1.\" $NetBSD: route.4,v 1.6 1997/03/11 02:14:25 cjs Exp $ 2.\" 3.\" Copyright (c) 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)route.4 8.6 (Berkeley) 4/19/94 35.\" 36.Dd April 19, 1994 37.Dt ROUTE 4 38.Os 39.Sh NAME 40.Nm route 41.Nd kernel packet forwarding database 42.Sh SYNOPSIS 43.Fd #include <sys/socket.h> 44.Fd #include <net/if.h> 45.Fd #include <net/route.h> 46.Ft int 47.Fn socket PF_ROUTE SOCK_RAW "int family" 48.Sh DESCRIPTION 49.Tn UNIX 50provides some packet routing facilities. 51The kernel maintains a routing information database, which 52is used in selecting the appropriate network interface when 53transmitting packets. 54.Pp 55A user process (or possibly multiple co-operating processes) 56maintains this database by sending messages over a special kind 57of socket. 58This supplants fixed size 59.Xr ioctl 2 Ns 's 60used in earlier releases. 61Routing table changes may only be carried out by the super user. 62.Pp 63The operating system may spontaneously emit routing messages in response 64to external events, such as receipt of a re-direct, or failure to 65locate a suitable route for a request. 66The message types are described in greater detail below. 67.Pp 68Routing database entries come in two flavors: for a specific 69host, or for all hosts on a generic subnetwork (as specified 70by a bit mask and value under the mask. 71The effect of wildcard or default route may be achieved by using 72a mask of all zeros, and there may be hierarchical routes. 73.Pp 74When the system is booted and addresses are assigned 75to the network interfaces, each protocol family 76installs a routing table entry for each interface when it is ready for traffic. 77Normally the protocol specifies the route 78through each interface as a 79.Dq direct 80connection to the destination host 81or network. If the route is direct, the transport layer of 82a protocol family usually requests the packet be sent to the 83same host specified in the packet. Otherwise, the interface 84is requested to address the packet to the gateway listed in the routing entry 85(i.e. the packet is forwarded). 86.Pp 87When routing a packet, 88the kernel will attempt to find 89the most specific route matching the destination. 90(If there are two different mask and value-under-the-mask pairs 91that match, the more specific is the one with more bits in the mask. 92A route to a host is regarded as being supplied with a mask of 93as many ones as there are bits in the destination). 94If no entry is found, the destination is declared to be unreachable, 95and a routing\-miss message is generated if there are any 96listers on the routing control socket described below. 97.Pp 98A wildcard routing entry is specified with a zero 99destination address value, and a mask of all zeroes. 100Wildcard routes will be used 101when the system fails to find other routes matching the 102destination. The combination of wildcard 103routes and routing redirects can provide an economical 104mechanism for routing traffic. 105.Pp 106One opens the channel for passing routing control messages 107by using the socket call shown in the synopsis above: 108.Pp 109The 110.Fa family 111parameter may be 112.Dv AF_UNSPEC 113which will provide 114routing information for all address families, or can be restricted 115to a specific address family by specifying which one is desired. 116There can be more than one routing socket open per system. 117.Pp 118Messages are formed by a header followed by a small 119number of sockaddrs (now variable length particularly 120in the 121.Tn ISO 122case), interpreted by position, and delimited 123by the new length entry in the sockaddr. 124An example of a message with four addresses might be an 125.Tn ISO 126redirect: 127Destination, Netmask, Gateway, and Author of the redirect. 128The interpretation of which address are present is given by a 129bit mask within the header, and the sequence is least significant 130to most significant bit within the vector. 131.Pp 132Any messages sent to the kernel are returned, and copies are sent 133to all interested listeners. The kernel will provide the process 134ID for the sender, and the sender may use an additional sequence 135field to distinguish between outstanding messages. However, 136message replies may be lost when kernel buffers are exhausted. 137.Pp 138The kernel may reject certain messages, and will indicate this 139by filling in the 140.Ar rtm_errno 141field. 142The routing code returns 143.Dv EEXIST 144if 145requested to duplicate an existing entry, 146.Dv ESRCH 147if 148requested to delete a non-existent entry, 149or 150.Dv ENOBUFS 151if insufficient resources were available 152to install a new route. 153In the current implementation, all routing processes run locally, 154and the values for 155.Ar rtm_errno 156are available through the normal 157.Em errno 158mechanism, even if the routing reply message is lost. 159.Pp 160A process may avoid the expense of reading replies to 161its own messages by issuing a 162.Xr setsockopt 2 163call indicating that the 164.Dv SO_USELOOPBACK 165option 166at the 167.Dv SOL_SOCKET 168level is to be turned off. 169A process may ignore all messages from the routing socket 170by doing a 171.Xr shutdown 2 172system call for further input. 173.Pp 174If a route is in use when it is deleted, 175the routing entry will be marked down and removed from the routing table, 176but the resources associated with it will not 177be reclaimed until all references to it are released. 178User processes can obtain information about the routing 179entry to a specific destination by using a 180.Dv RTM_GET 181message, 182or by reading the 183.Pa /dev/kmem 184device, or by calling 185.Xr sysctl 3 . 186.Pp 187The messages are: 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_LOSING 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#define RTM_NEWADDR 0xc /* address being added to iface */ 198#define RTM_DELADDR 0xd /* address being removed from iface */ 199#define RTM_IFINFO 0xe /* iface going up/down etc. */ 200.Ed 201.Pp 202A message header consists of one of the following: 203.Bd -literal 204struct rt_msghdr { 205 u_short rtm_msglen; /* to skip over non-understood messages */ 206 u_char rtm_version; /* future binary compatibility */ 207 u_char rtm_type; /* message type */ 208 u_short rtm_index; /* index for associated ifp */ 209 int rtm_flags; /* flags, incl kern & message, e.g. DONE */ 210 int rtm_addrs; /* bitmask identifying sockaddrs in msg */ 211 pid_t rtm_pid; /* identify sender */ 212 int rtm_seq; /* for sender to identify action */ 213 int rtm_errno; /* why failed */ 214 int rtm_use; /* from rtentry */ 215 u_long rtm_inits; /* which metrics we are initializing */ 216 struct rt_metrics rtm_rmx; /* metrics themselves */ 217}; 218 219struct if_msghdr { 220 u_short ifm_msglen; /* to skip over non-understood messages */ 221 u_char ifm_version; /* future binary compatability */ 222 u_char ifm_type; /* message type */ 223 int ifm_addrs; /* like rtm_addrs */ 224 int ifm_flags; /* value of if_flags */ 225 u_short ifm_index; /* index for associated ifp */ 226 struct if_data ifm_data; /* statistics and other data about if */ 227}; 228 229struct ifa_msghdr { 230 u_short ifam_msglen; /* to skip over non-understood messages */ 231 u_char ifam_version; /* future binary compatability */ 232 u_char ifam_type; /* message type */ 233 int ifam_addrs; /* like rtm_addrs */ 234 int ifam_flags; /* value of ifa_flags */ 235 u_short ifam_index; /* index for associated ifp */ 236 int ifam_metric; /* value of ifa_metric */ 237}; 238.Ed 239.Pp 240The 241.Dv RTM_IFINFO 242message uses a 243.Ar if_msghdr 244header, the 245.Dv RTM_NEWADDR 246and 247.Dv RTM_DELADDR 248messages use a 249.Ar ifa_msghdr 250header, and all other messages use the 251.Ar rt_msghdr 252header. 253.Pp 254The metrics structure is: 255.Bd -literal 256struct rt_metrics { 257 u_long rmx_locks; /* Kernel must leave these values alone */ 258 u_long rmx_mtu; /* MTU for this path */ 259 u_long rmx_hopcount; /* max hops expected */ 260 u_long rmx_expire; /* lifetime for route, e.g. redirect */ 261 u_long rmx_recvpipe; /* inbound delay-bandwith product */ 262 u_long rmx_sendpipe; /* outbound delay-bandwith product */ 263 u_long rmx_ssthresh; /* outbound gateway buffer limit */ 264 u_long rmx_rtt; /* estimated round trip time */ 265 u_long rmx_rttvar; /* estimated rtt variance */ 266 u_long rmx_pksent; /* packets sent using this route */ 267}; 268.Ed 269.Pp 270Flags include the values: 271.Bd -literal 272#define RTF_UP 0x1 /* route usable */ 273#define RTF_GATEWAY 0x2 /* destination is a gateway */ 274#define RTF_HOST 0x4 /* host entry (net otherwise) */ 275#define RTF_REJECT 0x8 /* host or net unreachable */ 276#define RTF_DYNAMIC 0x10 /* created dynamically (by redirect) */ 277#define RTF_MODIFIED 0x20 /* modified dynamically (by redirect) */ 278#define RTF_DONE 0x40 /* message confirmed */ 279#define RTF_MASK 0x80 /* subnet mask present */ 280#define RTF_CLONING 0x100 /* generate new routes on use */ 281#define RTF_XRESOLVE 0x200 /* external daemon resolves name */ 282#define RTF_LLINFO 0x400 /* generated by ARP or ESIS */ 283#define RTF_STATIC 0x800 /* manually added */ 284#define RTF_BLACKHOLE 0x1000 /* just discard pkts (during updates) */ 285#define RTF_PROTO2 0x4000 /* protocol specific routing flag */ 286#define RTF_PROTO1 0x8000 /* protocol specific routing flag */ 287.Ed 288.Pp 289Specifiers for metric values in rmx_locks and rtm_inits are: 290.Bd -literal 291#define RTV_MTU 0x1 /* init or lock _mtu */ 292#define RTV_HOPCOUNT 0x2 /* init or lock _hopcount */ 293#define RTV_EXPIRE 0x4 /* init or lock _expire */ 294#define RTV_RPIPE 0x8 /* init or lock _recvpipe */ 295#define RTV_SPIPE 0x10 /* init or lock _sendpipe */ 296#define RTV_SSTHRESH 0x20 /* init or lock _ssthresh */ 297#define RTV_RTT 0x40 /* init or lock _rtt */ 298#define RTV_RTTVAR 0x80 /* init or lock _rttvar */ 299.Ed 300.Pp 301Specifiers for which addresses are present in the messages are: 302.Bd -literal 303#define RTA_DST 0x1 /* destination sockaddr present */ 304#define RTA_GATEWAY 0x2 /* gateway sockaddr present */ 305#define RTA_NETMASK 0x4 /* netmask sockaddr present */ 306#define RTA_GENMASK 0x8 /* cloning mask sockaddr present */ 307#define RTA_IFP 0x10 /* interface name sockaddr present */ 308#define RTA_IFA 0x20 /* interface addr sockaddr present */ 309#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */ 310#define RTA_BRD 0x80 /* for NEWADDR, broadcast or p-p dest addr */ 311.Ed 312.Sh SEE ALSO 313.Xr socket 2 , 314.Xr sysctl 3 315