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     ng_netflow — Cisco's NetFlow implementation


     #include <sys/types.h>
     #include <netinet/in.h>
     #include <netgraph/netflow/ng_netflow.h>


     The ng_netflow node implements Cisco's NetFlow export protocol on a router running FreeBSD.
     The ng_netflow node listens for incoming traffic and identifies unique flows in it.  Flows
     are distinguished by endpoint IP addresses, TCP/UDP port numbers, ToS and input interface.
     Expired flows are exported out of the node in NetFlow version 5/9 UDP datagrams.  Expiration
     reason can be one of the following:

     -   RST or FIN TCP segment.

     -   Active timeout.  Flows cannot live more than the specified period of time.  The default
         is 1800 seconds (30 minutes).

     -   Inactive timeout.  A flow was inactive for the specified period of time.  The default is
         15 seconds.

     Node supports IPv6 accounting (NetFlow v9 only) and is aware of multiple fibs.  Different
     fibs are mapped to different domain_id in NetFlow V9 and different engine_id in NetFlow V5.


     This node type supports up to NG_NETFLOW_MAXIFACES (default 65536) hooks named iface0,
     iface1, etc., and the same number of hooks named out0, out1, etc., plus two export hooks:
     export (for NetFlow version 5) and export9 (for NetFlow version 9).  Export can be done
     simultaneously for all supported export hooks.  By default (ingress NetFlow enabled) node
     does NetFlow accounting of data received on iface* hooks.  If corresponding out hook is
     connected, unmodified data is bypassed to it, otherwise data is freed.  If data is received
     on out hook, it is bypassed to corresponding iface hook without any processing (egress
     NetFlow disabled by default).  When full export datagram for an export protocol is built it
     is sent to the export or export9 hook.  In normal operation, one (or more) export hook is
     connected to the inet/dgram/udp hook of the ng_ksocket(4) node.


     This node type supports the generic control messages, plus the following:

     NGM_NETFLOW_INFO (info)
          Returns some node statistics and the current timeout values in a struct

     NGM_NETFLOW_IFINFO (ifinfo)
          Returns information about the ifaceN hook.  The hook number is passed as an argument.

     NGM_NETFLOW_SETDLT (setdlt)
          Sets data link type on the ifaceN hook.  Currently, supported types are DLT_RAW (raw IP
          datagrams) and DLT_EN10MB (Ethernet).  DLT_ definitions can be found in <net/bpf.h>
          header.  Currently used values are 1 for DLT_EN10MB and 12 for DLT_RAW.  This message
          type uses struct ng_netflow_setdlt as an argument:

              struct ng_netflow_setdlt {
                      uint16_t iface;         /* which iface dlt change */
                      uint8_t  dlt;           /* DLT_XXX from bpf.h */

          The requested ifaceN hook must already be connected, otherwise message send operation
          will return an error.

     NGM_NETFLOW_SETIFINDEX (setifindex)
          In some cases, ng_netflow may be unable to determine the input interface index of a
          packet.  This can happen if traffic enters the ng_netflow node before it comes to the
          system interface's input queue.  An example of such a setup is capturing a traffic
          between synchronous data line and ng_iface(4).  In this case, the input index should be
          associated with a given hook.  The interface's index can be determined via
          if_nametoindex(3) from userland.  This message requires struct ng_netflow_setifindex as
          an argument:

              struct ng_netflow_setifindex {
                      uint16_t iface;         /* which iface index change */
                      uint16_t index;         /* new index */

          The requested ifaceN hook must already be connected, otherwise the message send
          operation will return an error.

     NGM_NETFLOW_SETTIMEOUTS (settimeouts)
          Sets values in seconds for NetFlow active/inactive timeouts.  This message requires
          struct ng_netflow_settimeouts as an argument:

              struct ng_netflow_settimeouts {
                      uint32_t inactive_timeout;      /* flow inactive timeout */
                      uint32_t active_timeout;        /* flow active timeout */

     NGM_NETFLOW_SETCONFIG (setconfig)
          Sets configuration for the specified interface.  This message requires struct
          ng_netflow_setconfig as an argument:

              struct ng_netflow_setconfig {
                      uint16_t iface;         /* which iface config change */
                      uint32_t conf;          /* new config */
              #define NG_NETFLOW_CONF_INGRESS         1
              #define NG_NETFLOW_CONF_EGRESS          2
              #define NG_NETFLOW_CONF_ONCE            4
              #define NG_NETFLOW_CONF_THISONCE        8
              #define NG_NETFLOW_CONF_NOSRCLOOKUP     16
              #define NG_NETFLOW_CONF_NODSTLOOKUP     32

          Configuration is a bitmask of several options.  Option NG_NETFLOW_CONF_INGRESS enabled
          by default enables ingress NetFlow generation (for data coming from ifaceX hook).
          Option NG_NETFLOW_CONF_EGRESS enables egress NetFlow (for data coming from outX hook).
          Option NG_NETFLOW_CONF_ONCE defines that packet should be accounted only once if it
          several times passes via netflow node.  Option NG_NETFLOW_CONF_THISONCE defines that
          packet should be accounted only once if it several times passes via exactly this
          netflow node.  These two options are important to avoid duplicate accounting when both
          ingress and egress NetFlow are enabled.  Option NG_NETFLOW_CONF_NOSRCLOOKUP skips radix
          lookup on flow source address used to fill in network mask.  Option
          NG_NETFLOW_CONF_NODSTLOOKUP skips radix lookup on destination (which fills egress
          interface id, destination mask and gateway).  If one doesn't need data provided by
          lookups, he/she can disable them, to reduce load on routers.

     NGM_NETFLOW_SETTEMPLATE (settemplate)
          Sets various timeouts to announce data flow templates (NetFlow v9-specific). This
          message requires struct ng_netflow_settemplate as an argument:

              struct ng_netflow_settemplate {
                      uint16_t time;          /* max time between announce */
                      uint16_t packets;       /* max packets between announce */

          Value of time field represents time in seconds to re-announce data templates.  Value of
          packets field represents maximum packets count between re-announcing data templates.

     NGM_NETFLOW_SETMTU (setmtu)
          Sets export interface MTU to build packets of specified size (NetFlow v9-specific).
          This message requires struct ng_netflow_setmtu as an argument:

              struct ng_netflow_setemtu {
                      uint16_t mtu;           /* MTU for packet */

          Default is 1500 bytes.

          This control message asks a node to dump the entire contents of the flow cache.  It is
          called from flowctl(8), not directly from ngctl(8).

     NGM_NETFLOW_V9INFO (v9info)
          Returns some NetFlow v9 related values in a

              struct ng_netflow_v9info {
                  uint16_t        templ_packets;  /* v9 template packets */
                  uint16_t        templ_time;     /* v9 template time */
                  uint16_t        mtu;            /* v9 MTU */


     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or when all hooks have
     been disconnected.


     The simplest possible configuration is one Ethernet interface, where flow collecting is

           /usr/sbin/ngctl -f- <<-SEQ
                   mkpeer fxp0: netflow lower iface0
                   name fxp0:lower netflow
                   connect fxp0: netflow: upper out0
                   mkpeer netflow: ksocket export inet/dgram/udp
                   msg netflow:export connect inet/

     This is a more complicated example of a router with 2 NetFlow-enabled interfaces fxp0 and
     ng0.  Note that the ng0: node in this example is connected to ng_tee(4).  The latter sends
     us a copy of IP packets, which we analyze and free.  On fxp0: we do not use tee, but send
     packets back to either node.

           /usr/sbin/ngctl -f- <<-SEQ
                   # connect ng0's tee to iface0 hook
                   mkpeer ng0:inet netflow right2left iface0
                   name ng0:inet.right2left netflow
                   # set DLT to raw mode
                   msg netflow: setdlt { iface=0 dlt=12 }
                   # set interface index (5 in this example)
                   msg netflow: setifindex { iface=0 index=5 }

                   # Connect fxp0: to iface1 and out1 hook
                   connect fxp0: netflow: lower iface1
                   connect fxp0: netflow: upper out1

                   # Create ksocket node on export hook, and configure it
                   # to send exports to proper destination
                   mkpeer netflow: ksocket export inet/dgram/udp
                   msg netflow:export connect inet/


     setfib(2), netgraph(4), ng_ether(4), ng_iface(4), ng_ksocket(4), ng_tee(4), flowctl(8),

     B. Claise, Ed, Cisco Systems NetFlow Services Export Version 9, RFC 3954.


     The ng_netflow node type was written by Gleb Smirnoff <>, Alexander Motin
     <>, Alexander Chernikov <>.  The initial code was based on
     ng_ipacct written by Roman V. Palagin <>.


     Cache snapshot obtained via NGM_NETFLOW_SHOW command may lack some percentage of entries
     under severe load.

     The ng_netflow node type does not fill in AS numbers.  This is due to the lack of necessary
     information in the kernel routing table.  However, this information can be injected into the
     kernel from a routing daemon such as GNU Zebra.  This functionality may become available in
     future releases.