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RTNETLINK(4) Device Drivers Manual RTNETLINK(4)

RTNetlink — Network configuration-specific Netlink family

#include <netlink/netlink.h>
#include <netlink/netlink_route.h>

int
socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);

The NETLINK_ROUTE family aims to be the primary configuration mechanism for all network-related tasks. Currently it supports configuring interfaces, interface addresses, routes, nexthops and arp/ndp neighbors.

All route configuration messages share the common header:

struct rtmsg {
	unsigned char	rtm_family;	/* address family */
	unsigned char	rtm_dst_len;	/* Prefix length */
	unsigned char	rtm_src_len;	/* Deprecated, set to 0 */
	unsigned char	rtm_tos;	/* Type of service (not used) */
	unsigned char	rtm_table;	/* deprecated, set to 0 */
	unsigned char	rtm_protocol;	/* Routing protocol id (RTPROT_) */
	unsigned char	rtm_scope;	/* Route distance (RT_SCOPE_) */
	unsigned char	rtm_type;	/* Route type (RTN_) */
	unsigned 	rtm_flags;	/* Route flags (not supported) */
};

The rtm_family specifies the route family to be operated on. Currently, AF_INET6 and AF_INET are the only supported families. The route prefix length is stored in rtm_dst_len The caller should set the originator identity (one of the RTPROT_ values) in rtm_protocol It is useful for users and for the application itself, allowing for easy identification of self-originated routes. The route scope has to be set via rtm_scope field. The supported values are:

RT_SCOPE_UNIVERSE	Global scope
RT_SCOPE_LINK		Link scope

Route type needs to be set. The defined values are:

RTN_UNICAST	Unicast route
RTN_MULTICAST	Multicast route
RTN_BLACKHOLE	Drops traffic towards destination
RTN_PROHIBIT	Drops traffic and sends reject

The following messages are supported:

Adds a new route. All NL flags are supported. Extending a multipath route requires NLM_F_APPEND flag.

Tries to delete a route. The route is specified using a combination of RTA_DST TLV and rtm_dst_len.

Fetches a single route or all routes in the current VNET, depending on the NLM_F_DUMP flag. Each route is reported as RTM_NEWROUTE message. The following filters are recognised by the kernel:

rtm_family	required family or AF_UNSPEC
RTA_TABLE	fib number or RT_TABLE_UNSPEC to return all fibs

(binary) IPv4/IPv6 address, depending on the rtm_family.
(uint32_t) transmit interface index.
(binary) IPv4/IPv6 gateway address, depending on the rtm_family.
(nested) Container attribute, listing route properties. The only supported sub-attribute is RTAX_MTU, which stores path MTU as uint32_t.
This attribute contains multipath route nexthops with their weights. These nexthops are represented as a sequence of rtnexthop structures, each followed by RTA_GATEWAY or RTA_VIA attributes. 
struct rtnexthop {
	unsigned short		rtnh_len;
	unsigned char		rtnh_flags;
	unsigned char		rtnh_hops;	/* nexthop weight */
	int			rtnh_ifindex;
};

The rtnh_len field specifies the total nexthop info length, including both struct rtnexthop and the following TLVs. The rtnh_hops field stores relative nexthop weight, used for load balancing between group members. The rtnh_ifindex field contains the index of the transmit interface.

The following TLVs can follow the structure:

RTA_GATEWAY	IPv4/IPv6 nexthop address of the gateway
RTA_VIA		IPv6 nexthop address for IPv4 route
RTA_KNH_ID	Kernel-specific index of the nexthop
(uint32_t) (FreeBSD-specific) Auto-allocated kernel index of the nexthop.
(uint32_t) (FreeBSD-specific) rtsock route flags.
(uint32_t) Fib number of the route. Default route table is RT_TABLE_MAIN. To explicitly specify "all tables" one needs to set the value to RT_TABLE_UNSPEC.
(uint32_t) seconds till path expiration.
(uint32_t) useland nexthop or nexthop group index.

The following groups are defined:

RTNLGRP_IPV4_ROUTE	Notifies on IPv4 route arrival/removal/change
RTNLGRP_IPV6_ROUTE	Notifies on IPv6 route arrival/removal/change

All nexthop/nexthop group configuration messages share the common header:

struct nhmsg {
        unsigned char	nh_family;	/* transport family */
	unsigned char	nh_scope;	/* ignored on RX, filled by kernel */
	unsigned char	nh_protocol;	/* Routing protocol that installed nh */
	unsigned char	resvd;
	unsigned int	nh_flags;	/* RTNH_F_* flags from route.h */
};
The nh_family specifies the gateway address family. It can be different from route address family for IPv4 routes with IPv6 nexthops. The nh_protocol is similar to rtm_protocol field, which designates originator application identity.

The following messages are supported:

Creates a new nexthop or nexthop group.

Deletes nexthop or nexthhop group. The required object is specified by the RTA_NH_ID attribute.

Fetches a single nexthop or all nexthops/nexthop groups, depending on the NLM_F_DUMP flag. The following filters are recognised by the kernel:

RTA_NH_ID	nexthop or nexthtop group id
NHA_GROUPS	match only nexthtop groups

(uint32_t) Nexthhop index used to identify particular nexthop or nexthop group. Should be provided by userland at the nexthtop creation time.
This attribute designates the nexthtop group and contains all of its nexthtops and their relative weights. The attribute consists of a list of nexthop_grp structures: 
struct nexthop_grp {
	uint32_t	id;		/* nexhop userland index */
	uint8_t		weight;         /* weight of this nexthop */
	uint8_t		resvd1;
	uint16_t	resvd2;
};
(uint16_t) Nexthtop group type, set to one of the following types: 
NEXTHOP_GRP_TYPE_MPATH	default multipath group
(flag) Marks the nexthtop as blackhole.
(uint32_t) Transmit interface index of the nexthtop.
(binary) IPv4/IPv6 gateway address
(flag) Matches nexthtop groups during dump.

The following groups are defined:

RTNLGRP_NEXTHOP		Notifies on nexthop/groups arrival/removal/change

All interface configuration messages share the common header:

struct ifinfomsg {
	unsigned char	ifi_family;	/* not used, set to 0 */
	unsigned char	__ifi_pad;
	unsigned short	ifi_type;	/* ARPHRD_* */
	int		ifi_index;	/* Interface index */
	unsigned	ifi_flags;	/* IFF_* flags */
	unsigned	ifi_change;	/* IFF_* change mask */
};

Creates a new interface. The only mandatory TLV is IFLA_IFNAME. The following attributes are returned inside the nested NLMSGERR_ATTR_COOKIE:

IFLA_NEW_IFINDEX	(uint32) created interface index
IFLA_IFNAME		(string) created interface name

Deletes the interface specified by IFLA_IFNAME.

Fetches a single interface or all interfaces in the current VNET, depending on the NLM_F_DUMP flag. Each interface is reported as a RTM_NEWLINK message. The following filters are recognised by the kernel:

ifi_index	interface index
IFLA_IFNAME	interface name
IFLA_ALT_IFNAME	interface name

(binary) Llink-level interface address (MAC).
(binary) (readonly) Link-level broadcast address.
(string) New interface name.
(string) Interface description.
(uint32_t) (readonly) Interface index.
(uint32_t) Parent interface index.
(nested) Interface type-specific attributes: 
IFLA_INFO_KIND		(string) interface type ("vlan")
IFLA_INFO_DATA		(nested) custom attributes
The following types and attributes are supported: 
IFLA_VLAN_ID		(uint16_t) 802.1Q vlan id
IFLA_VLAN_PROTOCOL	(uint16_t) Protocol: ETHERTYPE_VLAN or ETHERTYPE_QINQ
(uint8_t) Interface operational state per RFC 2863. Can be one of the following: 
IF_OPER_UNKNOWN		status can not be determined
IF_OPER_NOTPRESENT	some (hardware) component not present
IF_OPER_DOWN		down
IF_OPER_LOWERLAYERDOWN	some lower-level interface is down
IF_OPER_TESTING		in some test mode
IF_OPER_DORMANT		"up" but waiting for some condition (802.1X)
IF_OPER_UP		ready to pass packets
(readonly) Consists of the following 64-bit counters structure: 
struct rtnl_link_stats64 {
	uint64_t rx_packets;	/* total RX packets (IFCOUNTER_IPACKETS) */
	uint64_t tx_packets;	/* total TX packets (IFCOUNTER_OPACKETS) */
	uint64_t rx_bytes;	/* total RX bytes (IFCOUNTER_IBYTES) */
	uint64_t tx_bytes;	/* total TX bytes (IFCOUNTER_OBYTES) */
	uint64_t rx_errors;	/* RX errors (IFCOUNTER_IERRORS) */
	uint64_t tx_errors;	/* RX errors (IFCOUNTER_OERRORS) */
	uint64_t rx_dropped;	/* RX drop (no space in ring/no bufs) (IFCOUNTER_IQDROPS) */
	uint64_t tx_dropped;	/* TX drop (IFCOUNTER_OQDROPS) */
	uint64_t multicast;	/* RX multicast packets (IFCOUNTER_IMCASTS) */
	uint64_t collisions;	/* not supported */
	uint64_t rx_length_errors;	/* not supported */
	uint64_t rx_over_errors;	/* not supported */
	uint64_t rx_crc_errors;		/* not supported */
	uint64_t rx_frame_errors;	/* not supported */
	uint64_t rx_fifo_errors;	/* not supported */
	uint64_t rx_missed_errors;	/* not supported */
	uint64_t tx_aborted_errors;	/* not supported */
	uint64_t tx_carrier_errors;	/* not supported */
	uint64_t tx_fifo_errors;	/* not supported */
	uint64_t tx_heartbeat_errors;	/* not supported */
	uint64_t tx_window_errors;	/* not supported */
	uint64_t rx_compressed;		/* not supported */
	uint64_t tx_compressed;		/* not supported */
	uint64_t rx_nohandler;	/* dropped due to no proto handler (IFCOUNTER_NOPROTO) */
};

The following groups are defined:

RTNLGRP_LINK		Notifies on interface arrival/removal/change

All interface address configuration messages share the common header:

struct ifaddrmsg {
	uint8_t		ifa_family;	/* Address family */
	uint8_t		ifa_prefixlen;	/* Prefix length */
	uint8_t		ifa_flags;	/* Address-specific flags */
	uint8_t		ifa_scope;	/* Address scope */
	uint32_t	ifa_index;	/* Link ifindex */
};

The ifa_family specifies the address family of the interface address. The ifa_prefixlen specifies the prefix length if applicable for the address family. The ifa_index specifies the interface index of the target interface.

Not supported

Not supported

Fetches interface addresses in the current VNET matching conditions. Each address is reported as a RTM_NEWADDR message. The following filters are recognised by the kernel:

ifa_family	required family or AF_UNSPEC
ifa_index	matching interface index or 0

(binary) masked interface address or destination address for p2p interfaces.
(binary) local interface address. Set for IPv4 and p2p addresses.
(string) interface name.
(binary) broadcast interface address.

The following groups are defined:

RTNLGRP_IPV4_IFADDR	Notifies on IPv4 ifaddr arrival/removal/change
RTNLGRP_IPV6_IFADDR	Notifies on IPv6 ifaddr arrival/removal/change

All neighbor configuration messages share the common header:

struct ndmsg {
	uint8_t		ndm_family;
	uint8_t		ndm_pad1;
	uint16_t	ndm_pad2;
	int32_t		ndm_ifindex;
	uint16_t	ndm_state;
	uint8_t		ndm_flags;
	uint8_t		ndm_type;
};

The ndm_family field specifies the address family (IPv4 or IPv6) of the neighbor. The ndm_ifindex specifies the interface to operate on. The ndm_state represents the entry state according to the neighbor model. The state can be one of the following:

NUD_INCOMPLETE		No lladdr, address resolution in progress
NUD_REACHABLE		reachable & recently resolved
NUD_STALE		has lladdr but it's stale
NUD_DELAY		has lladdr, is stale, probes delayed
NUD_PROBE		has lladdr, is stale, probes sent
NUD_FAILED		unused

The ndm_flags field stores the options specific to this entry. Available flags:

NTF_SELF		local station (LLE_IFADDR)
NTF_PROXY		proxy entry (LLE_PUB)
NTF_STICKY		permanent entry (LLE_STATIC)
NTF_ROUTER		dst indicated itself as a router

Creates new neighbor entry. The mandatory options are NDA_DST, NDA_LLADDR and NDA_IFINDEX.

Deletes the neighbor entry. The entry is specified by the combination of NDA_DST and NDA_IFINDEX.

Fetches a single neighbor or all neighbors in the current VNET, depending on the NLM_F_DUMP flag. Each entry is reported as RTM_NEWNEIGH message. The following filters are recognised by the kernel:

ndm_family	required family or AF_UNSPEC
ndm_ifindex	target ifindex
NDA_IFINDEX	target ifindex

(binary) neighbor IPv4/IPv6 address.
(binary) neighbor link-level address.
(uint32_t) interface index.
(uint32_t) extended version of ndm_flags.

The following groups are defined:

RTNLGRP_NEIGH	Notifies on ARP/NDP neighbor  arrival/removal/change

netlink(4), route(4)

The NETLINK_ROUTE protocol family appeared in FreeBSD 13.2.

The netlink was implemented by Alexander Chernikov <melifaro@FreeBSD.org>. It was derived from the Google Summer of Code 2021 project by Ng Peng Nam Sean.

November 1, 2022 dev