp 0xfc000000 0x01000000 installed 7414 sec used 0 sec DSCP set 53404 error 0 CPMARK set 0
                  Action statistics:
                  Sent 32890260 bytes 120441 pkt (dropped 0, overlimits 0 requeues 0)
                  backlog 0b 0p requeues 0

SEE ALSO
       tc(8), tc-cake(8) tc-connmark(8) tc-mirred(8)

AUTHORS
       ctinfo was written by Kevin Darbyshire-Bryant.

iproute2                          4 Jun 2019            ctinfo action in tc(8)