1.\" Copyright (c) 1990, 1991 The Regents of the University of California. 2.\" 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 6.3 (Berkeley) 3/28/91 33.\" $Id: route.4,v 1.2 1993/08/01 07:55:51 mycroft Exp $ 34.\" 35.Dd March 28, 1991 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 recipt 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 first attempt to find a route to the destination host. 88Failing that, a search is made for a route to the network of the destination. 89Finally, any route to a default 90.Pq Dq wildcard 91gateway is chosen. 92If no entry is found, the destination is declared to be unreachable, 93and a routing\-miss message is generated if there are any 94listers on the routing control socket described below. 95.Pp 96A wildcard routing entry is specified with a zero 97destination address value. Wildcard routes are used 98only when the system fails to find a route to the 99destination host and network. The combination of wildcard 100routes and routing redirects can provide an economical 101mechanism for routing traffic. 102.Pp 103One opens the channel for passing routing control messasges 104by using the socket call shown in the synopsis above: 105.Pp 106The 107.Fa family 108paramter may be 109.Dv AF_UNSPEC 110which will provide 111routing information for all address families, or can be restricted 112to a specific address family by specifying which one is desired. 113There can be more than one routing socket open per system. 114.Pp 115Messages are formed by a header followed by a small 116number of sockadders (now variable length particularly 117in the 118.Tn ISO 119case), interpreted by position, and delimited 120by the new length entry in the sockaddr. 121An example of a message with four addresses might be an 122.Tn ISO 123redirect: 124Destination, Netmask, Gateway, and Author of the redirect. 125The interpretation of which address are present is given by a 126bit mask within the header, and the sequence is least significant 127to most significant bit within the vector. 128.Pp 129Any messages sent to the kernel are returned, and copies are sent 130to all interested listeners. The kernel will provide the process 131id. for the sender, and the sender may use an additional sequence 132field to distinguish between outstanding messages. However, 133message replies may be lost when kernel buffers are exhausted. 134.Pp 135The kernel may reject certain messages, and will indicate this 136by filling in the 137.Ar rtm_errno 138field. 139The routing code returns 140.Dv EEXIST 141if 142requested to duplicate an existing entry, 143.Dv ESRCH 144if 145requested to delete a non-existent entry, 146or 147.Dv ENOBUFS 148if insufficient resources were available 149to install a new route. 150In the current implementation, all routing process run locally, 151and the values for 152.Ar rtm_errno 153are available through the normal 154.Em errno 155mechanism, even if the routing reply message is lost. 156.Pp 157A process may avoid the expense of reading replies to 158its own messages by issuing a 159.Xr setsockopt 2 160call indicating that the 161.Dv SO_USELOOPBACK 162option 163at the 164.Dv SOL_SOCKET 165level is to be turned off. 166A process may ignore all messages from the routing socket 167by doing a 168.Xr shutdown 2 169system call for further input. 170.Pp 171If a route is in use when it is deleted, 172the routing entry will be marked down and removed from the routing table, 173but the resources associated with it will not 174be reclaimed until all references to it are released. 175User processes can obtain information about the routing 176entry to a specific destination by using a 177.Dv RTM_GET 178message, 179or by reading the 180.Pa /dev/kmem 181device, or by issuing a 182.Xr getkerninfo 2 183system call. 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_LOOSING 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_RESOLVE 0xb /* request to resolve dst to LL addr */ 195.Ed 196.Pp 197A message header consists of: 198.Bd -literal 199struct rt_msghdr { 200 u_short rmt_msglen; /* to skip over non-understood messages */ 201 u_char rtm_version; /* future binary compatability */ 202 u_char rtm_type; /* message type */ 203 u_short rmt_index; /* index for associated ifp */ 204 pid_t rmt_pid; /* identify sender */ 205 int rtm_addrs; /* bitmask identifying sockaddrs in msg */ 206 int rtm_seq; /* for sender to identify action */ 207 int rtm_errno; /* why failed */ 208 int rtm_flags; /* flags, incl kern & message, e.g. DONE */ 209 int rtm_use; /* from rtentry */ 210 u_long rtm_inits; /* which values we are initializing */ 211 struct rt_metrics rtm_rmx; /* metrics themselves */ 212}; 213.Ed 214.Pp 215where 216.Bd -literal 217struct rt_metrics { 218 u_long rmx_locks; /* Kernel must leave these values alone */ 219 u_long rmx_mtu; /* MTU for this path */ 220 u_long rmx_hopcount; /* max hops expected */ 221 u_long rmx_expire; /* lifetime for route, e.g. redirect */ 222 u_long rmx_recvpipe; /* inbound delay-bandwith product */ 223 u_long rmx_sendpipe; /* outbound delay-bandwith product */ 224 u_long rmx_ssthresh; /* outbound gateway buffer limit */ 225 u_long rmx_rtt; /* estimated round trip time */ 226 u_long rmx_rttvar; /* estimated rtt variance */ 227}; 228.Ed 229.Pp 230Flags include the values: 231.Bd -literal 232#define RTF_UP 0x1 /* route useable */ 233#define RTF_GATEWAY 0x2 /* destination is a gateway */ 234#define RTF_HOST 0x4 /* host entry (net otherwise) */ 235#define RTF_NORMAL 0x8 /* subnet mask is cannonical */ 236#define RTF_DYNAMIC 0x10 /* created dynamically (by redirect) */ 237#define RTF_MODIFIED 0x20 /* modified dynamically (by redirect) */ 238#define RTF_DONE 0x40 /* message confirmed */ 239#define RTF_MASK 0x80 /* subnet mask present */ 240.Ed 241.Pp 242Specfiers for metric values in rmx_locks and rtm_inits are: 243.Bd -literal 244#define RTV_SSTHRESH 0x1 /* init or lock _ssthresh */ 245#define RTV_RPIPE 0x2 /* init or lock _recvpipe */ 246#define RTV_SPIPE 0x4 /* init or lock _sendpipe */ 247#define RTV_HOPCOUNT 0x8 /* init or lock _hopcount */ 248#define RTV_RTT 0x10 /* init or lock _rtt */ 249#define RTV_RTTVAR 0x20 /* init or lock _rttvar */ 250#define RTV_MTU 0x40 /* init or lock _mtu */ 251.Ed 252.Pp 253Specifiers for which addresses are present in the messages are: 254.Bd -literal 255#define RTA_DST 0x1 /* destination sockaddr present */ 256#define RTA_GATEWAY 0x2 /* gateway sockaddr present */ 257#define RTA_NETMASK 0x4 /* netmask sockaddr present */ 258#define RTA_GENMASK 0x8 /* cloning mask sockaddr present */ 259#define RTA_IFP 0x10 /* interface name sockaddr present */ 260#define RTA_IFA 0x20 /* interface addr sockaddr present */ 261#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */ 262.Ed 263.Sh HISTORY 264The 265.Nm 266forwarding database 267.Ud 268