RTNETLINK(7)

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 net_device_stats | Interface Statistics.

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 distingush 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 arbitary 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)