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       rtnetlink - Linux 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 header:

           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 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 */
                  unsigned 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;
                                                 see RTA_TABLE below */
                  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
              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 RT_TABLE_DEFAULT.

              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_PREFSRC     protocol address      Preferred source address
              RTA_METRICS     int                   Route metric
              RTA_MULTIPATH                         Multipath nexthop data br
                                                    (see below).
              RTA_PROTOINFO                         No longer used
              RTA_FLOW        int                   Route realm
              RTA_CACHEINFO   struct rta_cacheinfo  (see linux/rtnetlink.h)
              RTA_SESSION                           No longer used
              RTA_MP_ALGO                           No longer used
              RTA_TABLE       int                   Routing table ID; if set,
                                                    rtm_table is ignored
              RTA_MARK        int
              RTA_MFC_STATS   struct rta_mfc_stats  (see linux/rtnetlink.h)
              RTA_VIA         struct rtvia          Gateway  in  different AF
                                                    (see below)
              RTA_NEWDST      protocol address      Change packet destination
              RTA_PREF        char                  RFC4191    IPv6    router
                                                    preference (see below)
              RTA_ENCAP_TYPE  short                 Encapsulation type for
                                                    lwtunnels (see below)
              RTA_ENCAP                             Defined by RTA_ENCAP_TYPE
              RTA_EXPIRES     int                   Expire  time   for   IPv6
                                                    routes (in seconds)

              RTA_MULTIPATH  contains  several packed instances of struct rtnexthop together with
              nested RTAs (RTA_GATEWAY):

                  struct rtnexthop {
                      unsigned short rtnh_len;     /* Length of struct + length
                                                      of RTAs */
                      unsigned char  rtnh_flags;   /* Flags (see
                                                      linux/rtnetlink.h) */
                      unsigned char  rtnh_hops;    /* Nexthop priority */
                      int            rtnh_ifindex; /* Interface index for this
                                                      nexthop */

              There exist a bunch of RTNH_* macros similar to RTA_* and NLHDR_* macros useful  to
              handle these structures.

                  struct rtvia {
                      unsigned short rtvia_family;
                      unsigned char  rtvia_addr[0];

              rtvia_addr is the address, rtvia_family is its family type.

              RTA_PREF  may contain values ICMPV6_ROUTER_PREF_LOW, ICMPV6_ROUTER_PREF_MEDIUM, and
              ICMPV6_ROUTER_PREF_HIGH defined incw <linux/icmpv6.h>.

              RTA_ENCAP_TYPE   may   contain   values   LWTUNNEL_ENCAP_MPLS,   LWTUNNEL_ENCAP_IP,
              LWTUNNEL_ENCAP_ILA, or LWTUNNEL_ENCAP_IP6 defined in <linux/lwtunnel.h>.

              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 field:

              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 files.

              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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