rtnetlink(7) — Linux manual page


rtnetlink(7)        Miscellaneous Information Manual        rtnetlink(7)

NAME         top

       rtnetlink - Linux routing socket

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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(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
              IFLA_PERM_ADDRESS   hardware address   hardware address
                                                     provided by device
                                                     (since Linux 5.5)

              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 Linux 2.0.  In Linux 2.2, these messages
              support IPv4 and IPv6 addresses.  They contain an
              ifaddrmsg structure, optionally followed by rtattr routing

              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 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
              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

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

              RTA_ENCAP_TYPE may contain values LWTUNNEL_ENCAP_MPLS,
              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

              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

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

              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.

VERSIONS         top

       rtnetlink is a new feature of Linux 2.2.

BUGS         top

       This manual page is incomplete.

SEE ALSO         top

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

Linux man-pages (unreleased)     (date)                     rtnetlink(7)

Pages that refer to this page: libnetlink(3)rtnetlink(3)address_families(7)netdevice(7)netlink(7)