1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" From: @(#)route.4 8.6 (Berkeley) 4/19/94 29.\" $FreeBSD: src/share/man/man4/route.4,v 1.9.2.6 2002/03/17 09:12:44 schweikh Exp $ 30.\" $DragonFly: src/share/man/man4/route.4,v 1.3 2004/03/11 12:28:55 hmp Exp $ 31.\" 32.Dd August 7, 2019 33.Dt ROUTE 4 34.Os 35.Sh NAME 36.Nm route 37.Nd kernel packet forwarding database 38.Sh SYNOPSIS 39.In sys/types.h 40.In sys/time.h 41.In sys/socket.h 42.In net/if.h 43.In net/route.h 44.Ft int 45.Fn socket PF_ROUTE SOCK_RAW "int family" 46.Sh DESCRIPTION 47.Dx 48provides some packet routing facilities. 49The kernel maintains a routing information database, which 50is used in selecting the appropriate network interface when 51transmitting packets. 52.Pp 53A user process (or possibly multiple co-operating processes) 54maintains this database by sending messages over a special kind 55of socket. 56This supplants fixed size 57.Xr ioctl 2 Ns 's 58used in earlier releases. 59Routing table changes may only be carried out by the super user. 60.Pp 61The operating system may spontaneously emit routing messages in response 62to external events, such as receipt of a re-direct, or failure to 63locate a suitable route for a request. 64The message types are described in greater detail below. 65.Pp 66Routing database entries come in two flavors: for a specific 67host, or for all hosts on a generic subnetwork (as specified 68by a bit mask and value under the mask. 69The effect of wildcard or default route may be achieved by using 70a mask of all zeros, and there may be hierarchical routes. 71.Pp 72When the system is booted and addresses are assigned 73to the network interfaces, each protocol family 74installs a routing table entry for each interface when it is ready for traffic. 75Normally the protocol specifies the route 76through each interface as a 77.Dq direct 78connection to the destination host 79or network. If the route is direct, the transport layer of 80a protocol family usually requests the packet be sent to the 81same host specified in the packet. Otherwise, the interface 82is requested to address the packet to the gateway listed in the routing entry 83(i.e. the packet is forwarded). 84.Pp 85When routing a packet, 86the kernel will attempt to find 87the most specific route matching the destination. 88(If there are two different mask and value-under-the-mask pairs 89that match, the more specific is the one with more bits in the mask. 90A route to a host is regarded as being supplied with a mask of 91as many ones as there are bits in the destination). 92If no entry is found, the destination is declared to be unreachable, 93and a routing\-miss message is generated if there are any 94listeners on the routing control socket described below. 95.Pp 96A wildcard routing entry is specified with a zero 97destination address value, and a mask of all zeroes. 98Wildcard routes will be used 99when the system fails to find other routes matching the 100destination. The combination of wildcard 101routes and routing redirects can provide an economical 102mechanism for routing traffic. 103.Pp 104One opens the channel for passing routing control messages 105by using the socket call shown in the synopsis above: 106.Pp 107The 108.Fa family 109parameter may be 110.Dv AF_UNSPEC 111which will provide 112routing information for all address families, or can be restricted 113to a specific address family by specifying which one is desired. 114There can be more than one routing socket open per system. 115.Pp 116Messages are formed by a header followed by a small 117number of sockaddrs (now variable length particularly 118in the 119.Tn ISO 120case), interpreted by position, and delimited 121by the new length entry in the sockaddr. 122An example of a message with four addresses might be an 123.Tn ISO 124redirect: 125Destination, Netmask, Gateway, and Author of the redirect. 126The interpretation of which address are present is given by a 127bit mask within the header, and the sequence is least significant 128to most significant bit within the vector. 129.Pp 130Any messages sent to the kernel are returned, and copies are sent 131to all interested listeners. The kernel will provide the process 132ID for the sender, and the sender may use an additional sequence 133field to distinguish between outstanding messages. However, 134message replies may be lost when kernel buffers are exhausted. 135.Pp 136The kernel may reject certain messages, and will indicate this 137by filling in the 138.Ar rtm_errno 139field. 140The routing code returns 141.Er EEXIST 142if 143requested to duplicate an existing entry, 144.Er ESRCH 145if 146requested to delete a non-existent entry, 147or 148.Er ENOBUFS 149if insufficient resources were available 150to install a new route. 151In the current implementation, all routing processes run locally, 152and the values for 153.Ar rtm_errno 154are available through the normal 155.Em errno 156mechanism, even if the routing reply message is lost. 157.Pp 158A process may avoid the expense of reading replies to 159its own messages by issuing a 160.Xr setsockopt 2 161call indicating that the 162.Dv SO_USELOOPBACK 163option 164at the 165.Dv SOL_SOCKET 166level is to be turned off. 167A process may ignore all messages from the routing socket 168by doing a 169.Xr shutdown 2 170system call for further input. 171.Pp 172A process can specify which route message types it's interested in by passing 173an array of route message types to the 174.Xr setsockopt 2 175call with the 176.Dv ROUTE_MSGFILTER 177option at the 178.Dv PF_ROUTE 179level. 180For example, to only get specific messages: 181.Bd -literal -offset indent 182unsigned int rtfilter; 183 184rtfilter = ROUTE_FILTER(RTM_IFINFO) | ROUTE_FILTER(RTM_IFANNOUNCE); 185 186if (setsockopt(routefd, PF_ROUTE, ROUTE_MSGFILTER, 187 &rtfilter, sizeof(rtfilter)) == -1) 188 err(1, "setsockopt(ROUTE_MSGFILTER)"); 189.Ed 190.Pp 191If a route is in use when it is deleted, 192the routing entry will be marked down and removed from the routing table, 193but the resources associated with it will not 194be reclaimed until all references to it are released. 195User processes can obtain information about the routing 196entry to a specific destination by using a 197.Dv RTM_GET 198message, or by calling 199.Xr sysctl 3 . 200.Pp 201Messages include: 202.Bd -literal 203#define RTM_ADD 0x1 /* Add Route */ 204#define RTM_DELETE 0x2 /* Delete Route */ 205#define RTM_CHANGE 0x3 /* Change Metrics, Flags, or Gateway */ 206#define RTM_GET 0x4 /* Report Information */ 207#define RTM_LOSING 0x5 /* Kernel Suspects Partitioning */ 208#define RTM_REDIRECT 0x6 /* Told to use different route */ 209#define RTM_MISS 0x7 /* Lookup failed on this address */ 210#define RTM_LOCK 0x8 /* fix specified metrics */ 211#define RTM_RESOLVE 0xb /* request to resolve dst to LL addr */ 212#define RTM_NEWADDR 0xc /* address being added to iface */ 213#define RTM_DELADDR 0xd /* address being removed from iface */ 214#define RTM_IFINFO 0xe /* iface going up/down etc. */ 215#define RTM_NEWMADDR 0xf /* mcast group membership being added to if */ 216#define RTM_DELMADDR 0x10 /* mcast group membership being deleted */ 217#define RTM_IFANNOUNCE 0x11 /* iface arrival/departure */ 218.Ed 219.Pp 220A message header consists of one of the following: 221.Bd -literal 222struct rt_msghdr { 223 u_short rtm_msglen; /* to skip over non-understood messages */ 224 u_char rtm_version; /* future binary compatibility */ 225 u_char rtm_type; /* message type */ 226 u_short rtm_index; /* index for associated ifp */ 227 int rtm_flags; /* flags, incl. kern & message, e.g. DONE */ 228 int rtm_addrs; /* bitmask identifying sockaddrs in msg */ 229 pid_t rtm_pid; /* identify sender */ 230 int rtm_seq; /* for sender to identify action */ 231 int rtm_errno; /* why failed */ 232 int rtm_use; /* from rtentry */ 233 u_long rtm_inits; /* which metrics we are initializing */ 234 struct rt_metrics rtm_rmx; /* metrics themselves */ 235}; 236 237struct if_msghdr { 238 u_short ifm_msglen; /* to skip over non-understood messages */ 239 u_char ifm_version; /* future binary compatibility */ 240 u_char ifm_type; /* message type */ 241 int ifm_addrs; /* like rtm_addrs */ 242 int ifm_flags; /* value of if_flags */ 243 u_short ifm_index; /* index for associated ifp */ 244 struct if_data ifm_data; /* statistics and other data about if */ 245}; 246 247struct ifa_msghdr { 248 u_short ifam_msglen; /* to skip over non-understood messages */ 249 u_char ifam_version; /* future binary compatibility */ 250 u_char ifam_type; /* message type */ 251 int ifam_addrs; /* like rtm_addrs */ 252 int ifam_flags; /* value of ifa_flags */ 253 u_short ifam_index; /* index for associated ifp */ 254 int ifam_metric; /* value of ifa_metric */ 255}; 256 257struct ifma_msghdr { 258 u_short ifmam_msglen; /* to skip over non-understood messages */ 259 u_char ifmam_version; /* future binary compatibility */ 260 u_char ifmam_type; /* message type */ 261 int ifmam_addrs; /* like rtm_addrs */ 262 int ifmam_flags; /* value of ifa_flags */ 263 u_short ifmam_index; /* index for associated ifp */ 264}; 265 266struct if_announcemsghdr { 267 u_short ifan_msglen; /* to skip over non-understood messages */ 268 u_char ifan_version; /* future binary compatibility */ 269 u_char ifan_type; /* message type */ 270 u_short ifan_index; /* index for associated ifp */ 271 char ifan_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 272 u_short ifan_what; /* what type of announcement */ 273}; 274.Ed 275.Pp 276The 277.Dv RTM_IFINFO 278message uses a 279.Ar if_msghdr 280header, the 281.Dv RTM_NEWADDR 282and 283.Dv RTM_DELADDR 284messages use a 285.Ar ifa_msghdr 286header, the 287.Dv RTM_NEWMADDR 288and 289.Dv RTM_DELMADDR 290messages use a 291.Vt ifma_msghdr 292header, the 293.Dv RTM_IFANNOUNCE 294message uses a 295.Vt if_announcemsghdr 296header, 297and all other messages use the 298.Ar rt_msghdr 299header. 300.Pp 301The 302.Dq Li "struct rt_metrics" 303and the flag bits are as defined in 304.Xr rtentry 9 . 305.Pp 306Specifiers for metric values in rmx_locks and rtm_inits are: 307.Bd -literal 308#define RTV_MTU 0x1 /* init or lock _mtu */ 309#define RTV_HOPCOUNT 0x2 /* init or lock _hopcount */ 310#define RTV_EXPIRE 0x4 /* init or lock _expire */ 311#define RTV_RPIPE 0x8 /* init or lock _recvpipe */ 312#define RTV_SPIPE 0x10 /* init or lock _sendpipe */ 313#define RTV_SSTHRESH 0x20 /* init or lock _ssthresh */ 314#define RTV_RTT 0x40 /* init or lock _rtt */ 315#define RTV_RTTVAR 0x80 /* init or lock _rttvar */ 316.Ed 317.Pp 318Specifiers for which addresses are present in the messages are: 319.Bd -literal 320#define RTA_DST 0x1 /* destination sockaddr present */ 321#define RTA_GATEWAY 0x2 /* gateway sockaddr present */ 322#define RTA_NETMASK 0x4 /* netmask sockaddr present */ 323#define RTA_GENMASK 0x8 /* cloning mask sockaddr present */ 324#define RTA_IFP 0x10 /* interface name sockaddr present */ 325#define RTA_IFA 0x20 /* interface addr sockaddr present */ 326#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */ 327#define RTA_BRD 0x80 /* for NEWADDR, broadcast or p-p dest addr */ 328.Ed 329.Sh SEE ALSO 330.Xr sysctl 3 , 331.Xr route 8 , 332.Xr rtentry 9 333.Sh HISTORY 334A 335.Dv PF_ROUTE 336protocol family first appeared in 337.Bx 4.3 reno . 338