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NAME

       rtnetlink, NETLINK_ROUTE - Linux IPv4 routing socket

SYNOPSIS

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

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

DESCRIPTION

       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,
       neighbour  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 only manipulated using the RTA_*  macros  or
       libnetlink, see rtnetlink(3).

MESSAGES

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

       RTM_NEWLINK, RTM_DELLINK, RTM_GETLINK
              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           struct             Interface Statistics.
                                   net_device_stats

       RTM_NEWADDR, RTM_DELADDR, RTM_GETADDR
              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 the 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.

               Attributes
              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.

       RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
              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 source */
                  unsigned char  rtm_src_len; /* Length of destination */
                  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
                                broadcast)
              RTN_ANYCAST       a  local  broadcast  route  (sent  as  a
                                unicast)
              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
                                implemented)

              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
                               rtnetlink
              RTM_F_CLONED     route is cloned from another route
              RTM_F_EQUALIZE   a multicast 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.

               Attributes
              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
              RTA_METRICS     int                Route metric
              RTA_MULTIPATH
              RTA_PROTOINFO
              RTA_FLOW
              RTA_CACHEINFO

              Fill these values in!

       RTM_NEWNEIGH, RTM_DELNEIGH, RTM_GETNEIGH
              Add, remove or receive information about a neighbour 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 bitmask 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

              document the members of the struct better

              The  rtaddr  struct  has the following meanings for the rta_type
              field:

              NDA_UNSPEC      unknown type
              NDA_DST         a neighbour cache network layer destination address
              NDA_LLADDR      a neighbour cache link layer address
              NDA_CACHEINFO   cache statistics.

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

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

       RTM_NEWQDISC, RTM_DELQDISC, RTM_GETQDISC
              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;
              };

              Attributes
              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.

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

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

VERSIONS

       rtnetlink is a new feature of Linux 2.2.

BUGS

       This manual page is lacking and incomplete.

SEE ALSO

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