Manpage of RTNETLINK

RTNETLINK

Section: Linux Programmer's Manual (7)
Updated: 2013-03-05
Index
 

NAME

rtnetlink - Linux IPv4 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_ROUTEsockets. 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 ifinfomsgstructure followed by a series of rtattrstructures.

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_flagscontains the device flags, see netdevice(7); ifi_indexis the unique interface index (since Linux 3.7, it is possible to feed a nonzero value with the RTM_NEWLINKmessage, thus creating a link with the given ifindex); ifi_changeis reserved for future use and should be always set to 0xFFFFFFFF.

Routing attributes
rta_typevalue typedescription

IFLA_UNSPEC-unspecified.
IFLA_ADDRESShardware addressinterface L2 address
IFLA_BROADCASThardware addressL2 broadcast address.
IFLA_IFNAMEasciiz stringDevice name.
IFLA_MTUunsigned intMTU of the device.
IFLA_LINKintLink type.
IFLA_QDISCasciiz stringQueueing discipline.
IFLA_STATSsee below Interface Statistics.

The value type for IFLA_STATSis struct rtnl_link_stats(struct net_device_statsin 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 2.0. In Linux 2.2, these messages support IPv4 and IPv6 addresses. They contain an ifaddrmsgstructure, optionally followed by rtattrrouting 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_familyis the address family type (currently AF_INETor AF_INET6), ifa_prefixlenis the length of the address mask of the address if defined for the family (like for IPv4), ifa_scopeis the address scope, ifa_indexis the interface index of the interface the address is associated with. ifa_flagsis a flag word of IFA_F_SECONDARYfor secondary address (old alias interface), IFA_F_PERMANENTfor a permanent address set by the user and other undocumented flags.

Attributes
rta_typevalue typedescription

IFA_UNSPEC-unspecified.
IFA_ADDRESSraw protocol addressinterface address
IFA_LOCALraw protocol addresslocal address
IFA_LABELasciiz stringname of the interface
IFA_BROADCASTraw protocol addressbroadcast address.
IFA_ANYCASTraw protocol addressanycast address
IFA_CACHEINFOstruct ifa_cacheinfoAddress information.
RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
Create, remove or receive information about a network route. These messages contain an rtmsgstructure with an optional sequence of rtattrstructures following. For RTM_GETROUTE, setting rtm_dst_lenand rtm_src_lento 0 means you get all entries for the specified routing table. For the other fields, except rtm_tableand 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_typeRoute type

RTN_UNSPECunknown route
RTN_UNICASTa gateway or direct route
RTN_LOCALa local interface route
RTN_BROADCASTa local broadcast route (sent as a broadcast)
RTN_ANYCASTa local broadcast route (sent as a unicast)
RTN_MULTICASTa multicast route
RTN_BLACKHOLEa packet dropping route
RTN_UNREACHABLEan unreachable destination
RTN_PROHIBITa packet rejection route
RTN_THROWcontinue routing lookup in another table
RTN_NATa network address translation rule
RTN_XRESOLVErefer to an external resolver (not implemented)
rtm_protocolRoute origin.

RTPROT_UNSPECunknown
RTPROT_REDIRECTby an ICMP redirect (currently unused)
RTPROT_KERNELby the kernel
RTPROT_BOOTduring boot
RTPROT_STATICby the administrator

Values larger than RTPROT_STATICare 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_scopeis the distance to the destination:

RT_SCOPE_UNIVERSEglobal route
RT_SCOPE_SITEinterior route in the local autonomous system
RT_SCOPE_LINKroute on this link
RT_SCOPE_HOSTroute on the local host
RT_SCOPE_NOWHEREdestination doesn't exist

The values between RT_SCOPE_UNIVERSEand RT_SCOPE_SITEare available to the user.

The rtm_flagshave the following meanings:

RTM_F_NOTIFYif the route changes, notify the user via rtnetlink
RTM_F_CLONEDroute is cloned from another route
RTM_F_EQUALIZEa multipath equalizer (not yet implemented)

rtm_tablespecifies the routing table

RT_TABLE_UNSPECan unspecified routing table
RT_TABLE_DEFAULTthe default table
RT_TABLE_MAINthe main table
RT_TABLE_LOCALthe local table

The user may assign arbitrary values between RT_TABLE_UNSPECand RT_TABLE_DEFAULT.

Attributes
rta_typevalue typedescription

RTA_UNSPEC-ignored.
RTA_DSTprotocol addressRoute destination address.
RTA_SRCprotocol addressRoute source address.
RTA_IIFintInput interface index.
RTA_OIFintOutput interface index.
RTA_GATEWAYprotocol addressThe gateway of the route
RTA_PRIORITYintPriority of route.
RTA_PREFSRC
RTA_METRICSintRoute 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 neighbor table entry (e.g., an ARP entry). The message contains an ndmsgstructure.

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_stateis a bit mask of the following states:

NUD_INCOMPLETEa currently resolving cache entry
NUD_REACHABLEa confirmed working cache entry
NUD_STALEan expired cache entry
NUD_DELAYan entry waiting for a timer
NUD_PROBEa cache entry that is currently reprobed
NUD_FAILEDan invalid cache entry
NUD_NOARPa device with no destination cache
NUD_PERMANENTa static entry

Valid ndm_flagsare:

NTF_PROXYa proxy arp entry
NTF_ROUTERan IPv6 router

The rtattrstruct has the following meanings for the rta_typefield:

NDA_UNSPECunknown type
NDA_DSTa neighbor cache n/w layer destination address
NDA_LLADDRa neighbor cache link layer address
NDA_CACHEINFOcache statistics.

If the rta_typefield is NDA_CACHEINFO, then a struct nda_cacheinfoheader 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 tcmsgand 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 tcmsgas described above.
RTM_NEWTFILTER, RTM_DELTFILTER, RTM_GETTFILTER
Add, remove or receive information about a traffic filter. These messages contain a struct tcmsgas described above.
 

VERSIONS

rtnetlinkis a new feature of Linux 2.2.  

BUGS

This manual page is incomplete.  

SEE ALSO

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


 

Index

NAME
SYNOPSIS
DESCRIPTION
Routing attributes
Messages
VERSIONS
BUGS
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 22:28:03 GMT, June 20, 2016