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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: src/share/man/man4/route.4,v 1.9.2.6 2002/03/17 09:12:44 schweikh Exp $ 34.\" $DragonFly: src/share/man/man4/route.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 35.\" 36.Dd January 18, 2002 37.Dt ROUTE 4 38.Os 39.Sh NAME 40.Nm route 41.Nd kernel packet forwarding database 42.Sh SYNOPSIS 43.In sys/types.h 44.In sys/time.h 45.In sys/socket.h 46.In net/if.h 47.In net/route.h 48.Ft int 49.Fn socket PF_ROUTE SOCK_RAW "int family" 50.Sh DESCRIPTION 51.Fx 52provides some packet routing facilities. 53The kernel maintains a routing information database, which 54is used in selecting the appropriate network interface when 55transmitting packets. 56.Pp 57A user process (or possibly multiple co-operating processes) 58maintains this database by sending messages over a special kind 59of socket. 60This supplants fixed size 61.Xr ioctl 2 Ns 's 62used in earlier releases. 63Routing table changes may only be carried out by the super user. 64.Pp 65The operating system may spontaneously emit routing messages in response 66to external events, such as receipt of a re-direct, or failure to 67locate a suitable route for a request. 68The message types are described in greater detail below. 69.Pp 70Routing database entries come in two flavors: for a specific 71host, or for all hosts on a generic subnetwork (as specified 72by a bit mask and value under the mask. 73The effect of wildcard or default route may be achieved by using 74a mask of all zeros, and there may be hierarchical routes. 75.Pp 76When the system is booted and addresses are assigned 77to the network interfaces, each protocol family 78installs a routing table entry for each interface when it is ready for traffic. 79Normally the protocol specifies the route 80through each interface as a 81.Dq direct 82connection to the destination host 83or network. If the route is direct, the transport layer of 84a protocol family usually requests the packet be sent to the 85same host specified in the packet. Otherwise, the interface 86is requested to address the packet to the gateway listed in the routing entry 87(i.e. the packet is forwarded). 88.Pp 89When routing a packet, 90the kernel will attempt to find 91the most specific route matching the destination. 92(If there are two different mask and value-under-the-mask pairs 93that match, the more specific is the one with more bits in the mask. 94A route to a host is regarded as being supplied with a mask of 95as many ones as there are bits in the destination). 96If no entry is found, the destination is declared to be unreachable, 97and a routing\-miss message is generated if there are any 98listeners on the routing control socket described below. 99.Pp 100A wildcard routing entry is specified with a zero 101destination address value, and a mask of all zeroes. 102Wildcard routes will be used 103when the system fails to find other routes matching the 104destination. The combination of wildcard 105routes and routing redirects can provide an economical 106mechanism for routing traffic. 107.Pp 108One opens the channel for passing routing control messages 109by using the socket call shown in the synopsis above: 110.Pp 111The 112.Fa family 113parameter may be 114.Dv AF_UNSPEC 115which will provide 116routing information for all address families, or can be restricted 117to a specific address family by specifying which one is desired. 118There can be more than one routing socket open per system. 119.Pp 120Messages are formed by a header followed by a small 121number of sockaddrs (now variable length particularly 122in the 123.Tn ISO 124case), interpreted by position, and delimited 125by the new length entry in the sockaddr. 126An example of a message with four addresses might be an 127.Tn ISO 128redirect: 129Destination, Netmask, Gateway, and Author of the redirect. 130The interpretation of which address are present is given by a 131bit mask within the header, and the sequence is least significant 132to most significant bit within the vector. 133.Pp 134Any messages sent to the kernel are returned, and copies are sent 135to all interested listeners. The kernel will provide the process 136ID for the sender, and the sender may use an additional sequence 137field to distinguish between outstanding messages. However, 138message replies may be lost when kernel buffers are exhausted. 139.Pp 140The kernel may reject certain messages, and will indicate this 141by filling in the 142.Ar rtm_errno 143field. 144The routing code returns 145.Er EEXIST 146if 147requested to duplicate an existing entry, 148.Er ESRCH 149if 150requested to delete a non-existent entry, 151or 152.Er ENOBUFS 153if insufficient resources were available 154to install a new route. 155In the current implementation, all routing processes run locally, 156and the values for 157.Ar rtm_errno 158are available through the normal 159.Em errno 160mechanism, even if the routing reply message is lost. 161.Pp 162A process may avoid the expense of reading replies to 163its own messages by issuing a 164.Xr setsockopt 2 165call indicating that the 166.Dv SO_USELOOPBACK 167option 168at the 169.Dv SOL_SOCKET 170level is to be turned off. 171A process may ignore all messages from the routing socket 172by doing a 173.Xr shutdown 2 174system call for further input. 175.Pp 176If a route is in use when it is deleted, 177the routing entry will be marked down and removed from the routing table, 178but the resources associated with it will not 179be reclaimed until all references to it are released. 180User processes can obtain information about the routing 181entry to a specific destination by using a 182.Dv RTM_GET 183message, or by calling 184.Xr sysctl 3 . 185.Pp 186Messages include: 187.Bd -literal 188#define RTM_ADD 0x1 /* Add Route */ 189#define RTM_DELETE 0x2 /* Delete Route */ 190#define RTM_CHANGE 0x3 /* Change Metrics, Flags, or Gateway */ 191#define RTM_GET 0x4 /* Report Information */ 192#define RTM_LOSING 0x5 /* Kernel Suspects Partitioning */ 193#define RTM_REDIRECT 0x6 /* Told to use different route */ 194#define RTM_MISS 0x7 /* Lookup failed on this address */ 195#define RTM_LOCK 0x8 /* fix specified metrics */ 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#define RTM_NEWMADDR 0xf /* mcast group membership being added to if */ 201#define RTM_DELMADDR 0x10 /* mcast group membership being deleted */ 202#define RTM_IFANNOUNCE 0x11 /* iface arrival/departure */ 203.Ed 204.Pp 205A message header consists of one of the following: 206.Bd -literal 207struct rt_msghdr { 208 u_short rtm_msglen; /* to skip over non-understood messages */ 209 u_char rtm_version; /* future binary compatibility */ 210 u_char rtm_type; /* message type */ 211 u_short rtm_index; /* index for associated ifp */ 212 int rtm_flags; /* flags, incl. kern & message, e.g. DONE */ 213 int rtm_addrs; /* bitmask identifying sockaddrs in msg */ 214 pid_t rtm_pid; /* identify sender */ 215 int rtm_seq; /* for sender to identify action */ 216 int rtm_errno; /* why failed */ 217 int rtm_use; /* from rtentry */ 218 u_long rtm_inits; /* which metrics we are initializing */ 219 struct rt_metrics rtm_rmx; /* metrics themselves */ 220}; 221 222struct if_msghdr { 223 u_short ifm_msglen; /* to skip over non-understood messages */ 224 u_char ifm_version; /* future binary compatibility */ 225 u_char ifm_type; /* message type */ 226 int ifm_addrs; /* like rtm_addrs */ 227 int ifm_flags; /* value of if_flags */ 228 u_short ifm_index; /* index for associated ifp */ 229 struct if_data ifm_data; /* statistics and other data about if */ 230}; 231 232struct ifa_msghdr { 233 u_short ifam_msglen; /* to skip over non-understood messages */ 234 u_char ifam_version; /* future binary compatibility */ 235 u_char ifam_type; /* message type */ 236 int ifam_addrs; /* like rtm_addrs */ 237 int ifam_flags; /* value of ifa_flags */ 238 u_short ifam_index; /* index for associated ifp */ 239 int ifam_metric; /* value of ifa_metric */ 240}; 241 242struct ifma_msghdr { 243 u_short ifmam_msglen; /* to skip over non-understood messages */ 244 u_char ifmam_version; /* future binary compatibility */ 245 u_char ifmam_type; /* message type */ 246 int ifmam_addrs; /* like rtm_addrs */ 247 int ifmam_flags; /* value of ifa_flags */ 248 u_short ifmam_index; /* index for associated ifp */ 249}; 250 251struct if_announcemsghdr { 252 u_short ifan_msglen; /* to skip over non-understood messages */ 253 u_char ifan_version; /* future binary compatibility */ 254 u_char ifan_type; /* message type */ 255 u_short ifan_index; /* index for associated ifp */ 256 char ifan_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 257 u_short ifan_what; /* what type of announcement */ 258}; 259.Ed 260.Pp 261The 262.Dv RTM_IFINFO 263message uses a 264.Ar if_msghdr 265header, the 266.Dv RTM_NEWADDR 267and 268.Dv RTM_DELADDR 269messages use a 270.Ar ifa_msghdr 271header, the 272.Dv RTM_NEWMADDR 273and 274.Dv RTM_DELMADDR 275messages use a 276.Vt ifma_msghdr 277header, the 278.Dv RTM_IFANNOUNCE 279message uses a 280.Vt if_announcemsghdr 281header, 282and all other messages use the 283.Ar rt_msghdr 284header. 285.Pp 286The 287.Dq Li "struct rt_metrics" 288and the flag bits are as defined in 289.Xr rtentry 9 . 290.Pp 291Specifiers for metric values in rmx_locks and rtm_inits are: 292.Bd -literal 293#define RTV_MTU 0x1 /* init or lock _mtu */ 294#define RTV_HOPCOUNT 0x2 /* init or lock _hopcount */ 295#define RTV_EXPIRE 0x4 /* init or lock _expire */ 296#define RTV_RPIPE 0x8 /* init or lock _recvpipe */ 297#define RTV_SPIPE 0x10 /* init or lock _sendpipe */ 298#define RTV_SSTHRESH 0x20 /* init or lock _ssthresh */ 299#define RTV_RTT 0x40 /* init or lock _rtt */ 300#define RTV_RTTVAR 0x80 /* init or lock _rttvar */ 301.Ed 302.Pp 303Specifiers for which addresses are present in the messages are: 304.Bd -literal 305#define RTA_DST 0x1 /* destination sockaddr present */ 306#define RTA_GATEWAY 0x2 /* gateway sockaddr present */ 307#define RTA_NETMASK 0x4 /* netmask sockaddr present */ 308#define RTA_GENMASK 0x8 /* cloning mask sockaddr present */ 309#define RTA_IFP 0x10 /* interface name sockaddr present */ 310#define RTA_IFA 0x20 /* interface addr sockaddr present */ 311#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */ 312#define RTA_BRD 0x80 /* for NEWADDR, broadcast or p-p dest addr */ 313.Ed 314.Sh SEE ALSO 315.Xr sysctl 3 , 316.Xr route 8 , 317.Xr rtentry 9 318.Sh HISTORY 319A 320.Dv PF_ROUTE 321protocol family first appeared in 322.Bx 4.3 reno . 323