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/socket.h> 43.Fd #include <net/if.h> 44.Fd #include <net/route.h> 45.Ft int 46.Fn socket PF_ROUTE SOCK_RAW "int family" 47.Sh DESCRIPTION 48.Tn UNIX 49provides some packet routing facilities. 50The kernel maintains a routing information database, which 51is used in selecting the appropriate network interface when 52transmitting packets. 53.Pp 54A user process (or possibly multiple co-operating processes) 55maintains this database by sending messages over a special kind 56of socket. 57This supplants fixed size 58.Xr ioctl 2 Ns 's 59used in earlier releases. 60Routing table changes may only be carried out by the super user. 61.Pp 62The operating system may spontaneously emit routing messages in response 63to external events, such as receipt of a re-direct, or failure to 64locate a suitable route for a request. 65The message types are described in greater detail below. 66.Pp 67Routing database entries come in two flavors: for a specific 68host, or for all hosts on a generic subnetwork (as specified 69by a bit mask and value under the mask. 70The effect of wildcard or default route may be achieved by using 71a mask of all zeros, and there may be hierarchical routes. 72.Pp 73When the system is booted and addresses are assigned 74to the network interfaces, each protocol family 75installs a routing table entry for each interface when it is ready for traffic. 76Normally the protocol specifies the route 77through each interface as a 78.Dq direct 79connection to the destination host 80or network. If the route is direct, the transport layer of 81a protocol family usually requests the packet be sent to the 82same host specified in the packet. Otherwise, the interface 83is requested to address the packet to the gateway listed in the routing entry 84(i.e. the packet is forwarded). 85.Pp 86When routing a packet, 87the kernel will attempt to find 88the most specific route matching the destination. 89(If there are two different mask and value-under-the-mask pairs 90that match, the more specific is the one with more bits in the mask. 91A route to a host is regarded as being supplied with a mask of 92as many ones as there are bits in the destination). 93If no entry is found, the destination is declared to be unreachable, 94and a routing\-miss message is generated if there are any 95listers on the routing control socket described below. 96.Pp 97A wildcard routing entry is specified with a zero 98destination address value, and a mask of all zeroes. 99Wildcard routes will be used 100when the system fails to find other routes matching the 101destination. The combination of wildcard 102routes and routing redirects can provide an economical 103mechanism for routing traffic. 104.Pp 105One opens the channel for passing routing control messages 106by using the socket call shown in the synopsis above: 107.Pp 108The 109.Fa family 110parameter may be 111.Dv AF_UNSPEC 112which will provide 113routing information for all address families, or can be restricted 114to a specific address family by specifying which one is desired. 115There can be more than one routing socket open per system. 116.Pp 117Messages are formed by a header followed by a small 118number of sockadders (now variable length particularly 119in the 120.Tn ISO 121case), interpreted by position, and delimited 122by the new length entry in the sockaddr. 123An example of a message with four addresses might be an 124.Tn ISO 125redirect: 126Destination, Netmask, Gateway, and Author of the redirect. 127The interpretation of which address are present is given by a 128bit mask within the header, and the sequence is least significant 129to most significant bit within the vector. 130.Pp 131Any messages sent to the kernel are returned, and copies are sent 132to all interested listeners. The kernel will provide the process 133id. for the sender, and the sender may use an additional sequence 134field to distinguish between outstanding messages. However, 135message replies may be lost when kernel buffers are exhausted. 136.Pp 137The kernel may reject certain messages, and will indicate this 138by filling in the 139.Ar rtm_errno 140field. 141The routing code returns 142.Dv EEXIST 143if 144requested to duplicate an existing entry, 145.Dv ESRCH 146if 147requested to delete a non-existent entry, 148or 149.Dv ENOBUFS 150if insufficient resources were available 151to install a new route. 152In the current implementation, all routing process run locally, 153and the values for 154.Ar rtm_errno 155are available through the normal 156.Em errno 157mechanism, even if the routing reply message is lost. 158.Pp 159A process may avoid the expense of reading replies to 160its own messages by issuing a 161.Xr setsockopt 2 162call indicating that the 163.Dv SO_USELOOPBACK 164option 165at the 166.Dv SOL_SOCKET 167level is to be turned off. 168A process may ignore all messages from the routing socket 169by doing a 170.Xr shutdown 2 171system call for further input. 172.Pp 173If a route is in use when it is deleted, 174the routing entry will be marked down and removed from the routing table, 175but the resources associated with it will not 176be reclaimed until all references to it are released. 177User processes can obtain information about the routing 178entry to a specific destination by using a 179.Dv RTM_GET 180message, 181or by reading the 182.Pa /dev/kmem 183device, or by issuing a 184.Xr getkerninfo 2 185system call. 186.Pp 187Messages include: 188.Bd -literal 189#define RTM_ADD 0x1 /* Add Route */ 190#define RTM_DELETE 0x2 /* Delete Route */ 191#define RTM_CHANGE 0x3 /* Change Metrics, Flags, or Gateway */ 192#define RTM_GET 0x4 /* Report Information */ 193#define RTM_LOOSING 0x5 /* Kernel Suspects Partitioning */ 194#define RTM_REDIRECT 0x6 /* Told to use different route */ 195#define RTM_MISS 0x7 /* Lookup failed on this address */ 196#define RTM_RESOLVE 0xb /* request to resolve dst to LL addr */ 197.Ed 198.Pp 199A message header consists of: 200.Bd -literal 201struct rt_msghdr { 202 u_short rmt_msglen; /* to skip over non-understood messages */ 203 u_char rtm_version; /* future binary compatibility */ 204 u_char rtm_type; /* message type */ 205 u_short rmt_index; /* index for associated ifp */ 206 int rtm_flags; /* flags, incl kern & message, e.g. DONE */ 207 int rtm_addrs; /* bitmask identifying sockaddrs in msg */ 208 pid_t rmt_pid; /* identify sender */ 209 int rtm_seq; /* for sender to identify action */ 210 int rtm_errno; /* why failed */ 211 int rtm_use; /* from rtentry */ 212 u_long rtm_inits; /* which values we are initializing */ 213 struct rt_metrics rtm_rmx; /* metrics themselves */ 214}; 215.Ed 216.Pp 217where 218.Dq Li "struct rt_metrics" 219and the flag bits are as defined in 220.Xr rtentry 9 . 221.Pp 222Specifiers for metric values in rmx_locks and rtm_inits are: 223.Bd -literal 224#define RTV_SSTHRESH 0x1 /* init or lock _ssthresh */ 225#define RTV_RPIPE 0x2 /* init or lock _recvpipe */ 226#define RTV_SPIPE 0x4 /* init or lock _sendpipe */ 227#define RTV_HOPCOUNT 0x8 /* init or lock _hopcount */ 228#define RTV_RTT 0x10 /* init or lock _rtt */ 229#define RTV_RTTVAR 0x20 /* init or lock _rttvar */ 230#define RTV_MTU 0x40 /* init or lock _mtu */ 231.Ed 232.Pp 233Specifiers for which addresses are present in the messages are: 234.Bd -literal 235#define RTA_DST 0x1 /* destination sockaddr present */ 236#define RTA_GATEWAY 0x2 /* gateway sockaddr present */ 237#define RTA_NETMASK 0x4 /* netmask sockaddr present */ 238#define RTA_GENMASK 0x8 /* cloning mask sockaddr present */ 239#define RTA_IFP 0x10 /* interface name sockaddr present */ 240#define RTA_IFA 0x20 /* interface addr sockaddr present */ 241#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */ 242.Ed 243.Sh SEE ALSO 244.Xr route 8 , 245.Xr rtentry 9 246.Sh HISTORY 247A 248.Dv PF_ROUTE 249protocol family first appeared in 250.Bx 4.3 reno . 251