rtnetlink - Linux IPv4 routing socket


   #include <asm/types.h>
   #include <linux/if_link.h>
   #include <linux/netlink.h>
   #include <linux/rtnetlink.h>
   #include <sys/socket.h>

   rtnetlink_socket = socket(AF_NETLINK, int socket_type, NETLINK_ROUTE);


   Rtnetlink  allows  the  kernel's routing tables to be read and altered.
   It is used within the kernel to communicate between various subsystems,
   though  this  usage  is not documented here, and for communication with
   user-space programs.  Network routes, IP  addresses,  link  parameters,
   neighbor  setups,  queueing  disciplines,  traffic  classes  and packet
   classifiers may all be controlled through NETLINK_ROUTE sockets.  It is
   based on netlink messages; see netlink(7) for more information.

   Routing attributes
   Some  rtnetlink  messages  have  optional  attributes after the initial

       struct rtattr {
           unsigned short rta_len;    /* Length of option */
           unsigned short rta_type;   /* Type of option */
           /* Data follows */

   These attributes should be manipulated using only the RTA_*  macros  or
   libnetlink, see rtnetlink(3).

   Rtnetlink  consists  of  these  message  types (in addition to standard
   netlink messages):

          Create, remove or  get  information  about  a  specific  network
          interface.    These  messages  contain  an  ifinfomsg  structure
          followed by a series of rtattr structures.

          struct ifinfomsg {
              unsigned char  ifi_family; /* AF_UNSPEC */
              unsigned short ifi_type;   /* Device type */
              int            ifi_index;  /* Interface index */
              unsigned int   ifi_flags;  /* Device flags  */
              unsigned int   ifi_change; /* change mask */

          ifi_flags contains the device flags, see netdevice(7); ifi_index
          is  the  unique interface index (since Linux 3.7, it is possible
          to feed a nonzero  value  with  the  RTM_NEWLINK  message,  thus
          creating  a link with the given ifindex); ifi_change is reserved
          for future use and should be always set to 0xFFFFFFFF.

                             Routing attributes
          rta_type         value type         description
          IFLA_UNSPEC      -                  unspecified.

          IFLA_ADDRESS     hardware address   interface L2 address
          IFLA_BROADCAST   hardware address   L2 broadcast address.
          IFLA_IFNAME      asciiz string      Device name.
          IFLA_MTU         unsigned int       MTU of the device.
          IFLA_LINK        int                Link type.
          IFLA_QDISC       asciiz string      Queueing discipline.
          IFLA_STATS       see below          Interface Statistics.

          The value type for IFLA_STATS is struct rtnl_link_stats  (struct
          net_device_stats in Linux 2.4 and earlier).

          Add,   remove   or  receive  information  about  an  IP  address
          associated with an interface.  In Linux 2.2,  an  interface  can
          carry  multiple  IP  addresses,  this  replaces the alias device
          concept in 2.0.  In Linux 2.2, these messages support  IPv4  and
          IPv6 addresses.  They contain an ifaddrmsg structure, optionally
          followed by rtattr routing attributes.

          struct ifaddrmsg {
              unsigned char ifa_family;    /* Address type */
              unsigned char ifa_prefixlen; /* Prefixlength of address */
              unsigned char ifa_flags;     /* Address flags */
              unsigned char ifa_scope;     /* Address scope */
              int           ifa_index;     /* Interface index */

          ifa_family is the address  family  type  (currently  AF_INET  or
          AF_INET6),  ifa_prefixlen  is  the length of the address mask of
          the address if defined for the family (like for IPv4), ifa_scope
          is  the  address  scope, ifa_index is the interface index of the
          interface the address is associated with.  ifa_flags is  a  flag
          word   of  IFA_F_SECONDARY  for  secondary  address  (old  alias
          interface), IFA_F_PERMANENT for a permanent address set  by  the
          user and other undocumented flags.

          rta_type        value type             description
          IFA_UNSPEC      -                      unspecified.
          IFA_ADDRESS     raw protocol address   interface address
          IFA_LOCAL       raw protocol address   local address
          IFA_LABEL       asciiz string          name of the interface
          IFA_BROADCAST   raw protocol address   broadcast address.
          IFA_ANYCAST     raw protocol address   anycast address
          IFA_CACHEINFO   struct ifa_cacheinfo   Address information.

          Create,  remove  or  receive  information about a network route.
          These messages contain  an  rtmsg  structure  with  an  optional
          sequence  of  rtattr  structures  following.   For RTM_GETROUTE,
          setting rtm_dst_len and rtm_src_len  to  0  means  you  get  all
          entries  for the specified routing table.  For the other fields,
          except rtm_table and rtm_protocol, 0 is the wildcard.

          struct rtmsg {
              unsigned char rtm_family;   /* Address family of route */
              unsigned char rtm_dst_len;  /* Length of destination */
              unsigned char rtm_src_len;  /* Length of source */
              unsigned char rtm_tos;      /* TOS filter */

              unsigned char rtm_table;    /* Routing table ID */
              unsigned char rtm_protocol; /* Routing protocol; see below */
              unsigned char rtm_scope;    /* See below */
              unsigned char rtm_type;     /* See below */

              unsigned int  rtm_flags;

          rtm_type          Route type
          RTN_UNSPEC        unknown route
          RTN_UNICAST       a gateway or direct route
          RTN_LOCAL         a local interface route
          RTN_BROADCAST     a  local  broadcast  route  (sent  as  a
          RTN_ANYCAST       a  local  broadcast  route  (sent  as  a
          RTN_MULTICAST     a multicast route
          RTN_BLACKHOLE     a packet dropping route
          RTN_UNREACHABLE   an unreachable destination
          RTN_PROHIBIT      a packet rejection route
          RTN_THROW         continue routing lookup in another table
          RTN_NAT           a network address translation rule
          RTN_XRESOLVE      refer  to  an  external  resolver   (not

          rtm_protocol      Route origin.
          RTPROT_UNSPEC     unknown
          RTPROT_REDIRECT   by    an   ICMP   redirect
                            (currently unused)
          RTPROT_KERNEL     by the kernel
          RTPROT_BOOT       during boot
          RTPROT_STATIC     by the administrator

          Values larger than RTPROT_STATIC  are  not  interpreted  by  the
          kernel, they are just for user information.  They may be used to
          tag the source  of  a  routing  information  or  to  distinguish
          between  multiple  routing daemons.  See <linux/rtnetlink.h> for
          the routing daemon identifiers which are already assigned.

          rtm_scope is the distance to the destination:

          RT_SCOPE_UNIVERSE   global route
          RT_SCOPE_SITE       interior  route   in   the
                              local autonomous system
          RT_SCOPE_LINK       route on this link
          RT_SCOPE_HOST       route on the local host
          RT_SCOPE_NOWHERE    destination doesn't exist

          The  values  between  RT_SCOPE_UNIVERSE  and  RT_SCOPE_SITE  are
          available to the user.

          The rtm_flags have the following meanings:

          RTM_F_NOTIFY     if the route changes, notify the  user  via
          RTM_F_CLONED     route is cloned from another route
          RTM_F_EQUALIZE   a multipath equalizer (not yet implemented)

          rtm_table specifies the routing table

          RT_TABLE_UNSPEC    an unspecified routing table
          RT_TABLE_DEFAULT   the default table
          RT_TABLE_MAIN      the main table
          RT_TABLE_LOCAL     the local table

          The user may assign arbitrary values between RT_TABLE_UNSPEC and

          rta_type        value type         description
          RTA_UNSPEC      -                  ignored.
          RTA_DST         protocol address   Route destination address.
          RTA_SRC         protocol address   Route source address.
          RTA_IIF         int                Input interface index.
          RTA_OIF         int                Output interface index.
          RTA_GATEWAY     protocol address   The gateway of the route
          RTA_PRIORITY    int                Priority of route.
          RTA_METRICS     int                Route metric

          Fill these values in!

          Add, remove or receive information about a neighbor table  entry
          (e.g., an ARP entry).  The message contains an ndmsg structure.

          struct ndmsg {
              unsigned char ndm_family;
              int           ndm_ifindex;  /* Interface index */
              __u16         ndm_state;    /* State */
              __u8          ndm_flags;    /* Flags */
              __u8          ndm_type;

          struct nda_cacheinfo {
              __u32         ndm_confirmed;
              __u32         ndm_used;
              __u32         ndm_updated;
              __u32         ndm_refcnt;

          ndm_state is a bit mask of the following states:

          NUD_INCOMPLETE   a currently resolving cache entry
          NUD_REACHABLE    a confirmed working cache entry
          NUD_STALE        an expired cache entry
          NUD_DELAY        an entry waiting for a timer
          NUD_PROBE        a cache entry that is currently reprobed
          NUD_FAILED       an invalid cache entry
          NUD_NOARP        a device with no destination cache
          NUD_PERMANENT    a static entry

          Valid ndm_flags are:

          NTF_PROXY    a proxy arp entry
          NTF_ROUTER   an IPv6 router

          The  rtattr  struct  has the following meanings for the rta_type

          NDA_UNSPEC      unknown type
          NDA_DST         a neighbor cache n/w layer destination address
          NDA_LLADDR      a neighbor cache link layer address
          NDA_CACHEINFO   cache statistics.

          If  the  rta_type  field  is  NDA_CACHEINFO,   then   a   struct
          nda_cacheinfo header follows

          Add, delete or retrieve a routing rule.  Carries a struct rtmsg

          Add,  remove or get a queueing discipline.  The message contains
          a struct tcmsg and may be followed by a series of attributes.

          struct tcmsg {
              unsigned char    tcm_family;
              int              tcm_ifindex;   /* interface index */
              __u32            tcm_handle;    /* Qdisc handle */
              __u32            tcm_parent;    /* Parent qdisc */
              __u32            tcm_info;

          rta_type     value type           Description
          TCA_UNSPEC   -                    unspecified
          TCA_KIND     asciiz string        Name of queueing discipline
          TCA_OPTIONS  byte sequence        Qdisc-specific options follow
          TCA_STATS    struct tc_stats      Qdisc statistics.
          TCA_XSTATS   qdisc-specific       Module-specific statistics.
          TCA_RATE     struct tc_estimator  Rate limit.

          In addition, various other qdisc-module-specific attributes  are
          allowed.   For  more  information  see  the  appropriate include

          Add, remove or get a traffic class.  These  messages  contain  a
          struct tcmsg as described above.

          Add,  remove  or  receive  information  about  a traffic filter.
          These messages contain a struct tcmsg as described above.


   rtnetlink is a new feature of Linux 2.2.


   This manual page is incomplete.


   cmsg(3), rtnetlink(3), ip(7), netlink(7)


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at

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