# RTNETLINK(7) - man - phpMan [RTNETLINK(7)](https://www.chedong.com/phpMan.php/man/RTNETLINK/7/markdown) Linux Programmer's Manual [RTNETLINK(7)](https://www.chedong.com/phpMan.php/man/RTNETLINK/7/markdown) ## NAME rtnetlink - Linux IPv4 routing socket ## SYNOPSIS ### #include **#include** **** ### #include ### #include ### #include **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 parame‐ ters, 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)](https://www.chedong.com/phpMan.php/man/netlink/7/markdown) 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 **rt**‐‐ [**netlink**(3)](https://www.chedong.com/phpMan.php/man/netlink/3/markdown). ### 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)](https://www.chedong.com/phpMan.php/man/netdevice/7/markdown); _ifi_index_ is the unique inter‐ face 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 re‐ served 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 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 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 inter‐ face 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 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 uni‐ cast) **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 im‐ plemented) **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 __ 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 au‐ tonomous 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 pref‐ erence (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 __. **RTA**___**ENCAP**___**TYPE** may contain values **LWTUNNEL**___**ENCAP**___**MPLS**, **LWTUNNEL**___**ENCAP**___**IP**, **LWTUNNEL**___**EN**‐‐ **CAP**___**ILA**, or **LWTUNNEL**___**ENCAP**___**IP6** defined in __. **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 in‐ formation 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 de‐ scribed 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. ## SEE ALSO [**cmsg**(3)](https://www.chedong.com/phpMan.php/man/cmsg/3/markdown), [**rtnetlink**(3)](https://www.chedong.com/phpMan.php/man/rtnetlink/3/markdown), [**ip**(7)](https://www.chedong.com/phpMan.php/man/ip/7/markdown), [**netlink**(7)](https://www.chedong.com/phpMan.php/man/netlink/7/markdown) ## COLOPHON This page is part of release 5.10 of the Linux _man-pages_ project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at . Linux 2020-06-09 [RTNETLINK(7)](https://www.chedong.com/phpMan.php/man/RTNETLINK/7/markdown)