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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)route.4 8.6 (Berkeley) 4/19/94 33.\" $FreeBSD$ 34.\" 35.Dd October 8, 1996 36.Dt ROUTE 4 37.Os 38.Sh NAME 39.Nm route 40.Nd kernel packet forwarding database 41.Sh SYNOPSIS 42.Fd #include <sys/types.h> 43.Fd #include <sys/time.h> 44.Fd #include <sys/socket.h> 45.Fd #include <net/if.h> 46.Fd #include <net/route.h> 47.Ft int 48.Fn socket PF_ROUTE SOCK_RAW "int family" 49.Sh DESCRIPTION 50.Fx 51provides some packet routing facilities. 52The kernel maintains a routing information database, which 53is used in selecting the appropriate network interface when 54transmitting packets. 55.Pp 56A user process (or possibly multiple co-operating processes) 57maintains this database by sending messages over a special kind 58of socket. 59This supplants fixed size 60.Xr ioctl 2 Ns 's 61used in earlier releases. 62Routing table changes may only be carried out by the super user. 63.Pp 64The operating system may spontaneously emit routing messages in response 65to external events, such as receipt of a re-direct, or failure to 66locate a suitable route for a request. 67The message types are described in greater detail below. 68.Pp 69Routing database entries come in two flavors: for a specific 70host, or for all hosts on a generic subnetwork (as specified 71by a bit mask and value under the mask. 72The effect of wildcard or default route may be achieved by using 73a mask of all zeros, and there may be hierarchical routes. 74.Pp 75When the system is booted and addresses are assigned 76to the network interfaces, each protocol family 77installs a routing table entry for each interface when it is ready for traffic. 78Normally the protocol specifies the route 79through each interface as a 80.Dq direct 81connection to the destination host 82or network. If the route is direct, the transport layer of 83a protocol family usually requests the packet be sent to the 84same host specified in the packet. Otherwise, the interface 85is requested to address the packet to the gateway listed in the routing entry 86(i.e. the packet is forwarded). 87.Pp 88When routing a packet, 89the kernel will attempt to find 90the most specific route matching the destination. 91(If there are two different mask and value-under-the-mask pairs 92that match, the more specific is the one with more bits in the mask. 93A route to a host is regarded as being supplied with a mask of 94as many ones as there are bits in the destination). 95If no entry is found, the destination is declared to be unreachable, 96and a routing\-miss message is generated if there are any 97listers on the routing control socket described below. 98.Pp 99A wildcard routing entry is specified with a zero 100destination address value, and a mask of all zeroes. 101Wildcard routes will be used 102when the system fails to find other routes matching the 103destination. The combination of wildcard 104routes and routing redirects can provide an economical 105mechanism for routing traffic. 106.Pp 107One opens the channel for passing routing control messages 108by using the socket call shown in the synopsis above: 109.Pp 110The 111.Fa family 112parameter may be 113.Dv AF_UNSPEC 114which will provide 115routing information for all address families, or can be restricted 116to a specific address family by specifying which one is desired. 117There can be more than one routing socket open per system. 118.Pp 119Messages are formed by a header followed by a small 120number of sockaddrs (now variable length particularly 121in the 122.Tn ISO 123case), interpreted by position, and delimited 124by the new length entry in the sockaddr. 125An example of a message with four addresses might be an 126.Tn ISO 127redirect: 128Destination, Netmask, Gateway, and Author of the redirect. 129The interpretation of which address are present is given by a 130bit mask within the header, and the sequence is least significant 131to most significant bit within the vector. 132.Pp 133Any messages sent to the kernel are returned, and copies are sent 134to all interested listeners. The kernel will provide the process 135ID for the sender, and the sender may use an additional sequence 136field to distinguish between outstanding messages. However, 137message replies may be lost when kernel buffers are exhausted. 138.Pp 139The kernel may reject certain messages, and will indicate this 140by filling in the 141.Ar rtm_errno 142field. 143The routing code returns 144.Er EEXIST 145if 146requested to duplicate an existing entry, 147.Er ESRCH 148if 149requested to delete a non-existent entry, 150or 151.Er ENOBUFS 152if insufficient resources were available 153to install a new route. 154In the current implementation, all routing processes run locally, 155and the values for 156.Ar rtm_errno 157are available through the normal 158.Em errno 159mechanism, even if the routing reply message is lost. 160.Pp 161A process may avoid the expense of reading replies to 162its own messages by issuing a 163.Xr setsockopt 2 164call indicating that the 165.Dv SO_USELOOPBACK 166option 167at the 168.Dv SOL_SOCKET 169level is to be turned off. 170A process may ignore all messages from the routing socket 171by doing a 172.Xr shutdown 2 173system call for further input. 174.Pp 175If a route is in use when it is deleted, 176the routing entry will be marked down and removed from the routing table, 177but the resources associated with it will not 178be reclaimed until all references to it are released. 179User processes can obtain information about the routing 180entry to a specific destination by using a 181.Dv RTM_GET 182message, or by calling 183.Xr sysctl 3 . 184.Pp 185Messages include: 186.Bd -literal 187#define RTM_ADD 0x1 /* Add Route */ 188#define RTM_DELETE 0x2 /* Delete Route */ 189#define RTM_CHANGE 0x3 /* Change Metrics, Flags, or Gateway */ 190#define RTM_GET 0x4 /* Report Information */ 191#define RTM_LOSING 0x5 /* Kernel Suspects Partitioning */ 192#define RTM_REDIRECT 0x6 /* Told to use different route */ 193#define RTM_MISS 0x7 /* Lookup failed on this address */ 194#define RTM_LOCK 0x8 /* fix specified metrics */ 195#define RTM_RESOLVE 0xb /* request to resolve dst to LL addr */ 196#define RTM_NEWADDR 0xc /* address being added to iface */ 197#define RTM_DELADDR 0xd /* address being removed from iface */ 198#define RTM_IFINFO 0xe /* iface going up/down etc. */ 199#define RTM_NEWMADDR 0xf /* mcast group membership being added to if */ 200#define RTM_DELMADDR 0x10 /* mcast group membership being deleted */ 201.Ed 202.Pp 203A message header consists of one of the following: 204.Bd -literal 205struct rt_msghdr { 206 u_short rtm_msglen; /* to skip over non-understood messages */ 207 u_char rtm_version; /* future binary compatibility */ 208 u_char rtm_type; /* message type */ 209 u_short rtm_index; /* index for associated ifp */ 210 int rtm_flags; /* flags, incl. kern & message, e.g. DONE */ 211 int rtm_addrs; /* bitmask identifying sockaddrs in msg */ 212 pid_t rtm_pid; /* identify sender */ 213 int rtm_seq; /* for sender to identify action */ 214 int rtm_errno; /* why failed */ 215 int rtm_use; /* from rtentry */ 216 u_long rtm_inits; /* which metrics we are initializing */ 217 struct rt_metrics rtm_rmx; /* metrics themselves */ 218}; 219 220struct if_msghdr { 221 u_short ifm_msglen; /* to skip over non-understood messages */ 222 u_char ifm_version; /* future binary compatibility */ 223 u_char ifm_type; /* message type */ 224 int ifm_addrs; /* like rtm_addrs */ 225 int ifm_flags; /* value of if_flags */ 226 u_short ifm_index; /* index for associated ifp */ 227 struct if_data ifm_data; /* statistics and other data about if */ 228}; 229 230struct ifa_msghdr { 231 u_short ifam_msglen; /* to skip over non-understood messages */ 232 u_char ifam_version; /* future binary compatibility */ 233 u_char ifam_type; /* message type */ 234 int ifam_addrs; /* like rtm_addrs */ 235 int ifam_flags; /* value of ifa_flags */ 236 u_short ifam_index; /* index for associated ifp */ 237 int ifam_metric; /* value of ifa_metric */ 238}; 239 240struct ifma_msghdr { 241 u_short ifmam_msglen; /* to skip over non-understood messages */ 242 u_char ifmam_version; /* future binary compatibility */ 243 u_char ifmam_type; /* message type */ 244 int ifmam_addrs; /* like rtm_addrs */ 245 int ifmam_flags; /* value of ifa_flags */ 246 u_short ifmam_index; /* index for associated ifp */ 247}; 248.Ed 249.Pp 250The 251.Dv RTM_IFINFO 252message uses a 253.Ar if_msghdr 254header, the 255.Dv RTM_NEWADDR 256and 257.Dv RTM_DELADDR 258messages use a 259.Ar ifa_msghdr 260header, the 261.Dv RTM_NEWMADDR 262and 263.Dv RTM_DELMADDR 264messages use a 265.Ar ifma_msghdr , 266and all other messages use the 267.Ar rt_msghdr 268header. 269.Pp 270The 271.Dq Li "struct rt_metrics" 272and the flag bits are as defined in 273.Xr rtentry 9 . 274.Pp 275Specifiers for metric values in rmx_locks and rtm_inits are: 276.Bd -literal 277#define RTV_MTU 0x1 /* init or lock _mtu */ 278#define RTV_HOPCOUNT 0x2 /* init or lock _hopcount */ 279#define RTV_EXPIRE 0x4 /* init or lock _expire */ 280#define RTV_RPIPE 0x8 /* init or lock _recvpipe */ 281#define RTV_SPIPE 0x10 /* init or lock _sendpipe */ 282#define RTV_SSTHRESH 0x20 /* init or lock _ssthresh */ 283#define RTV_RTT 0x40 /* init or lock _rtt */ 284#define RTV_RTTVAR 0x80 /* init or lock _rttvar */ 285.Ed 286.Pp 287Specifiers for which addresses are present in the messages are: 288.Bd -literal 289#define RTA_DST 0x1 /* destination sockaddr present */ 290#define RTA_GATEWAY 0x2 /* gateway sockaddr present */ 291#define RTA_NETMASK 0x4 /* netmask sockaddr present */ 292#define RTA_GENMASK 0x8 /* cloning mask sockaddr present */ 293#define RTA_IFP 0x10 /* interface name sockaddr present */ 294#define RTA_IFA 0x20 /* interface addr sockaddr present */ 295#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */ 296#define RTA_BRD 0x80 /* for NEWADDR, broadcast or p-p dest addr */ 297.Ed 298.Sh SEE ALSO 299.Xr sysctl 3 , 300.Xr route 8 , 301.Xr rtentry 9 302.Sh HISTORY 303A 304.Dv PF_ROUTE 305protocol family first appeared in 306.Bx 4.3 reno . 307