man7/rtnetlink.7

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   2 .\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
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  10 .\"
  11 .\" Based on the original comments from Alexey Kuznetsov, written with
  12 .\" help from Matthew Wilcox.
  13 .\" $Id: rtnetlink.7,v 1.8 2000/01/22 01:55:04 freitag Exp $
  14 .\"
  15 .TH RTNETLINK  7 2020-02-09 "Linux" "Linux Programmer's Manual"
  16 .SH NAME
  17 rtnetlink \- Linux IPv4 routing socket
  18 .SH SYNOPSIS
  19 .B #include <asm/types.h>
  20 .br
  21 .B #include <linux/netlink.h>
  22 .br
  23 .B #include <linux/rtnetlink.h>
  24 .br
  25 .B #include <sys/socket.h>
  26 .PP
  27 .BI "rtnetlink_socket = socket(AF_NETLINK, int " socket_type ", NETLINK_ROUTE);"
  28 .SH DESCRIPTION
  29 Rtnetlink allows the kernel's routing tables to be read and altered.
  30 It is used within the kernel to communicate between
  31 various subsystems, though this usage is not documented here, and for
  32 communication with user-space programs.
  33 Network routes, IP addresses, link parameters, neighbor setups, queueing
  34 disciplines, traffic classes and packet classifiers may all be controlled
  35 through
  36 .B NETLINK_ROUTE
  37 sockets.
  38 It is based on netlink messages; see
  39 .BR netlink (7)
  40 for more information.
  41 .\" FIXME . ? all these macros could be moved to rtnetlink(3)
  42 .SS Routing attributes
  43 Some rtnetlink messages have optional attributes after the initial header:
  44 .PP
  45 .in +4n
  46 .EX
  47 struct rtattr {
  48     unsigned short rta_len;    /* Length of option */
  49     unsigned short rta_type;   /* Type of option */
  50     /* Data follows */
  51 };
  52 .EE
  53 .in
  54 .PP
  55 These attributes should be manipulated using only the RTA_* macros
  56 or libnetlink, see
  57 .BR rtnetlink (3).
  58 .SS Messages
  59 Rtnetlink consists of these message types
  60 (in addition to standard netlink messages):
  61 .TP
  62 .BR RTM_NEWLINK ", " RTM_DELLINK ", " RTM_GETLINK
  63 Create, remove or get information about a specific network interface.
  64 These messages contain an
  65 .I ifinfomsg
  66 structure followed by a series of
  67 .I rtattr
  68 structures.
  69 .IP
  70 .EX
  71 struct ifinfomsg {
  72     unsigned char  ifi_family; /* AF_UNSPEC */
  73     unsigned short ifi_type;   /* Device type */
  74     int            ifi_index;  /* Interface index */
  75     unsigned int   ifi_flags;  /* Device flags  */
  76     unsigned int   ifi_change; /* change mask */
  77 };
  78 .EE
  79 .IP
  80 .\" FIXME Document ifinfomsg.ifi_type
  81 .I ifi_flags
  82 contains the device flags, see
  83 .BR netdevice (7);
  84 .I ifi_index
  85 is the unique interface index
  86 (since Linux 3.7, it is possible to feed a nonzero value with the
  87 .B RTM_NEWLINK
  88 message, thus creating a link with the given
  89 .IR ifindex );
  90 .I ifi_change
  91 is reserved for future use and should be always set to 0xFFFFFFFF.
  92 .TS
  93 tab(:);
  94 c s s
  95 l l l.
  96 Routing attributes
  97 rta_type:value type:description
  98 _
  99 IFLA_UNSPEC:-:unspecified.
 100 IFLA_ADDRESS:hardware address:interface L2 address
 101 IFLA_BROADCAST:hardware address:L2 broadcast address.
 102 IFLA_IFNAME:asciiz string:Device name.
 103 IFLA_MTU:unsigned int:MTU of the device.
 104 IFLA_LINK:int:Link type.
 105 IFLA_QDISC:asciiz string:Queueing discipline.
 106 IFLA_STATS:T{
 107 see below
 108 T}:Interface Statistics.
 109 .TE
 110 .PP
 111 The value type for
 112 .B IFLA_STATS
 113 is
 114 .IR "struct rtnl_link_stats"
 115 .RI ( "struct net_device_stats"
 116 in Linux 2.4 and earlier).
 117 .TP
 118 .BR RTM_NEWADDR ", " RTM_DELADDR ", " RTM_GETADDR
 119 Add, remove or receive information about an IP address associated with
 120 an interface.
 121 In Linux 2.2, an interface can carry multiple IP addresses,
 122 this replaces the alias device concept in 2.0.
 123 In Linux 2.2, these messages
 124 support IPv4 and IPv6 addresses.
 125 They contain an
 126 .I ifaddrmsg
 127 structure, optionally followed by
 128 .I rtattr
 129 routing attributes.
 130 .IP
 131 .EX
 132 struct ifaddrmsg {
 133     unsigned char ifa_family;    /* Address type */
 134     unsigned char ifa_prefixlen; /* Prefixlength of address */
 135     unsigned char ifa_flags;     /* Address flags */
 136     unsigned char ifa_scope;     /* Address scope */
 137     unsigned int  ifa_index;     /* Interface index */
 138 };
 139 .EE
 140 .IP
 141 .I ifa_family
 142 is the address family type (currently
 143 .B AF_INET
 144 or
 145 .BR AF_INET6 ),
 146 .I ifa_prefixlen
 147 is the length of the address mask of the address if defined for the
 148 family (like for IPv4),
 149 .I ifa_scope
 150 is the address scope,
 151 .I ifa_index
 152 is the interface index of the interface the address is associated with.
 153 .I ifa_flags
 154 is a flag word of
 155 .B IFA_F_SECONDARY
 156 for secondary address (old alias interface),
 157 .B IFA_F_PERMANENT
 158 for a permanent address set by the user and other undocumented flags.
 159 .TS
 160 tab(:);
 161 c s s
 162 l l l.
 163 Attributes
 164 rta_type:value type:description
 165 _
 166 IFA_UNSPEC:-:unspecified.
 167 IFA_ADDRESS:raw protocol address:interface address
 168 IFA_LOCAL:raw protocol address:local address
 169 IFA_LABEL:asciiz string:name of the interface
 170 IFA_BROADCAST:raw protocol address:broadcast address.
 171 IFA_ANYCAST:raw protocol address:anycast address
 172 IFA_CACHEINFO:struct ifa_cacheinfo:Address information.
 173 .TE
 174 .\" FIXME Document struct ifa_cacheinfo
 175 .TP
 176 .BR RTM_NEWROUTE ", " RTM_DELROUTE ", " RTM_GETROUTE
 177 Create, remove or receive information about a network route.
 178 These messages contain an
 179 .I rtmsg
 180 structure with an optional sequence of
 181 .I rtattr
 182 structures following.
 183 For
 184 .BR RTM_GETROUTE ,
 185 setting
 186 .I rtm_dst_len
 187 and
 188 .I rtm_src_len
 189 to 0 means you get all entries for the specified routing table.
 190 For the other fields, except
 191 .I rtm_table
 192 and
 193 .IR rtm_protocol ,
 194 0 is the wildcard.
 195 .IP
 196 .EX
 197 struct rtmsg {
 198     unsigned char rtm_family;   /* Address family of route */
 199     unsigned char rtm_dst_len;  /* Length of destination */
 200     unsigned char rtm_src_len;  /* Length of source */
 201     unsigned char rtm_tos;      /* TOS filter */
 202
 203     unsigned char rtm_table;    /* Routing table ID; see RTA_TABLE below */
 204     unsigned char rtm_protocol; /* Routing protocol; see below */
 205     unsigned char rtm_scope;    /* See below */
 206     unsigned char rtm_type;     /* See below */
 207
 208     unsigned int  rtm_flags;
 209 };
 210 .EE
 211 .TS
 212 tab(:);
 213 l l.
 214 rtm_type:Route type
 215 _
 216 RTN_UNSPEC:unknown route
 217 RTN_UNICAST:a gateway or direct route
 218 RTN_LOCAL:a local interface route
 219 RTN_BROADCAST:T{
 220 a local broadcast route (sent as a broadcast)
 221 T}
 222 RTN_ANYCAST:T{
 223 a local broadcast route (sent as a unicast)
 224 T}
 225 RTN_MULTICAST:a multicast route
 226 RTN_BLACKHOLE:a packet dropping route
 227 RTN_UNREACHABLE:an unreachable destination
 228 RTN_PROHIBIT:a packet rejection route
 229 RTN_THROW:continue routing lookup in another table
 230 RTN_NAT:a network address translation rule
 231 RTN_XRESOLVE:T{
 232 refer to an external resolver (not implemented)
 233 T}
 234 .TE
 235 .TS
 236 tab(:);
 237 l l.
 238 rtm_protocol:Route origin.
 239 _
 240 RTPROT_UNSPEC:unknown
 241 RTPROT_REDIRECT:T{
 242 by an ICMP redirect (currently unused)
 243 T}
 244 RTPROT_KERNEL:by the kernel
 245 RTPROT_BOOT:during boot
 246 RTPROT_STATIC:by the administrator
 247 .TE
 248 .sp 1
 249 Values larger than
 250 .B RTPROT_STATIC
 251 are not interpreted by the kernel, they are just for user information.
 252 They may be used to tag the source of a routing information or to
 253 distinguish between multiple routing daemons.
 254 See
 255 .I <linux/rtnetlink.h>
 256 for the routing daemon identifiers which are already assigned.
 257 .IP
 258 .I rtm_scope
 259 is the distance to the destination:
 260 .TS
 261 tab(:);
 262 l l.
 263 RT_SCOPE_UNIVERSE:global route
 264 RT_SCOPE_SITE:T{
 265 interior route in the local autonomous system
 266 T}
 267 RT_SCOPE_LINK:route on this link
 268 RT_SCOPE_HOST:route on the local host
 269 RT_SCOPE_NOWHERE:destination doesn't exist
 270 .TE
 271 .sp 1
 272 The values between
 273 .B RT_SCOPE_UNIVERSE
 274 and
 275 .B RT_SCOPE_SITE
 276 are available to the user.
 277 .IP
 278 The
 279 .I rtm_flags
 280 have the following meanings:
 281 .TS
 282 tab(:);
 283 l l.
 284 RTM_F_NOTIFY:T{
 285 if the route changes, notify the user via rtnetlink
 286 T}
 287 RTM_F_CLONED:route is cloned from another route
 288 RTM_F_EQUALIZE:a multipath equalizer (not yet implemented)
 289 .TE
 290 .sp 1
 291 .I rtm_table
 292 specifies the routing table
 293 .TS
 294 tab(:);
 295 l l.
 296 RT_TABLE_UNSPEC:an unspecified routing table
 297 RT_TABLE_DEFAULT:the default table
 298 RT_TABLE_MAIN:the main table
 299 RT_TABLE_LOCAL:the local table
 300 .TE
 301 .sp 1
 302 The user may assign arbitrary values between
 303 .B RT_TABLE_UNSPEC
 304 and
 305 .BR RT_TABLE_DEFAULT .
 306 .\" Keep table on same page
 307 .bp +1
 308 .TS
 309 tab(:);
 310 c s s
 311 l l l.
 312 Attributes
 313 rta_type:value type:description
 314 _
 315 RTA_UNSPEC:-:ignored.
 316 RTA_DST:protocol address:Route destination address.
 317 RTA_SRC:protocol address:Route source address.
 318 RTA_IIF:int:Input interface index.
 319 RTA_OIF:int:Output interface index.
 320 RTA_GATEWAY:protocol address:The gateway of the route
 321 RTA_PRIORITY:int:Priority of route.
 322 RTA_PREFSRC:protocol address:Preferred source address.
 323 RTA_METRICS:int:Route metric
 324 RTA_MULTIPATH::Multipath nexthop data (see below).
 325 RTA_PROTOINFO::No longer used
 326 RTA_FLOW:int:Route realm
 327 RTA_CACHEINFO:struct rta_cacheinfo:(see linux/rtnetlink.h)
 328 RTA_SESSION::No longer used
 329 RTA_MP_ALGO::No longer used
 330 RTA_TABLE:int:Routing table ID; if set, rtm_table is ignored.
 331 RTA_MARK:int:
 332 RTA_MFC_STATS:struct rta_mfc_stats:(see linux/rtnetlink.h)
 333 RTA_VIA:struct rtvia:Gateway in different AF (see below).
 334 RTA_NEWDST:protocol address:Change packet destination address.
 335 RTA_PREF:char:RFC4191 IPv6 router preference (see below).
 336 RTA_ENCAP_TYPE:short:Encapsulation type for lwtunnels (see below).
 337 RTA_ENCAP::Defined by RTA_ENCAP_TYPE.
 338 RTA_EXPIRES:int:Expire time for IPv6 routes (in seconds).
 339 .TE
 340 .I RTA_MULTIPATH
 341 contains several packed instances of
 342 .I struct rtnexthop
 343 together with nested RTA's (RTA_GATEWAY)
 344
 345 .nf
 346 struct rtnexthop {
 347     unsigned short  rtnh_len;       /* Length of struct + length of RTA's
 348     unsigned char   rtnh_flags;     /* Flags (see linux/rtnetlink.h) */
 349     unsigned char   rtnh_hops;      /* Nexthop priority */
 350     int             rtnh_ifindex;   /* Interface index for this nexthop */
 351 }
 352
 353 There exist a bunch of RTNH_* macros similar to RTA_* and NLHDR_* macros
 354 useful to handle these structures.
 355
 356 .nf
 357 struct rtvia {
 358     unsigned short rtvia_family;
 359     unsigned char  rtvia_addr[0];
 360 };
 361 .fi
 362
 363 .I rtvia_addr
 364 is the address,
 365 .I rtvia_family
 366 is its family type.
 367
 368 .I RTA_PREF
 369 may contain values ICMPV6_ROUTER_PREF_LOW,
 370 ICMPV6_ROUTER_PREF_MEDIUM and
 371 ICMPV6_ROUTER_PREF_HIGH defined in <linux/icmpv6.h>
 372
 373 .I RTA_ENCAP_TYPE
 374 may contain values LWTUNNEL_ENCAP_MPLS, LWTUNNEL_ENCAP_IP, LWTUNNEL_ENCAP_ILA or LWTUNNEL_ENCAP_IP6
 375 defined in <linux/lwtunnel.h>
 376 .sp 1
 377 .B Fill these values in!
 378 .TP
 379 .BR RTM_NEWNEIGH ", " RTM_DELNEIGH  ", " RTM_GETNEIGH
 380 Add, remove or receive information about a neighbor table
 381 entry (e.g., an ARP entry).
 382 The message contains an
 383 .I ndmsg
 384 structure.
 385 .IP
 386 .EX
 387 struct ndmsg {
 388     unsigned char ndm_family;
 389     int           ndm_ifindex;  /* Interface index */
 390     __u16         ndm_state;    /* State */
 391     __u8          ndm_flags;    /* Flags */
 392     __u8          ndm_type;
 393 };
 394
 395 struct nda_cacheinfo {
 396     __u32         ndm_confirmed;
 397     __u32         ndm_used;
 398     __u32         ndm_updated;
 399     __u32         ndm_refcnt;
 400 };
 401 .EE
 402 .IP
 403 .I ndm_state
 404 is a bit mask of the following states:
 405 .TS
 406 tab(:);
 407 l l.
 408 NUD_INCOMPLETE:a currently resolving cache entry
 409 NUD_REACHABLE:a confirmed working cache entry
 410 NUD_STALE:an expired cache entry
 411 NUD_DELAY:an entry waiting for a timer
 412 NUD_PROBE:a cache entry that is currently reprobed
 413 NUD_FAILED:an invalid cache entry
 414 NUD_NOARP:a device with no destination cache
 415 NUD_PERMANENT:a static entry
 416 .TE
 417 .sp 1
 418 Valid
 419 .I ndm_flags
 420 are:
 421 .TS
 422 tab(:);
 423 l l.
 424 NTF_PROXY:a proxy arp entry
 425 NTF_ROUTER:an IPv6 router
 426 .TE
 427 .sp 1
 428 .\" FIXME .
 429 .\" document the members of the struct better
 430 The
 431 .I rtattr
 432 struct has the following meanings for the
 433 .I rta_type
 434 field:
 435 .TS
 436 tab(:);
 437 l l.
 438 NDA_UNSPEC:unknown type
 439 NDA_DST:a neighbor cache n/w layer destination address
 440 NDA_LLADDR:a neighbor cache link layer address
 441 NDA_CACHEINFO:cache statistics.
 442 .TE
 443 .sp 1
 444 If the
 445 .I rta_type
 446 field is
 447 .BR NDA_CACHEINFO ,
 448 then a
 449 .I struct nda_cacheinfo
 450 header follows
 451 .TP
 452 .BR RTM_NEWRULE ", " RTM_DELRULE ", " RTM_GETRULE
 453 Add, delete or retrieve a routing rule.
 454 Carries a
 455 .I struct rtmsg
 456 .TP
 457 .BR RTM_NEWQDISC ", " RTM_DELQDISC ", " RTM_GETQDISC
 458 Add, remove or get a queueing discipline.
 459 The message contains a
 460 .I struct tcmsg
 461 and may be followed by a series of
 462 attributes.
 463 .IP
 464 .EX
 465 struct tcmsg {
 466     unsigned char    tcm_family;
 467     int              tcm_ifindex;   /* interface index */
 468     __u32            tcm_handle;    /* Qdisc handle */
 469     __u32            tcm_parent;    /* Parent qdisc */
 470     __u32            tcm_info;
 471 };
 472 .EE
 473 .TS
 474 tab(:);
 475 c s s
 476 l2 l2 l.
 477 Attributes
 478 rta_type:value type:Description
 479 _
 480 TCA_UNSPEC:-:unspecified
 481 TCA_KIND:asciiz string:Name of queueing discipline
 482 TCA_OPTIONS:byte sequence:Qdisc-specific options follow
 483 TCA_STATS:struct tc_stats:Qdisc statistics.
 484 TCA_XSTATS:qdisc-specific:Module-specific statistics.
 485 TCA_RATE:struct tc_estimator:Rate limit.
 486 .TE
 487 .sp 1
 488 In addition, various other qdisc-module-specific attributes are allowed.
 489 For more information see the appropriate include files.
 490 .TP
 491 .BR RTM_NEWTCLASS ", " RTM_DELTCLASS ", " RTM_GETTCLASS
 492 Add, remove or get a traffic class.
 493 These messages contain a
 494 .I struct tcmsg
 495 as described above.
 496 .TP
 497 .BR RTM_NEWTFILTER ", " RTM_DELTFILTER ", " RTM_GETTFILTER
 498 Add, remove or receive information about a traffic filter.
 499 These messages contain a
 500 .I struct tcmsg
 501 as described above.
 502 .SH VERSIONS
 503 .B rtnetlink
 504 is a new feature of Linux 2.2.
 505 .SH BUGS
 506 This manual page is incomplete.
 507 .SH SEE ALSO
 508 .BR cmsg (3),
 509 .BR rtnetlink (3),
 510 .BR ip (7),
 511 .BR netlink (7)