man7/rtnetlink.7

   1 .\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
   2 .\"
   3 .\" %%%LICENSE_START(VERBATIM_ONE_PARA)
   4 .\" Permission is granted to distribute possibly modified copies
   5 .\" of this page provided the header is included verbatim,
   6 .\" and in case of nontrivial modification author and date
   7 .\" of the modification is added to the header.
   8 .\" %%%LICENSE_END
   9 .\"
  10 .\" Based on the original comments from Alexey Kuznetsov, written with
  11 .\" help from Matthew Wilcox.
  12 .\" $Id: rtnetlink.7,v 1.8 2000/01/22 01:55:04 freitag Exp $
  13 .\"
  14 .TH RTNETLINK  7 2021-03-22 "Linux" "Linux Programmer's Manual"
  15 .SH NAME
  16 rtnetlink \- Linux routing socket
  17 .SH SYNOPSIS
  18 .nf
  19 .B #include <asm/types.h>
  20 .B #include <linux/netlink.h>
  21 .B #include <linux/rtnetlink.h>
  22 .B #include <sys/socket.h>
  23 .PP
  24 .BI "rtnetlink_socket = socket(AF_NETLINK, int " socket_type ", NETLINK_ROUTE);"
  25 .fi
  26 .SH DESCRIPTION
  27 Rtnetlink allows the kernel's routing tables to be read and altered.
  28 It is used within the kernel to communicate between
  29 various subsystems, though this usage is not documented here, and for
  30 communication with user-space programs.
  31 Network routes, IP addresses, link parameters, neighbor setups, queueing
  32 disciplines, traffic classes and packet classifiers may all be controlled
  33 through
  34 .B NETLINK_ROUTE
  35 sockets.
  36 It is based on netlink messages; see
  37 .BR netlink (7)
  38 for more information.
  39 .\" FIXME . ? all these macros could be moved to rtnetlink(3)
  40 .SS Routing attributes
  41 Some rtnetlink messages have optional attributes after the initial header:
  42 .PP
  43 .in +4n
  44 .EX
  45 struct rtattr {
  46     unsigned short rta_len;    /* Length of option */
  47     unsigned short rta_type;   /* Type of option */
  48     /* Data follows */
  49 };
  50 .EE
  51 .in
  52 .PP
  53 These attributes should be manipulated using only the RTA_* macros
  54 or libnetlink, see
  55 .BR rtnetlink (3).
  56 .SS Messages
  57 Rtnetlink consists of these message types
  58 (in addition to standard netlink messages):
  59 .TP
  60 .BR RTM_NEWLINK ", " RTM_DELLINK ", " RTM_GETLINK
  61 Create, remove, or get information about a specific network interface.
  62 These messages contain an
  63 .I ifinfomsg
  64 structure followed by a series of
  65 .I rtattr
  66 structures.
  67 .IP
  68 .EX
  69 struct ifinfomsg {
  70     unsigned char  ifi_family; /* AF_UNSPEC */
  71     unsigned short ifi_type;   /* Device type */
  72     int            ifi_index;  /* Interface index */
  73     unsigned int   ifi_flags;  /* Device flags  */
  74     unsigned int   ifi_change; /* change mask */
  75 };
  76 .EE
  77 .IP
  78 .\" FIXME Document ifinfomsg.ifi_type
  79 .I ifi_flags
  80 contains the device flags, see
  81 .BR netdevice (7);
  82 .I ifi_index
  83 is the unique interface index
  84 (since Linux 3.7, it is possible to feed a nonzero value with the
  85 .B RTM_NEWLINK
  86 message, thus creating a link with the given
  87 .IR ifindex );
  88 .I ifi_change
  89 is reserved for future use and should be always set to 0xFFFFFFFF.
  90 .TS
  91 tab(:);
  92 c s s
  93 lb l l.
  94 Routing attributes
  95 rta_type:Value type:Description
  96 _
  97 IFLA_UNSPEC:-:unspecified
  98 IFLA_ADDRESS:hardware address:interface L2 address
  99 IFLA_BROADCAST:hardware address:L2 broadcast address
 100 IFLA_IFNAME:asciiz string:Device name
 101 IFLA_MTU:unsigned int:MTU of the device
 102 IFLA_LINK:int:Link type
 103 IFLA_QDISC:asciiz string:Queueing discipline
 104 IFLA_STATS:T{
 105 see below
 106 T}:Interface Statistics
 107 .TE
 108 .IP
 109 The value type for
 110 .B IFLA_STATS
 111 is
 112 .IR "struct rtnl_link_stats"
 113 .RI ( "struct net_device_stats"
 114 in Linux 2.4 and earlier).
 115 .TP
 116 .BR RTM_NEWADDR ", " RTM_DELADDR ", " RTM_GETADDR
 117 Add, remove, or receive information about an IP address associated with
 118 an interface.
 119 In Linux 2.2, an interface can carry multiple IP addresses,
 120 this replaces the alias device concept in 2.0.
 121 In Linux 2.2, these messages
 122 support IPv4 and IPv6 addresses.
 123 They contain an
 124 .I ifaddrmsg
 125 structure, optionally followed by
 126 .I rtattr
 127 routing attributes.
 128 .IP
 129 .EX
 130 struct ifaddrmsg {
 131     unsigned char ifa_family;    /* Address type */
 132     unsigned char ifa_prefixlen; /* Prefixlength of address */
 133     unsigned char ifa_flags;     /* Address flags */
 134     unsigned char ifa_scope;     /* Address scope */
 135     unsigned int  ifa_index;     /* Interface index */
 136 };
 137 .EE
 138 .IP
 139 .I ifa_family
 140 is the address family type (currently
 141 .B AF_INET
 142 or
 143 .BR AF_INET6 ),
 144 .I ifa_prefixlen
 145 is the length of the address mask of the address if defined for the
 146 family (like for IPv4),
 147 .I ifa_scope
 148 is the address scope,
 149 .I ifa_index
 150 is the interface index of the interface the address is associated with.
 151 .I ifa_flags
 152 is a flag word of
 153 .B IFA_F_SECONDARY
 154 for secondary address (old alias interface),
 155 .B IFA_F_PERMANENT
 156 for a permanent address set by the user and other undocumented flags.
 157 .TS
 158 tab(:);
 159 c s s
 160 lb l l.
 161 Attributes
 162 rta_type:Value type:Description
 163 _
 164 IFA_UNSPEC:-:unspecified
 165 IFA_ADDRESS:raw protocol address:interface address
 166 IFA_LOCAL:raw protocol address:local address
 167 IFA_LABEL:asciiz string:name of the interface
 168 IFA_BROADCAST:raw protocol address:broadcast address
 169 IFA_ANYCAST:raw protocol address:anycast address
 170 IFA_CACHEINFO:struct ifa_cacheinfo:Address information
 171 .TE
 172 .\" FIXME Document struct ifa_cacheinfo
 173 .TP
 174 .BR RTM_NEWROUTE ", " RTM_DELROUTE ", " RTM_GETROUTE
 175 Create, remove, or receive information about a network route.
 176 These messages contain an
 177 .I rtmsg
 178 structure with an optional sequence of
 179 .I rtattr
 180 structures following.
 181 For
 182 .BR RTM_GETROUTE ,
 183 setting
 184 .I rtm_dst_len
 185 and
 186 .I rtm_src_len
 187 to 0 means you get all entries for the specified routing table.
 188 For the other fields, except
 189 .I rtm_table
 190 and
 191 .IR rtm_protocol ,
 192 0 is the wildcard.
 193 .IP
 194 .EX
 195 struct rtmsg {
 196     unsigned char rtm_family;   /* Address family of route */
 197     unsigned char rtm_dst_len;  /* Length of destination */
 198     unsigned char rtm_src_len;  /* Length of source */
 199     unsigned char rtm_tos;      /* TOS filter */
 200     unsigned char rtm_table;    /* Routing table ID;
 201                                    see RTA_TABLE below */
 202     unsigned char rtm_protocol; /* Routing protocol; see below */
 203     unsigned char rtm_scope;    /* See below */
 204     unsigned char rtm_type;     /* See below */
 205
 206     unsigned int  rtm_flags;
 207 };
 208 .EE
 209 .TS
 210 tab(:);
 211 lb l.
 212 rtm_type:Route type
 213 _
 214 RTN_UNSPEC:unknown route
 215 RTN_UNICAST:a gateway or direct route
 216 RTN_LOCAL:a local interface route
 217 RTN_BROADCAST:T{
 218 a local broadcast route (sent as a broadcast)
 219 T}
 220 RTN_ANYCAST:T{
 221 a local broadcast route (sent as a unicast)
 222 T}
 223 RTN_MULTICAST:a multicast route
 224 RTN_BLACKHOLE:a packet dropping route
 225 RTN_UNREACHABLE:an unreachable destination
 226 RTN_PROHIBIT:a packet rejection route
 227 RTN_THROW:continue routing lookup in another table
 228 RTN_NAT:a network address translation rule
 229 RTN_XRESOLVE:T{
 230 refer to an external resolver (not implemented)
 231 T}
 232 .TE
 233 .TS
 234 tab(:);
 235 lb l.
 236 rtm_protocol:Route origin
 237 _
 238 RTPROT_UNSPEC:unknown
 239 RTPROT_REDIRECT:T{
 240 by an ICMP redirect (currently unused)
 241 T}
 242 RTPROT_KERNEL:by the kernel
 243 RTPROT_BOOT:during boot
 244 RTPROT_STATIC:by the administrator
 245 .TE
 246 .sp 1
 247 Values larger than
 248 .B RTPROT_STATIC
 249 are not interpreted by the kernel, they are just for user information.
 250 They may be used to tag the source of a routing information or to
 251 distinguish between multiple routing daemons.
 252 See
 253 .I <linux/rtnetlink.h>
 254 for the routing daemon identifiers which are already assigned.
 255 .IP
 256 .I rtm_scope
 257 is the distance to the destination:
 258 .TS
 259 tab(:);
 260 lb l.
 261 RT_SCOPE_UNIVERSE:global route
 262 RT_SCOPE_SITE:T{
 263 interior route in the local autonomous system
 264 T}
 265 RT_SCOPE_LINK:route on this link
 266 RT_SCOPE_HOST:route on the local host
 267 RT_SCOPE_NOWHERE:destination doesn't exist
 268 .TE
 269 .sp 1
 270 The values between
 271 .B RT_SCOPE_UNIVERSE
 272 and
 273 .B RT_SCOPE_SITE
 274 are available to the user.
 275 .IP
 276 The
 277 .I rtm_flags
 278 have the following meanings:
 279 .TS
 280 tab(:);
 281 lb l.
 282 RTM_F_NOTIFY:T{
 283 if the route changes, notify the user via rtnetlink
 284 T}
 285 RTM_F_CLONED:route is cloned from another route
 286 RTM_F_EQUALIZE:a multipath equalizer (not yet implemented)
 287 .TE
 288 .sp 1
 289 .I rtm_table
 290 specifies the routing table
 291 .TS
 292 tab(:);
 293 lb l.
 294 RT_TABLE_UNSPEC:an unspecified routing table
 295 RT_TABLE_DEFAULT:the default table
 296 RT_TABLE_MAIN:the main table
 297 RT_TABLE_LOCAL:the local table
 298 .TE
 299 .sp 1
 300 The user may assign arbitrary values between
 301 .B RT_TABLE_UNSPEC
 302 and
 303 .BR RT_TABLE_DEFAULT .
 304 .\" Keep table on same page
 305 .bp +1
 306 .TS
 307 tab(:);
 308 c s s
 309 lb2 l2 l.
 310 Attributes
 311 rta_type:Value type:Description
 312 _
 313 RTA_UNSPEC:-:ignored
 314 RTA_DST:protocol address:Route destination address
 315 RTA_SRC:protocol address:Route source address
 316 RTA_IIF:int:Input interface index
 317 RTA_OIF:int:Output interface index
 318 RTA_GATEWAY:protocol address:The gateway of the route
 319 RTA_PRIORITY:int:Priority of route
 320 RTA_PREFSRC:protocol address:Preferred source address
 321 RTA_METRICS:int:Route metric
 322 RTA_MULTIPATH::T{
 323 Multipath nexthop data
 324 br
 325 (see below).
 326 T}
 327 RTA_PROTOINFO::No longer used
 328 RTA_FLOW:int:Route realm
 329 RTA_CACHEINFO:struct rta_cacheinfo:(see linux/rtnetlink.h)
 330 RTA_SESSION::No longer used
 331 RTA_MP_ALGO::No longer used
 332 RTA_TABLE:int:T{
 333 Routing table ID; if set,
 334 .br
 335 rtm_table is ignored
 336 T}
 337 RTA_MARK:int:
 338 RTA_MFC_STATS:struct rta_mfc_stats:(see linux/rtnetlink.h)
 339 RTA_VIA:struct rtvia:T{
 340 Gateway in different AF
 341 (see below)
 342 T}
 343 RTA_NEWDST:protocol address:T{
 344 Change packet
 345 destination address
 346 T}
 347 RTA_PREF:char:T{
 348 RFC4191 IPv6 router
 349 preference (see below)
 350 T}
 351 RTA_ENCAP_TYPE:short:T{
 352 Encapsulation type for
 353 .br
 354 lwtunnels (see below)
 355 T}
 356 RTA_ENCAP::Defined by RTA_ENCAP_TYPE
 357 RTA_EXPIRES:int:T{
 358 Expire time for IPv6
 359 routes (in seconds)
 360 T}
 361 .TE
 362 .IP
 363 .B RTA_MULTIPATH
 364 contains several packed instances of
 365 .I struct rtnexthop
 366 together with nested RTAs
 367 .RB ( RTA_GATEWAY ):
 368 .IP
 369 .in +4n
 370 .EX
 371 struct rtnexthop {
 372     unsigned short rtnh_len;     /* Length of struct + length
 373                                     of RTAs */
 374     unsigned char  rtnh_flags;   /* Flags (see
 375                                     linux/rtnetlink.h) */
 376     unsigned char  rtnh_hops;    /* Nexthop priority */
 377     int            rtnh_ifindex; /* Interface index for this
 378                                     nexthop */
 379 }
 380 .EE
 381 .in
 382 .IP
 383 There exist a bunch of
 384 .B RTNH_*
 385 macros similar to
 386 .B RTA_*
 387 and
 388 .B NLHDR_*
 389 macros
 390 useful to handle these structures.
 391 .IP
 392 .in +4n
 393 .EX
 394 struct rtvia {
 395     unsigned short rtvia_family;
 396     unsigned char  rtvia_addr[0];
 397 };
 398 .EE
 399 .in
 400 .IP
 401 .I rtvia_addr
 402 is the address,
 403 .I rtvia_family
 404 is its family type.
 405 .IP
 406 .B RTA_PREF
 407 may contain values
 408 .BR ICMPV6_ROUTER_PREF_LOW ,
 409 .BR ICMPV6_ROUTER_PREF_MEDIUM ,
 410 and
 411 .BR ICMPV6_ROUTER_PREF_HIGH
 412 defined incw
 413 .IR <linux/icmpv6.h> .
 414 .IP
 415 .B RTA_ENCAP_TYPE
 416 may contain values
 417 .BR LWTUNNEL_ENCAP_MPLS ,
 418 .BR LWTUNNEL_ENCAP_IP ,
 419 .BR LWTUNNEL_ENCAP_ILA ,
 420 or
 421 .BR LWTUNNEL_ENCAP_IP6
 422 defined in
 423 .IR <linux/lwtunnel.h> .
 424 .IP
 425 .B Fill these values in!
 426 .TP
 427 .BR RTM_NEWNEIGH ", " RTM_DELNEIGH  ", " RTM_GETNEIGH
 428 Add, remove, or receive information about a neighbor table
 429 entry (e.g., an ARP entry).
 430 The message contains an
 431 .I ndmsg
 432 structure.
 433 .IP
 434 .EX
 435 struct ndmsg {
 436     unsigned char ndm_family;
 437     int           ndm_ifindex;  /* Interface index */
 438     __u16         ndm_state;    /* State */
 439     __u8          ndm_flags;    /* Flags */
 440     __u8          ndm_type;
 441 };
 442
 443 struct nda_cacheinfo {
 444     __u32         ndm_confirmed;
 445     __u32         ndm_used;
 446     __u32         ndm_updated;
 447     __u32         ndm_refcnt;
 448 };
 449 .EE
 450 .IP
 451 .I ndm_state
 452 is a bit mask of the following states:
 453 .TS
 454 tab(:);
 455 lb l.
 456 NUD_INCOMPLETE:a currently resolving cache entry
 457 NUD_REACHABLE:a confirmed working cache entry
 458 NUD_STALE:an expired cache entry
 459 NUD_DELAY:an entry waiting for a timer
 460 NUD_PROBE:a cache entry that is currently reprobed
 461 NUD_FAILED:an invalid cache entry
 462 NUD_NOARP:a device with no destination cache
 463 NUD_PERMANENT:a static entry
 464 .TE
 465 .sp 1
 466 Valid
 467 .I ndm_flags
 468 are:
 469 .TS
 470 tab(:);
 471 lb l.
 472 NTF_PROXY:a proxy arp entry
 473 NTF_ROUTER:an IPv6 router
 474 .TE
 475 .sp 1
 476 .\" FIXME .
 477 .\" document the members of the struct better
 478 The
 479 .I rtattr
 480 struct has the following meanings for the
 481 .I rta_type
 482 field:
 483 .TS
 484 tab(:);
 485 lb l.
 486 NDA_UNSPEC:unknown type
 487 NDA_DST:a neighbor cache n/w layer destination address
 488 NDA_LLADDR:a neighbor cache link layer address
 489 NDA_CACHEINFO:cache statistics
 490 .TE
 491 .sp 1
 492 If the
 493 .I rta_type
 494 field is
 495 .BR NDA_CACHEINFO ,
 496 then a
 497 .I struct nda_cacheinfo
 498 header follows.
 499 .TP
 500 .BR RTM_NEWRULE ", " RTM_DELRULE ", " RTM_GETRULE
 501 Add, delete, or retrieve a routing rule.
 502 Carries a
 503 .I struct rtmsg
 504 .TP
 505 .BR RTM_NEWQDISC ", " RTM_DELQDISC ", " RTM_GETQDISC
 506 Add, remove, or get a queueing discipline.
 507 The message contains a
 508 .I struct tcmsg
 509 and may be followed by a series of
 510 attributes.
 511 .IP
 512 .EX
 513 struct tcmsg {
 514     unsigned char    tcm_family;
 515     int              tcm_ifindex;   /* interface index */
 516     __u32            tcm_handle;    /* Qdisc handle */
 517     __u32            tcm_parent;    /* Parent qdisc */
 518     __u32            tcm_info;
 519 };
 520 .EE
 521 .TS
 522 tab(:);
 523 c s s
 524 lb2 l2 l.
 525 Attributes
 526 rta_type:Value type:Description
 527 _
 528 TCA_UNSPEC:-:unspecified
 529 TCA_KIND:asciiz string:Name of queueing discipline
 530 TCA_OPTIONS:byte sequence:Qdisc-specific options follow
 531 TCA_STATS:struct tc_stats:Qdisc statistics
 532 TCA_XSTATS:qdisc-specific:Module-specific statistics
 533 TCA_RATE:struct tc_estimator:Rate limit
 534 .TE
 535 .sp 1
 536 In addition, various other qdisc-module-specific attributes are allowed.
 537 For more information see the appropriate include files.
 538 .TP
 539 .BR RTM_NEWTCLASS ", " RTM_DELTCLASS ", " RTM_GETTCLASS
 540 Add, remove, or get a traffic class.
 541 These messages contain a
 542 .I struct tcmsg
 543 as described above.
 544 .TP
 545 .BR RTM_NEWTFILTER ", " RTM_DELTFILTER ", " RTM_GETTFILTER
 546 Add, remove, or receive information about a traffic filter.
 547 These messages contain a
 548 .I struct tcmsg
 549 as described above.
 550 .SH VERSIONS
 551 .B rtnetlink
 552 is a new feature of Linux 2.2.
 553 .SH BUGS
 554 This manual page is incomplete.
 555 .SH SEE ALSO
 556 .BR cmsg (3),
 557 .BR rtnetlink (3),
 558 .BR ip (7),
 559 .BR netlink (7)