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 IFLA_PERM_ADDRESS hardware address hardware address
74 provided by device
75 (since Linux 5.5)
76 The value type for IFLA_STATS is struct rtnl_link_stats (struct
78 net_device_stats in Linux 2.4 and earlier).
79 RTM_NEWADDR, RTM_DELADDR, RTM_GETADDR
81 Add, remove, or receive information about an IP address associ‐
82 ated with an interface. In Linux 2.2, an interface can carry
83 multiple IP addresses, this replaces the alias device concept in
84 Linux 2.0. In Linux 2.2, these messages support IPv4 and IPv6
85 addresses. They contain an ifaddrmsg structure, optionally fol‐
86 lowed by rtattr routing attributes.
87 struct ifaddrmsg {
89 unsigned char ifa_family; /* Address type */
90 unsigned char ifa_prefixlen; /* Prefixlength of address */
91 unsigned char ifa_flags; /* Address flags */
92 unsigned char ifa_scope; /* Address scope */
93 unsigned int ifa_index; /* Interface index */
94 };
95 ifa_family is the address family type (currently AF_INET or
97 AF_INET6), ifa_prefixlen is the length of the address mask of
98 the address if defined for the family (like for IPv4), ifa_scope
99 is the address scope, ifa_index is the interface index of the
100 interface the address is associated with. ifa_flags is a flag
101 word of IFA_F_SECONDARY for secondary address (old alias inter‐
102 face), IFA_F_PERMANENT for a permanent address set by the user
103 and other undocumented flags.
104 Attributes
106 rta_type Value type Description
107 ─────────────────────────────────────────────────────────────
108 IFA_UNSPEC - unspecified
109 IFA_ADDRESS raw protocol address interface address
110 IFA_LOCAL raw protocol address local address
111 IFA_LABEL asciiz string name of the interface
112 IFA_BROADCAST raw protocol address broadcast address
113 IFA_ANYCAST raw protocol address anycast address
114 IFA_CACHEINFO struct ifa_cacheinfo Address information
115 RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
117 Create, remove, or receive information about a network route.
118 These messages contain an rtmsg structure with an optional se‐
119 quence of rtattr structures following. For RTM_GETROUTE, set‐
120 ting rtm_dst_len and rtm_src_len to 0 means you get all entries
121 for the specified routing table. For the other fields, except
122 rtm_table and rtm_protocol, 0 is the wildcard.
123 struct rtmsg {
125 unsigned char rtm_family; /* Address family of route */
126 unsigned char rtm_dst_len; /* Length of destination */
127 unsigned char rtm_src_len; /* Length of source */
128 unsigned char rtm_tos; /* TOS filter */
129 unsigned char rtm_table; /* Routing table ID;
130 see RTA_TABLE below */
131 unsigned char rtm_protocol; /* Routing protocol; see below */
132 unsigned char rtm_scope; /* See below */
133 unsigned char rtm_type; /* See below */
134 unsigned int rtm_flags;
136 };
137 rtm_type Route type
139 ───────────────────────────────────────────────────────────
140 RTN_UNSPEC unknown route
141 RTN_UNICAST a gateway or direct route
142 RTN_LOCAL a local interface route
143 RTN_BROADCAST a local broadcast route (sent as a
144 broadcast)
145 RTN_ANYCAST a local broadcast route (sent as a uni‐
146 cast)
147 RTN_MULTICAST a multicast route
148 RTN_BLACKHOLE a packet dropping route
149 RTN_UNREACHABLE an unreachable destination
150 RTN_PROHIBIT a packet rejection route
151 RTN_THROW continue routing lookup in another table
152 RTN_NAT a network address translation rule
153 RTN_XRESOLVE refer to an external resolver (not im‐
154 plemented)
155 rtm_protocol Route origin
157 ─────────────────────────────────────────────
158 RTPROT_UNSPEC unknown
159 RTPROT_REDIRECT by an ICMP redirect (cur‐
160 rently unused)
161 RTPROT_KERNEL by the kernel
162 RTPROT_BOOT during boot
163 RTPROT_STATIC by the administrator
164 Values larger than RTPROT_STATIC are not interpreted by the ker‐
166 nel, they are just for user information. They may be used to
167 tag the source of a routing information or to distinguish be‐
168 tween multiple routing daemons. See <linux/rtnetlink.h> for the
169 routing daemon identifiers which are already assigned.
170 rtm_scope is the distance to the destination:
172 RT_SCOPE_UNIVERSE global route
174 RT_SCOPE_SITE interior route in the lo‐
175 cal autonomous system
176 RT_SCOPE_LINK route on this link
177 RT_SCOPE_HOST route on the local host
178 RT_SCOPE_NOWHERE destination doesn't exist
179 The values between RT_SCOPE_UNIVERSE and RT_SCOPE_SITE are
181 available to the user.
182 The rtm_flags have the following meanings:
184 RTM_F_NOTIFY if the route changes, notify the user via
186 rtnetlink
187 RTM_F_CLONED route is cloned from another route
188 RTM_F_EQUALIZE a multipath equalizer (not yet implemented)
189 rtm_table specifies the routing table
191 RT_TABLE_UNSPEC an unspecified routing table
193 RT_TABLE_DEFAULT the default table
194 RT_TABLE_MAIN the main table
195 RT_TABLE_LOCAL the local table
196 The user may assign arbitrary values between RT_TABLE_UNSPEC and
198 RT_TABLE_DEFAULT.
199 Attributes
200 rta_type Value type Description
201 ────────────────────────────────────────────────────────────────
202 RTA_UNSPEC - ignored
203 RTA_DST protocol address Route destination address
204 RTA_SRC protocol address Route source address
205 RTA_IIF int Input interface index
206 RTA_OIF int Output interface index
207 RTA_GATEWAY protocol address The gateway of the route
208 RTA_PRIORITY int Priority of route
209 RTA_PREFSRC protocol address Preferred source address
210 RTA_METRICS int Route metric
211 RTA_MULTIPATH Multipath nexthop data br
212 (see below).
213 RTA_PROTOINFO No longer used
214 RTA_FLOW int Route realm
215 RTA_CACHEINFO struct rta_cacheinfo (see linux/rtnetlink.h)
216 RTA_SESSION No longer used
217 RTA_MP_ALGO No longer used
218 RTA_TABLE int Routing table ID; if set,
219 rtm_table is ignored
220 RTA_MARK int
221 RTA_MFC_STATS struct rta_mfc_stats (see linux/rtnetlink.h)
222 RTA_VIA struct rtvia Gateway in different AF
223 (see below)
224 RTA_NEWDST protocol address Change packet destination
225 address
226 RTA_PREF char RFC4191 IPv6 router pref‐
227 erence (see below)
228 RTA_ENCAP_TYPE short Encapsulation type for
229 lwtunnels (see below)
230 RTA_ENCAP Defined by RTA_ENCAP_TYPE
231 RTA_EXPIRES int Expire time for IPv6
232 routes (in seconds)
233 RTA_MULTIPATH contains several packed instances of struct rtnex‐
234 thop together with nested RTAs (RTA_GATEWAY):
235 struct rtnexthop {
237 unsigned short rtnh_len; /* Length of struct + length
238 of RTAs */
239 unsigned char rtnh_flags; /* Flags (see
240 linux/rtnetlink.h) */
241 unsigned char rtnh_hops; /* Nexthop priority */
242 int rtnh_ifindex; /* Interface index for this
243 nexthop */
244 }
245 There exist a bunch of RTNH_* macros similar to RTA_* and NL‐
247 HDR_* macros useful to handle these structures.
248 struct rtvia {
250 unsigned short rtvia_family;
251 unsigned char rtvia_addr[0];
252 };
253 rtvia_addr is the address, rtvia_family is its family type.
255 RTA_PREF may contain values ICMPV6_ROUTER_PREF_LOW,
257 ICMPV6_ROUTER_PREF_MEDIUM, and ICMPV6_ROUTER_PREF_HIGH defined
258 incw <linux/icmpv6.h>.
259 RTA_ENCAP_TYPE may contain values LWTUNNEL_ENCAP_MPLS, LWTUN‐
261 NEL_ENCAP_IP, LWTUNNEL_ENCAP_ILA, or LWTUNNEL_ENCAP_IP6 defined
262 in <linux/lwtunnel.h>.
263 Fill these values in!
265 RTM_NEWNEIGH, RTM_DELNEIGH, RTM_GETNEIGH
267 Add, remove, or receive information about a neighbor table entry
268 (e.g., an ARP entry). The message contains an ndmsg structure.
269 struct ndmsg {
271 unsigned char ndm_family;
272 int ndm_ifindex; /* Interface index */
273 __u16 ndm_state; /* State */
274 __u8 ndm_flags; /* Flags */
275 __u8 ndm_type;
276 };
277 struct nda_cacheinfo {
279 __u32 ndm_confirmed;
280 __u32 ndm_used;
281 __u32 ndm_updated;
282 __u32 ndm_refcnt;
283 };
284 ndm_state is a bit mask of the following states:
286 NUD_INCOMPLETE a currently resolving cache entry
288 NUD_REACHABLE a confirmed working cache entry
290 NUD_STALE an expired cache entry
291 NUD_DELAY an entry waiting for a timer
292 NUD_PROBE a cache entry that is currently reprobed
293 NUD_FAILED an invalid cache entry
295 NUD_NOARP a device with no destination cache
296 NUD_PERMANENT a static entry
297 Valid ndm_flags are:
299 NTF_PROXY a proxy arp entry
301 NTF_ROUTER an IPv6 router
302 The rtattr struct has the following meanings for the rta_type
304 field:
305 NDA_UNSPEC unknown type
307 NDA_DST a neighbor cache n/w layer destination address
308 NDA_LLADDR a neighbor cache link layer address
310 NDA_CACHEINFO cache statistics
311 If the rta_type field is NDA_CACHEINFO, then a struct nda_cache‐
313 info header follows.
314 RTM_NEWRULE, RTM_DELRULE, RTM_GETRULE
316 Add, delete, or retrieve a routing rule. Carries a struct rtmsg
317 RTM_NEWQDISC, RTM_DELQDISC, RTM_GETQDISC
319 Add, remove, or get a queueing discipline. The message contains
320 a struct tcmsg and may be followed by a series of attributes.
321 struct tcmsg {
323 unsigned char tcm_family;
324 int tcm_ifindex; /* interface index */
325 __u32 tcm_handle; /* Qdisc handle */
326 __u32 tcm_parent; /* Parent qdisc */
327 __u32 tcm_info;
328 };
329 Attributes
331 rta_type Value type Description
332 ────────────────────────────────────────────────────────────────
333 TCA_UNSPEC - unspecified
334 TCA_KIND asciiz string Name of queueing discipline
336 TCA_OPTIONS byte sequence Qdisc-specific options follow
337 TCA_STATS struct tc_stats Qdisc statistics
338 TCA_XSTATS qdisc-specific Module-specific statistics
339 TCA_RATE struct tc_estimator Rate limit
340 In addition, various other qdisc-module-specific attributes are
342 allowed. For more information see the appropriate include
343 files.
344 RTM_NEWTCLASS, RTM_DELTCLASS, RTM_GETTCLASS
346 Add, remove, or get a traffic class. These messages contain a
347 struct tcmsg as described above.
348 RTM_NEWTFILTER, RTM_DELTFILTER, RTM_GETTFILTER
350 Add, remove, or receive information about a traffic filter.
351 These messages contain a struct tcmsg as described above.
352
354 rtnetlink is a new feature of Linux 2.2.
355
357 This manual page is incomplete.
358
360 cmsg(3), rtnetlink(3), ip(7), netlink(7)
361Linux man-pages 6.05 2023-07-15 rtnetlink(7)