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     unsigned char rtm_table;    /* Routing table ID;
 203                                    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 l2 l2 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::T{
 325 Multipath nexthop data
 326 br
 327 (see below).
 328 T}
 329 RTA_PROTOINFO::No longer used
 330 RTA_FLOW:int:Route realm
 331 RTA_CACHEINFO:struct rta_cacheinfo:(see linux/rtnetlink.h)
 332 RTA_SESSION::No longer used
 333 RTA_MP_ALGO::No longer used
 334 RTA_TABLE:int:T{
 335 Routing table ID; if set,
 336 .br
 337 rtm_table is ignored
 338 T}
 339 RTA_MARK:int:
 340 RTA_MFC_STATS:struct rta_mfc_stats:(see linux/rtnetlink.h)
 341 RTA_VIA:struct rtvia:T{
 342 Gateway in different AF
 343 (see below)
 344 T}
 345 RTA_NEWDST:protocol address:T{
 346 Change packet
 347 destination address
 348 T}
 349 RTA_PREF:char:T{
 350 RFC4191 IPv6 router
 351 preference (see below)
 352 T}
 353 RTA_ENCAP_TYPE:short:T{
 354 Encapsulation type for
 355 .br
 356 lwtunnels (see below)
 357 T}
 358 RTA_ENCAP::Defined by RTA_ENCAP_TYPE
 359 RTA_EXPIRES:int:T{
 360 Expire time for IPv6
 361 routes (in seconds)
 362 T}
 363 .TE
 364 .PP
 365 .I RTA_MULTIPATH
 366 contains several packed instances of
 367 .I struct rtnexthop
 368 together with nested RTAs
 369 .RB ( RTA_GATEWAY ):
 370 .PP
 371 .in +4n
 372 .EX
 373 struct rtnexthop {
 374     unsigned short rtnh_len;     /* Length of struct + length
 375                                     of RTAs */
 376     unsigned char  rtnh_flags;   /* Flags (see linux/rtnetlink.h) */
 377     unsigned char  rtnh_hops;    /* Nexthop priority */
 378     int            rtnh_ifindex; /* Interface index for this
 379                                     nexthop */
 380 }
 381 .EE
 382 .in
 383 .PP
 384 There exist a bunch of RTNH_* macros similar to RTA_* and NLHDR_* macros
 385 useful to handle these structures.
 386 .PP
 387 .nf
 388 .in +4n
 389 .EX
 390 struct rtvia {
 391     unsigned short rtvia_family;
 392     unsigned char  rtvia_addr[0];
 393 };
 394 .EE
 395 .in
 396 .PP
 397 .I rtvia_addr
 398 is the address,
 399 .I rtvia_family
 400 is its family type.
 401 .PP
 402 .I RTA_PREF
 403 may contain values ICMPV6_ROUTER_PREF_LOW,
 404 ICMPV6_ROUTER_PREF_MEDIUM and
 405 ICMPV6_ROUTER_PREF_HIGH defined in <linux/icmpv6.h>
 406 .PP
 407 .I RTA_ENCAP_TYPE
 408 may contain values
 409 LWTUNNEL_ENCAP_MPLS, LWTUNNEL_ENCAP_IP,
 410 LWTUNNEL_ENCAP_ILA or LWTUNNEL_ENCAP_IP6
 411 defined in <linux/lwtunnel.h>.
 412 .sp 1
 413 .B Fill these values in!
 414 .TP
 415 .BR RTM_NEWNEIGH ", " RTM_DELNEIGH  ", " RTM_GETNEIGH
 416 Add, remove or receive information about a neighbor table
 417 entry (e.g., an ARP entry).
 418 The message contains an
 419 .I ndmsg
 420 structure.
 421 .IP
 422 .EX
 423 struct ndmsg {
 424     unsigned char ndm_family;
 425     int           ndm_ifindex;  /* Interface index */
 426     __u16         ndm_state;    /* State */
 427     __u8          ndm_flags;    /* Flags */
 428     __u8          ndm_type;
 429 };
 430
 431 struct nda_cacheinfo {
 432     __u32         ndm_confirmed;
 433     __u32         ndm_used;
 434     __u32         ndm_updated;
 435     __u32         ndm_refcnt;
 436 };
 437 .EE
 438 .IP
 439 .I ndm_state
 440 is a bit mask of the following states:
 441 .TS
 442 tab(:);
 443 l l.
 444 NUD_INCOMPLETE:a currently resolving cache entry
 445 NUD_REACHABLE:a confirmed working cache entry
 446 NUD_STALE:an expired cache entry
 447 NUD_DELAY:an entry waiting for a timer
 448 NUD_PROBE:a cache entry that is currently reprobed
 449 NUD_FAILED:an invalid cache entry
 450 NUD_NOARP:a device with no destination cache
 451 NUD_PERMANENT:a static entry
 452 .TE
 453 .sp 1
 454 Valid
 455 .I ndm_flags
 456 are:
 457 .TS
 458 tab(:);
 459 l l.
 460 NTF_PROXY:a proxy arp entry
 461 NTF_ROUTER:an IPv6 router
 462 .TE
 463 .sp 1
 464 .\" FIXME .
 465 .\" document the members of the struct better
 466 The
 467 .I rtattr
 468 struct has the following meanings for the
 469 .I rta_type
 470 field:
 471 .TS
 472 tab(:);
 473 l l.
 474 NDA_UNSPEC:unknown type
 475 NDA_DST:a neighbor cache n/w layer destination address
 476 NDA_LLADDR:a neighbor cache link layer address
 477 NDA_CACHEINFO:cache statistics
 478 .TE
 479 .sp 1
 480 If the
 481 .I rta_type
 482 field is
 483 .BR NDA_CACHEINFO ,
 484 then a
 485 .I struct nda_cacheinfo
 486 header follows
 487 .TP
 488 .BR RTM_NEWRULE ", " RTM_DELRULE ", " RTM_GETRULE
 489 Add, delete or retrieve a routing rule.
 490 Carries a
 491 .I struct rtmsg
 492 .TP
 493 .BR RTM_NEWQDISC ", " RTM_DELQDISC ", " RTM_GETQDISC
 494 Add, remove or get a queueing discipline.
 495 The message contains a
 496 .I struct tcmsg
 497 and may be followed by a series of
 498 attributes.
 499 .IP
 500 .EX
 501 struct tcmsg {
 502     unsigned char    tcm_family;
 503     int              tcm_ifindex;   /* interface index */
 504     __u32            tcm_handle;    /* Qdisc handle */
 505     __u32            tcm_parent;    /* Parent qdisc */
 506     __u32            tcm_info;
 507 };
 508 .EE
 509 .TS
 510 tab(:);
 511 c s s
 512 l2 l2 l.
 513 Attributes
 514 rta_type:Value type:Description
 515 _
 516 TCA_UNSPEC:-:unspecified
 517 TCA_KIND:asciiz string:Name of queueing discipline
 518 TCA_OPTIONS:byte sequence:Qdisc-specific options follow
 519 TCA_STATS:struct tc_stats:Qdisc statistics
 520 TCA_XSTATS:qdisc-specific:Module-specific statistics
 521 TCA_RATE:struct tc_estimator:Rate limit
 522 .TE
 523 .sp 1
 524 In addition, various other qdisc-module-specific attributes are allowed.
 525 For more information see the appropriate include files.
 526 .TP
 527 .BR RTM_NEWTCLASS ", " RTM_DELTCLASS ", " RTM_GETTCLASS
 528 Add, remove or get a traffic class.
 529 These messages contain a
 530 .I struct tcmsg
 531 as described above.
 532 .TP
 533 .BR RTM_NEWTFILTER ", " RTM_DELTFILTER ", " RTM_GETTFILTER
 534 Add, remove or receive information about a traffic filter.
 535 These messages contain a
 536 .I struct tcmsg
 537 as described above.
 538 .SH VERSIONS
 539 .B rtnetlink
 540 is a new feature of Linux 2.2.
 541 .SH BUGS
 542 This manual page is incomplete.
 543 .SH SEE ALSO
 544 .BR cmsg (3),
 545 .BR rtnetlink (3),
 546 .BR ip (7),
 547 .BR netlink (7)