# rtnetlink

## NAME



           rtnetlink - Linux routing socket
    


## SYNOPSIS



           **#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



           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).
    
       **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 (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).
    
           **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 Linux 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.
                                           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
    
                  struct ifa_cacheinfo {
                      __u32 ifa_prefered; // Preferred lifetime remaining, in seconds
                      __u32 ifa_valid;    // Valid lifetime remaining, in seconds
                      __u32 cstamp;       // Creation timestamp, in centiseconds
                      __u32 tstamp;       // Update timestamp, in centiseconds
                  };
    
                  _ifa_valid_ cannot be zero, and _ifa_prefered_ cannot be
                  greater than _ifa_valid_.  A value of **UINT32_MAX** represents
                  an infinite lifetime.
    
           **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 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
                                    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 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**.
                                            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** 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
                                                        address
                  **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!**
    
           **RTM_NEWNEIGH**
           **RTM_DELNEIGH**
           **RTM_GETNEIGH**
                  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.
    
           **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 incomplete.
    


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