'\" t

.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.

.\"

.\" %%%LICENSE_START(VERBATIM_ONE_PARA)

.\" Permission is granted to distribute possibly modified copies

.\" of this page provided the header is included verbatim,

.\" and in case of nontrivial modification author and date

.\" of the modification is added to the header.

.\" %%%LICENSE_END

.\"

.\" Based on the original comments from Alexey Kuznetsov, written with

.\" help from Matthew Wilcox.

.\" $Id: rtnetlink.7,v 1.8 2000/01/22 01:55:04 freitag Exp $

.\"

.TH RTNETLINK  7 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

rtnetlink \- Linux IPv4 routing socket

.SH SYNOPSIS

.B #include <asm/types.h>

.br

.B #include <linux/netlink.h>

.br

.B #include <linux/rtnetlink.h>

.br

.B #include <sys/socket.h>

.PP

.BI "rtnetlink_socket = socket(AF_NETLINK, int " socket_type ", NETLINK_ROUTE);"

.SH 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

.B NETLINK_ROUTE

sockets.

It is based on netlink messages; see

.BR netlink (7)

for more information.

.\" FIXME . ? all these macros could be moved to rtnetlink(3)

.SS Routing attributes

Some rtnetlink messages have optional attributes after the initial header:

.PP

.in +4n

.EX

struct rtattr {

    unsigned short rta_len;    /* Length of option */

    unsigned short rta_type;   /* Type of option */

    /* Data follows */

};

.EE

.in

.PP

These attributes should be manipulated using only the RTA_* macros

or libnetlink, see

.BR rtnetlink (3).

.SS Messages

Rtnetlink consists of these message types

(in addition to standard netlink messages):

.TP

.BR RTM_NEWLINK ", " RTM_DELLINK ", " RTM_GETLINK

Create, remove or get information about a specific network interface.

These messages contain an

.I ifinfomsg

structure followed by a series of

.I rtattr

structures.

.IP

.EX

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 */

};

.EE

.IP

.\" FIXME Document ifinfomsg.ifi_type

.I ifi_flags

contains the device flags, see

.BR netdevice (7);

.I ifi_index

is the unique interface index

(since Linux 3.7, it is possible to feed a nonzero value with the

.B RTM_NEWLINK

message, thus creating a link with the given

.IR ifindex );

.I ifi_change

is reserved for future use and should be always set to 0xFFFFFFFF.

.TS

tab(:);

c s s

l l l.

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:T{

see below

T}:Interface Statistics.

.TE

.PP

The value type for

.B IFLA_STATS

is

.IR "struct rtnl_link_stats"

.RI ( "struct net_device_stats"

in Linux 2.4 and earlier).

.TP

.BR 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

.I ifaddrmsg

structure, optionally followed by

.I rtattr

routing attributes.

.IP

.EX

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 */

};

.EE

.IP

.I ifa_family

is the address family type (currently

.B AF_INET

or

.BR AF_INET6 ),

.I ifa_prefixlen

is the length of the address mask of the address if defined for the

family (like for IPv4),

.I ifa_scope

is the address scope,

.I ifa_index

is the interface index of the interface the address is associated with.

.I ifa_flags

is a flag word of

.B IFA_F_SECONDARY

for secondary address (old alias interface),

.B IFA_F_PERMANENT

for a permanent address set by the user and other undocumented flags.

.TS

tab(:);

c s s

l l l.

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.

.TE

.\" FIXME Document struct ifa_cacheinfo

.TP

.BR RTM_NEWROUTE ", " RTM_DELROUTE ", " RTM_GETROUTE

Create, remove or receive information about a network route.

These messages contain an

.I rtmsg

structure with an optional sequence of

.I rtattr

structures following.

For

.BR RTM_GETROUTE ,

setting

.I rtm_dst_len

and

.I rtm_src_len

to 0 means you get all entries for the specified routing table.

For the other fields, except

.I rtm_table

and

.IR rtm_protocol ,

0 is the wildcard.

.IP

.EX

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;

};

.EE

.TS

tab(:);

l l.

rtm_type:Route type

_

RTN_UNSPEC:unknown route

RTN_UNICAST:a gateway or direct route

RTN_LOCAL:a local interface route

RTN_BROADCAST:T{

a local broadcast route (sent as a broadcast)

T}

RTN_ANYCAST:T{

a local broadcast route (sent as a unicast)

T}

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:T{

refer to an external resolver (not implemented)

T}

.TE

.TS

tab(:);

l l.

rtm_protocol:Route origin.

_

RTPROT_UNSPEC:unknown

RTPROT_REDIRECT:T{

by an ICMP redirect (currently unused)

T}

RTPROT_KERNEL:by the kernel

RTPROT_BOOT:during boot

RTPROT_STATIC:by the administrator

.TE

.sp 1

Values larger than

.B 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

.I <linux/rtnetlink.h>

for the routing daemon identifiers which are already assigned.

.IP

.I rtm_scope

is the distance to the destination:

.TS

tab(:);

l l.

RT_SCOPE_UNIVERSE:global route

RT_SCOPE_SITE:T{

interior route in the local autonomous system

T}

RT_SCOPE_LINK:route on this link

RT_SCOPE_HOST:route on the local host

RT_SCOPE_NOWHERE:destination doesn't exist

.TE

.sp 1

The values between

.B RT_SCOPE_UNIVERSE

and

.B RT_SCOPE_SITE

are available to the user.

.IP

The

.I rtm_flags

have the following meanings:

.TS

tab(:);

l l.

RTM_F_NOTIFY:T{

if the route changes, notify the user via rtnetlink

T}

RTM_F_CLONED:route is cloned from another route

RTM_F_EQUALIZE:a multipath equalizer (not yet implemented)

.TE

.sp 1

.I rtm_table

specifies the routing table

.TS

tab(:);

l l.

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

.TE

.sp 1

The user may assign arbitrary values between

.B RT_TABLE_UNSPEC

and

.BR RT_TABLE_DEFAULT .

.\" Keep table on same page

.bp +1

.TS

tab(:);

c s s

l l l.

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::

.TE

.sp 1

.B Fill these values in!

.TP

.BR 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

.I ndmsg

structure.

.IP

.EX

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;

};

.EE

.IP

.I ndm_state

is a bit mask of the following states:

.TS

tab(:);

l l.

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

.TE

.sp 1

Valid

.I ndm_flags

are:

.TS

tab(:);

l l.

NTF_PROXY:a proxy arp entry

NTF_ROUTER:an IPv6 router

.TE

.sp 1

.\" FIXME .

.\" document the members of the struct better

The

.I rtattr

struct has the following meanings for the

.I rta_type

field:

.TS

tab(:);

l l.

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.

.TE

.sp 1

If the

.I rta_type

field is

.BR NDA_CACHEINFO ,

then a

.I struct nda_cacheinfo

header follows

.TP

.BR RTM_NEWRULE ", " RTM_DELRULE ", " RTM_GETRULE

Add, delete or retrieve a routing rule.

Carries a

.I struct rtmsg

.TP

.BR RTM_NEWQDISC ", " RTM_DELQDISC ", " RTM_GETQDISC

Add, remove or get a queueing discipline.

The message contains a

.I struct tcmsg

and may be followed by a series of

attributes.

.IP

.EX

struct tcmsg {

    unsigned char    tcm_family;

    int              tcm_ifindex;   /* interface index */

    __u32            tcm_handle;    /* Qdisc handle */

    __u32            tcm_parent;    /* Parent qdisc */

    __u32            tcm_info;

};

.EE

.TS

tab(:);

c s s

l2 l2 l.

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.

.TE

.sp 1

In addition, various other qdisc-module-specific attributes are allowed.

For more information see the appropriate include files.

.TP

.BR RTM_NEWTCLASS ", " RTM_DELTCLASS ", " RTM_GETTCLASS

Add, remove or get a traffic class.

These messages contain a

.I struct tcmsg

as described above.

.TP

.BR RTM_NEWTFILTER ", " RTM_DELTFILTER ", " RTM_GETTFILTER

Add, remove or receive information about a traffic filter.

These messages contain a

.I struct tcmsg

as described above.

.SH VERSIONS

.B rtnetlink

is a new feature of Linux 2.2.

.SH BUGS

This manual page is incomplete.

.SH SEE ALSO

.BR cmsg (3),

.BR rtnetlink (3),

.BR ip (7),

.BR netlink (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.