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       rtnetlink, NETLINK_ROUTE - Linux IPv4 routing socket


       #include <asm/types.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 only manipulated using 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, 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 net_device_stats.

              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 rtaddr 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  rtaddr  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)


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