bsd/man/man4/route.4

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  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 Mac OS X provides some packet routing facilities.
  50 The kernel maintains a routing information database, which
  51 is used in selecting the appropriate network interface when
  52 transmitting packets.
  53 .Pp
  54 A user process (or possibly multiple co-operating processes)
  55 maintains this database by sending messages over a special kind
  56 of socket.
  57 This supplants fixed size
  58 .Xr ioctl 2 Ns 's
  59 used in earlier releases.
  60 Routing table changes may only be carried out by the super user.
  61 .Pp
  62 The operating system may spontaneously emit routing messages in response
  63 to external events, such as receipt of a re-direct, or failure to
  64 locate a suitable route for a request.
  65 The message types are described in greater detail below.
  66 .Pp
  67 Routing database entries come in two flavors: for a specific
  68 host, or for all hosts on a generic subnetwork (as specified
  69 by a bit mask and value under the mask.
  70 The effect of wildcard or default route may be achieved by using
  71 a mask of all zeros, and there may be hierarchical routes.
  72 .Pp
  73 When the system is booted and addresses are assigned
  74 to the network interfaces, each protocol family
  75 installs a routing table entry for each interface when it is ready for traffic.
  76 Normally the protocol specifies the route
  77 through each interface as a
  78 .Dq direct
  79 connection to the destination host
  80 or network.  If the route is direct, the transport layer of
  81 a protocol family usually requests the packet be sent to the
  82 same host specified in the packet.  Otherwise, the interface
  83 is requested to address the packet to the gateway listed in the routing entry
  84 (i.e. the packet is forwarded).
  85 .Pp
  86 When routing a packet,
  87 the kernel will attempt to find
  88 the most specific route matching the destination.
  89 (If there are two different mask and value-under-the-mask pairs
  90 that match, the more specific is the one with more bits in the mask.
  91 A route to a host is regarded as being supplied with a mask of
  92 as many ones as there are bits in the destination).
  93 If no entry is found, the destination is declared to be unreachable,
  94 and a routing\-miss message is generated if there are any
  95 listers on the routing control socket described below.
  96 .Pp
  97 A wildcard routing entry is specified with a zero
  98 destination address value, and a mask of all zeroes.
  99 Wildcard routes will be used
 100 when the system fails to find other routes matching the
 101 destination.  The combination of wildcard
 102 routes and routing redirects can provide an economical
 103 mechanism for routing traffic.
 104 .Pp
 105 One opens the channel for passing routing control messages
 106 by using the socket call shown in the synopsis above:
 107 .Pp
 108 The
 109 .Fa family
 110 parameter may be
 111 .Dv AF_UNSPEC
 112 which will provide
 113 routing information for all address families, or can be restricted
 114 to a specific address family by specifying which one is desired.
 115 There can be more than one routing socket open per system.
 116 .Pp
 117 Messages are formed by a header followed by a small
 118 number of sockadders (now variable length particularly
 119 in the
 120 .Tn ISO
 121 case), interpreted by position, and delimited
 122 by the new length entry in the sockaddr.
 123 An example of a message with four addresses might be an
 124 .Tn ISO
 125 redirect:
 126 Destination, Netmask, Gateway, and Author of the redirect.
 127 The interpretation of which address are present is given by a
 128 bit mask within the header, and the sequence is least significant
 129 to most significant bit within the vector.
 130 .Pp
 131 Any messages sent to the kernel are returned, and copies are sent
 132 to all interested listeners.  The kernel will provide the process
 133 id. for the sender, and the sender may use an additional sequence
 134 field to distinguish between outstanding messages.  However,
 135 message replies may be lost when kernel buffers are exhausted.
 136 .Pp
 137 The kernel may reject certain messages, and will indicate this
 138 by filling in the
 139 .Ar rtm_errno
 140 field.
 141 The routing code returns
 142 .Dv EEXIST
 143 if
 144 requested to duplicate an existing entry,
 145 .Dv ESRCH
 146 if
 147 requested to delete a non-existent entry,
 148 or
 149 .Dv ENOBUFS
 150 if insufficient resources were available
 151 to install a new route.
 152 In the current implementation, all routing process run locally,
 153 and the values for
 154 .Ar rtm_errno
 155 are available through the normal
 156 .Em errno
 157 mechanism, even if the routing reply message is lost.
 158 .Pp
 159 A process may avoid the expense of reading replies to
 160 its own messages by issuing a
 161 .Xr setsockopt 2
 162 call indicating that the
 163 .Dv SO_USELOOPBACK
 164 option
 165 at the
 166 .Dv SOL_SOCKET
 167 level is to be turned off.
 168 A process may ignore all messages from the routing socket
 169 by doing a
 170 .Xr shutdown 2
 171 system call for further input.
 172 .Pp
 173 If a route is in use when it is deleted,
 174 the routing entry will be marked down and removed from the routing table,
 175 but the resources associated with it will not
 176 be reclaimed until all references to it are released.
 177 User processes can obtain information about the routing
 178 entry to a specific destination by using a
 179 .Dv RTM_GET
 180 message.
 181 .Pp
 182 Messages include:
 183 .Bd -literal
 184 #define RTM_ADD         0x1    /* Add Route */
 185 #define RTM_DELETE      0x2    /* Delete Route */
 186 #define RTM_CHANGE      0x3    /* Change Metrics, Flags, or Gateway */
 187 #define RTM_GET         0x4    /* Report Information */
 188 #define RTM_LOOSING     0x5    /* Kernel Suspects Partitioning */
 189 #define RTM_REDIRECT    0x6    /* Told to use different route */
 190 #define RTM_MISS        0x7    /* Lookup failed on this address */
 191 #define RTM_RESOLVE     0xb    /* request to resolve dst to LL addr */
 192 .Ed
 193 .Pp
 194 A message header consists of:
 195 .Bd -literal
 196 struct rt_msghdr {
 197     u_short rmt_msglen;  /* to skip over non-understood messages */
 198     u_char  rtm_version; /* future binary compatibility */
 199     u_char  rtm_type;    /* message type */
 200     u_short rmt_index;   /* index for associated ifp */
 201     pid_t   rmt_pid;     /* identify sender */
 202     int     rtm_addrs;   /* bitmask identifying sockaddrs in msg */
 203     int     rtm_seq;     /* for sender to identify action */
 204     int     rtm_errno;   /* why failed */
 205     int     rtm_flags;   /* flags, incl kern & message, e.g. DONE */
 206     int     rtm_use;     /* from rtentry */
 207     u_long  rtm_inits;   /* which values we are initializing */
 208     struct  rt_metrics rtm_rmx; /* metrics themselves */
 209 };
 210 .Ed
 211 .Pp
 212 where
 213 .Bd -literal
 214 struct rt_metrics {
 215     u_long rmx_locks;     /* Kernel must leave these values alone */
 216     u_long rmx_mtu;       /* MTU for this path */
 217     u_long rmx_hopcount;  /* max hops expected */
 218     u_long rmx_expire;    /* lifetime for route, e.g. redirect */
 219     u_long rmx_recvpipe;  /* inbound delay-bandwith product */
 220     u_long rmx_sendpipe;  /* outbound delay-bandwith product */
 221     u_long rmx_ssthresh;  /* outbound gateway buffer limit */
 222     u_long rmx_rtt;       /* estimated round trip time */
 223     u_long rmx_rttvar;    /* estimated rtt variance */
 224 };
 225 .Ed
 226 .Pp
 227 Flags include the values:
 228 .Bd -literal
 229 #define RTF_UP        0x1       /* route usable */
 230 #define RTF_GATEWAY   0x2       /* destination is a gateway */
 231 #define RTF_HOST      0x4       /* host entry (net otherwise) */
 232 #define RTF_REJECT    0x8       /* host or net unreachable */
 233 #define RTF_DYNAMIC   0x10      /* created dynamically (by redirect) */
 234 #define RTF_MODIFIED  0x20      /* modified dynamically (by redirect) */
 235 #define RTF_DONE      0x40      /* message confirmed */
 236 #define RTF_MASK      0x80      /* subnet mask present */
 237 #define RTF_CLONING   0x100     /* generate new routes on use */
 238 #define RTF_XRESOLVE  0x200     /* external daemon resolves name */
 239 #define RTF_LLINFO    0x400     /* generated by ARP or ESIS */
 240 #define RTF_STATIC    0x800     /* manually added */
 241 #define RTF_BLACKHOLE 0x1000    /* just discard pkts (during updates) */
 242 #define RTF_PROTO2    0x4000    /* protocol specific routing flag #1 */
 243 #define RTF_PROTO1    0x8000    /* protocol specific routing flag #2 */
 244 .Ed
 245 .Pp
 246 Specifiers for metric values in rmx_locks and rtm_inits are:
 247 .Bd -literal
 248 #define RTV_SSTHRESH  0x1    /* init or lock _ssthresh */
 249 #define RTV_RPIPE     0x2    /* init or lock _recvpipe */
 250 #define RTV_SPIPE     0x4    /* init or lock _sendpipe */
 251 #define RTV_HOPCOUNT  0x8    /* init or lock _hopcount */
 252 #define RTV_RTT       0x10   /* init or lock _rtt */
 253 #define RTV_RTTVAR    0x20   /* init or lock _rttvar */
 254 #define RTV_MTU       0x40   /* init or lock _mtu */
 255 .Ed
 256 .Pp
 257 Specifiers for which addresses are present in the messages are:
 258 .Bd -literal
 259 #define RTA_DST       0x1    /* destination sockaddr present */
 260 #define RTA_GATEWAY   0x2    /* gateway sockaddr present */
 261 #define RTA_NETMASK   0x4    /* netmask sockaddr present */
 262 #define RTA_GENMASK   0x8    /* cloning mask sockaddr present */
 263 #define RTA_IFP       0x10   /* interface name sockaddr present */
 264 #define RTA_IFA       0x20   /* interface addr sockaddr present */
 265 #define RTA_AUTHOR    0x40   /* sockaddr for author of redirect */
 266 .Ed