1rtnetlink(7) Miscellaneous Information Manual rtnetlink(7)
2
6 rtnetlink - Linux routing socket
7
9 #include <asm/types.h>
10 #include <linux/netlink.h>
11 #include <linux/rtnetlink.h>
12 #include <sys/socket.h>
13 rtnetlink_socket = socket(AF_NETLINK, int socket_type, NETLINK_ROUTE);
15
17 Rtnetlink allows the kernel's routing tables to be read and altered.
18 It is used within the kernel to communicate between various subsystems,
19 though this usage is not documented here, and for communication with
20 user-space programs. Network routes, IP addresses, link parameters,
21 neighbor setups, queueing disciplines, traffic classes and packet clas‐
22 sifiers may all be controlled through NETLINK_ROUTE sockets. It is
23 based on netlink messages; see netlink(7) for more information.
24 Routing attributes
26 Some rtnetlink messages have optional attributes after the initial
27 header:
28 struct rtattr {
30 unsigned short rta_len; /* Length of option */
31 unsigned short rta_type; /* Type of option */
32 /* Data follows */
33 };
34 These attributes should be manipulated using only the RTA_* macros or
36 libnetlink, see rtnetlink(3).
37 Messages
39 Rtnetlink consists of these message types (in addition to standard
40 netlink messages):
41 RTM_NEWLINK, RTM_DELLINK, RTM_GETLINK
43 Create, remove, or get information about a specific network in‐
44 terface. These messages contain an ifinfomsg structure followed
45 by a series of rtattr structures.
46 struct ifinfomsg {
48 unsigned char ifi_family; /* AF_UNSPEC */
49 unsigned short ifi_type; /* Device type */
50 int ifi_index; /* Interface index */
51 unsigned int ifi_flags; /* Device flags */
52 unsigned int ifi_change; /* change mask */
53 };
54 ifi_flags contains the device flags, see netdevice(7); ifi_index
56 is the unique interface index (since Linux 3.7, it is possible
57 to feed a nonzero value with the RTM_NEWLINK message, thus cre‐
58 ating a link with the given ifindex); ifi_change is reserved for
59 future use and should be always set to 0xFFFFFFFF.
60 Routing attributes
62 rta_type Value type Description
63 ─────────────────────────────────────────────────────────
64 IFLA_UNSPEC - unspecified
65 IFLA_ADDRESS hardware address interface L2 address
66 IFLA_BROADCAST hardware address L2 broadcast address
68 IFLA_IFNAME asciiz string Device name
69 IFLA_MTU unsigned int MTU of the device
70 IFLA_LINK int Link type
71 IFLA_QDISC asciiz string Queueing discipline
72 IFLA_STATS see below Interface Statistics
73 The value type for IFLA_STATS is struct rtnl_link_stats (struct
75 net_device_stats in Linux 2.4 and earlier).
76 RTM_NEWADDR, RTM_DELADDR, RTM_GETADDR
78 Add, remove, or receive information about an IP address associ‐
79 ated with an interface. In Linux 2.2, an interface can carry
80 multiple IP addresses, this replaces the alias device concept in
81 Linux 2.0. In Linux 2.2, these messages support IPv4 and IPv6
82 addresses. They contain an ifaddrmsg structure, optionally fol‐
83 lowed by rtattr routing attributes.
84 struct ifaddrmsg {
86 unsigned char ifa_family; /* Address type */
87 unsigned char ifa_prefixlen; /* Prefixlength of address */
88 unsigned char ifa_flags; /* Address flags */
89 unsigned char ifa_scope; /* Address scope */
90 unsigned int ifa_index; /* Interface index */
91 };
92 ifa_family is the address family type (currently AF_INET or
94 AF_INET6), ifa_prefixlen is the length of the address mask of
95 the address if defined for the family (like for IPv4), ifa_scope
96 is the address scope, ifa_index is the interface index of the
97 interface the address is associated with. ifa_flags is a flag
98 word of IFA_F_SECONDARY for secondary address (old alias inter‐
99 face), IFA_F_PERMANENT for a permanent address set by the user
100 and other undocumented flags.
101 Attributes
103 rta_type Value type Description
104 ─────────────────────────────────────────────────────────────
105 IFA_UNSPEC - unspecified
106 IFA_ADDRESS raw protocol address interface address
107 IFA_LOCAL raw protocol address local address
108 IFA_LABEL asciiz string name of the interface
109 IFA_BROADCAST raw protocol address broadcast address
110 IFA_ANYCAST raw protocol address anycast address
111 IFA_CACHEINFO struct ifa_cacheinfo Address information
112 RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
114 Create, remove, or receive information about a network route.
115 These messages contain an rtmsg structure with an optional se‐
116 quence of rtattr structures following. For RTM_GETROUTE, set‐
117 ting rtm_dst_len and rtm_src_len to 0 means you get all entries
118 for the specified routing table. For the other fields, except
119 rtm_table and rtm_protocol, 0 is the wildcard.
120 struct rtmsg {
122 unsigned char rtm_family; /* Address family of route */
123 unsigned char rtm_dst_len; /* Length of destination */
124 unsigned char rtm_src_len; /* Length of source */
125 unsigned char rtm_tos; /* TOS filter */
126 unsigned char rtm_table; /* Routing table ID;
127 see RTA_TABLE below */
128 unsigned char rtm_protocol; /* Routing protocol; see below */
129 unsigned char rtm_scope; /* See below */
130 unsigned char rtm_type; /* See below */
131 unsigned int rtm_flags;
133 };
134 rtm_type Route type
136 ───────────────────────────────────────────────────────────
137 RTN_UNSPEC unknown route
138 RTN_UNICAST a gateway or direct route
139 RTN_LOCAL a local interface route
140 RTN_BROADCAST a local broadcast route (sent as a
141 broadcast)
142 RTN_ANYCAST a local broadcast route (sent as a uni‐
143 cast)
144 RTN_MULTICAST a multicast route
145 RTN_BLACKHOLE a packet dropping route
146 RTN_UNREACHABLE an unreachable destination
147 RTN_PROHIBIT a packet rejection route
148 RTN_THROW continue routing lookup in another table
149 RTN_NAT a network address translation rule
150 RTN_XRESOLVE refer to an external resolver (not im‐
151 plemented)
152 rtm_protocol Route origin
154 ─────────────────────────────────────────────
155 RTPROT_UNSPEC unknown
156 RTPROT_REDIRECT by an ICMP redirect (cur‐
157 rently unused)
158 RTPROT_KERNEL by the kernel
159 RTPROT_BOOT during boot
160 RTPROT_STATIC by the administrator
161 Values larger than RTPROT_STATIC are not interpreted by the ker‐
163 nel, they are just for user information. They may be used to
164 tag the source of a routing information or to distinguish be‐
165 tween multiple routing daemons. See <linux/rtnetlink.h> for the
166 routing daemon identifiers which are already assigned.
167 rtm_scope is the distance to the destination:
169 RT_SCOPE_UNIVERSE global route
171 RT_SCOPE_SITE interior route in the lo‐
172 cal autonomous system
173 RT_SCOPE_LINK route on this link
174 RT_SCOPE_HOST route on the local host
175 RT_SCOPE_NOWHERE destination doesn't exist
176 The values between RT_SCOPE_UNIVERSE and RT_SCOPE_SITE are
178 available to the user.
179 The rtm_flags have the following meanings:
181 RTM_F_NOTIFY if the route changes, notify the user via
183 rtnetlink
184 RTM_F_CLONED route is cloned from another route
185 RTM_F_EQUALIZE a multipath equalizer (not yet implemented)
186 rtm_table specifies the routing table
188 RT_TABLE_UNSPEC an unspecified routing table
190 RT_TABLE_DEFAULT the default table
191 RT_TABLE_MAIN the main table
192 RT_TABLE_LOCAL the local table
193 The user may assign arbitrary values between RT_TABLE_UNSPEC and
195 RT_TABLE_DEFAULT.
196 Attributes
198 rta_type Value type Description
199 ────────────────────────────────────────────────────────────────
200 RTA_UNSPEC - ignored
201 RTA_DST protocol address Route destination address
202 RTA_SRC protocol address Route source address
203 RTA_IIF int Input interface index
204 RTA_OIF int Output interface index
205 RTA_GATEWAY protocol address The gateway of the route
206 RTA_PRIORITY int Priority of route
207 RTA_PREFSRC protocol address Preferred source address
208 RTA_METRICS int Route metric
209 RTA_MULTIPATH Multipath nexthop data br
210 (see below).
211 RTA_PROTOINFO No longer used
212 RTA_FLOW int Route realm
213 RTA_CACHEINFO struct rta_cacheinfo (see linux/rtnetlink.h)
214 RTA_SESSION No longer used
215 RTA_MP_ALGO No longer used
216 RTA_TABLE int Routing table ID; if set,
217 rtm_table is ignored
218 RTA_MARK int
219 RTA_MFC_STATS struct rta_mfc_stats (see linux/rtnetlink.h)
220 RTA_VIA struct rtvia Gateway in different AF
221 (see below)
222 RTA_NEWDST protocol address Change packet destination
223 address
224 RTA_PREF char RFC4191 IPv6 router pref‐
225 erence (see below)
226 RTA_ENCAP_TYPE short Encapsulation type for
227 lwtunnels (see below)
228 RTA_ENCAP Defined by RTA_ENCAP_TYPE
229 RTA_EXPIRES int Expire time for IPv6
230 routes (in seconds)
231 RTA_MULTIPATH contains several packed instances of struct rtnex‐
233 thop together with nested RTAs (RTA_GATEWAY):
234 struct rtnexthop {
236 unsigned short rtnh_len; /* Length of struct + length
237 of RTAs */
238 unsigned char rtnh_flags; /* Flags (see
239 linux/rtnetlink.h) */
240 unsigned char rtnh_hops; /* Nexthop priority */
241 int rtnh_ifindex; /* Interface index for this
242 nexthop */
243 }
244 There exist a bunch of RTNH_* macros similar to RTA_* and NL‐
246 HDR_* macros useful to handle these structures.
247 struct rtvia {
249 unsigned short rtvia_family;
250 unsigned char rtvia_addr[0];
251 };
252 rtvia_addr is the address, rtvia_family is its family type.
254 RTA_PREF may contain values ICMPV6_ROUTER_PREF_LOW,
256 ICMPV6_ROUTER_PREF_MEDIUM, and ICMPV6_ROUTER_PREF_HIGH defined
257 incw <linux/icmpv6.h>.
258 RTA_ENCAP_TYPE may contain values LWTUNNEL_ENCAP_MPLS, LWTUN‐
260 NEL_ENCAP_IP, LWTUNNEL_ENCAP_ILA, or LWTUNNEL_ENCAP_IP6 defined
261 in <linux/lwtunnel.h>.
262 Fill these values in!
264 RTM_NEWNEIGH, RTM_DELNEIGH, RTM_GETNEIGH
266 Add, remove, or receive information about a neighbor table entry
267 (e.g., an ARP entry). The message contains an ndmsg structure.
268 struct ndmsg {
270 unsigned char ndm_family;
271 int ndm_ifindex; /* Interface index */
272 __u16 ndm_state; /* State */
273 __u8 ndm_flags; /* Flags */
274 __u8 ndm_type;
275 };
276 struct nda_cacheinfo {
278 __u32 ndm_confirmed;
279 __u32 ndm_used;
280 __u32 ndm_updated;
281 __u32 ndm_refcnt;
282 };
283 ndm_state is a bit mask of the following states:
285 NUD_INCOMPLETE a currently resolving cache entry
287 NUD_REACHABLE a confirmed working cache entry
288 NUD_STALE an expired cache entry
289 NUD_DELAY an entry waiting for a timer
290 NUD_PROBE a cache entry that is currently reprobed
291 NUD_FAILED an invalid cache entry
292 NUD_NOARP a device with no destination cache
293 NUD_PERMANENT a static entry
294 Valid ndm_flags are:
296 NTF_PROXY a proxy arp entry
298 NTF_ROUTER an IPv6 router
299 The rtattr struct has the following meanings for the rta_type
301 field:
302 NDA_UNSPEC unknown type
304 NDA_DST a neighbor cache n/w layer destination address
305 NDA_LLADDR a neighbor cache link layer address
306 NDA_CACHEINFO cache statistics
307 If the rta_type field is NDA_CACHEINFO, then a struct nda_cache‐
309 info header follows.
310 RTM_NEWRULE, RTM_DELRULE, RTM_GETRULE
312 Add, delete, or retrieve a routing rule. Carries a struct rtmsg
313 RTM_NEWQDISC, RTM_DELQDISC, RTM_GETQDISC
315 Add, remove, or get a queueing discipline. The message contains
316 a struct tcmsg and may be followed by a series of attributes.
317 struct tcmsg {
319 unsigned char tcm_family;
320 int tcm_ifindex; /* interface index */
321 __u32 tcm_handle; /* Qdisc handle */
322 __u32 tcm_parent; /* Parent qdisc */
323 __u32 tcm_info;
324 };
325 Attributes
327 rta_type Value type Description
328 ────────────────────────────────────────────────────────────────
329 TCA_UNSPEC - unspecified
330 TCA_KIND asciiz string Name of queueing discipline
331 TCA_OPTIONS byte sequence Qdisc-specific options follow
332 TCA_STATS struct tc_stats Qdisc statistics
333 TCA_XSTATS qdisc-specific Module-specific statistics
334 TCA_RATE struct tc_estimator Rate limit
335 In addition, various other qdisc-module-specific attributes are
337 allowed. For more information see the appropriate include
338 files.
339 RTM_NEWTCLASS, RTM_DELTCLASS, RTM_GETTCLASS
341 Add, remove, or get a traffic class. These messages contain a
342 struct tcmsg as described above.
343 RTM_NEWTFILTER, RTM_DELTFILTER, RTM_GETTFILTER
345 Add, remove, or receive information about a traffic filter.
346 These messages contain a struct tcmsg as described above.
347
349 rtnetlink is a new feature of Linux 2.2.
350
352 This manual page is incomplete.
353
355 cmsg(3), rtnetlink(3), ip(7), netlink(7)
356Linux man-pages 6.04 2022-12-15 rtnetlink(7)