1 Protocols route(7P)
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3
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5 NAME
6 route - kernel packet forwarding database
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8 SYNOPSIS
9 #include <sys/types.h>
10 #include <sys/socket.h>
11 #include <net/if.h>
12 #include <net/route.h>
13
14 int socket(PF_ROUTE, SOCK_RAW, int protocol);
15
16
17 DESCRIPTION
18 UNIX provides some packet routing facilities. The kernel
19 maintains a routing information database, which is used in
20 selecting the appropriate network interface when transmit-
21 ting packets.
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23
24 A user process (or possibly multiple co-operating processes)
25 maintains this database by sending messages over a special
26 kind of socket. This supplants fixed size ioctl(2)'s speci-
27 fied in routing(7P). Routing table changes may only be car-
28 ried out by the superuser.
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31 The operating system may spontaneously emit routing messages
32 in response to external events, such as receipt of a re-
33 direct, or failure to locate a suitable route for a request.
34 The message types are described in greater detail below.
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36
37 Routing database entries come in two flavors: entries for a
38 specific host, or entries for all hosts on a generic subnet-
39 work (as specified by a bit mask and value under the mask).
40 The effect of wildcard or default route may be achieved by
41 using a mask of all zeros, and there may be hierarchical
42 routes.
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44
45 When the system is booted and addresses are assigned to the
46 network interfaces, the internet protocol family installs a
47 routing table entry for each interface when it is ready for
48 traffic. Normally the protocol specifies the route through
49 each interface as a direct connection to the destination
50 host or network. If the route is direct, the transport
51 layer of a protocol family usually requests the packet be
52 sent to the same host specified in the packet. Otherwise,
53 the interface is requested to address the packet to the
54 gateway listed in the routing entry, that is, the packet is
55 forwarded.
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67 Protocols route(7P)
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71 When routing a packet, the kernel attempts to find the most
72 specific route matching the destination. If no entry is
73 found, the destination is declared to be unreachable, and a
74 routing-miss message is generated if there are any listeners
75 on the routing control socket (described below). If there
76 are two different mask and value-under-the-mask pairs that
77 match, the more specific is the one with more bits in the
78 mask. A route to a host is regarded as being supplied with a
79 mask of as many ones as there are bits in the destination.
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81
82 A wildcard routing entry is specified with a zero destina-
83 tion address value, and a mask of all zeroes. Wildcard
84 routes are used when the system fails to find other routes
85 matching the destination. The combination of wildcard routes
86 and routing redirects can provide an economical mechanism
87 for routing traffic.
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90 One opens the channel for passing routing control messages
91 by using the socket call shown in the section above. There
92 can be more than one routing socket open per system.
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95 Messages are formed by a header followed by a small number
96 of sockaddrs, whose length depend on the address family.
97 sockaddrs are interpreted by position. An example of a type
98 of message with three addresses might be a CIDR prefix
99 route: Destination, Netmask, and Gateway. The interpretation
100 of which addresses are present is given by a bit mask within
101 the header, and the sequence is least significant to most
102 significant bit within the vector.
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105 Any messages sent to the kernel are returned, and copies are
106 sent to all interested listeners. The kernel provides the
107 process ID of the sender, and the sender may use an addi-
108 tional sequence field to distinguish between outstanding
109 messages. However, message replies may be lost when kernel
110 buffers are exhausted.
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113 The protocol parameter specifies which messages an applica-
114 tion listening on the routing socket is interested in see-
115 ing, based on the the address family of the sockaddrs
116 present. Currently, you can specify AF_INET and AF_INET6 to
117 filter the messages seen by the listener, or alternatively,
118 you can specify AF_UNSPEC to indicate that the listener is
119 interested in all routing messages.
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133 Protocols route(7P)
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137 The kernel may reject certain messages, and will indicate
138 this by filling in the rtm_errno field of the rt_msghdr
139 struct (see below). The following codes may be returned:
140
141 EEXIST If requested to duplicate an existing entry
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144 ESRCH If requested to delete a non-existent entry
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146
147 ENOBUFS If insufficient resources were available to
148 install a new route.
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151 EPERM If the calling process does not have appropriate
152 privileges to alter the routing table.
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156 In the current implementation, all routing processes run
157 locally, and the values for rtm_errno are available through
158 the normal errno mechanism, even if the routing reply mes-
159 sage is lost.
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162 A process may avoid the expense of reading replies to its
163 own messages by issuing a setsockopt(3SOCKET) call indicat-
164 ing that the SO_USELOOPBACK option at the SOL_SOCKET level
165 is to be turned off. A process may ignore all messages from
166 the routing socket by doing a shutdown(3SOCKET) system call
167 for further input.
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170 If a route is in use when it is deleted, the routing entry
171 is marked down and removed from the routing table, but the
172 resources associated with it are not reclaimed until all
173 references to it are released.
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176 The RTM_IFINFO, RTM_NEWADDR, and RTM_ADD messages associated
177 with interface configuration (setting the IFF_UP bit) are
178 normally delayed until after Duplicate Address Detection
179 completes. Thus, applications that configure interfaces and
180 wish to wait until the interface is ready can wait until
181 RTM_IFINFO is returned and SIOCGLIFFLAGS shows that
182 IFF_DUPLICATE is not set.
183
184 Messages
185 User processes can obtain information about the routing
186 entry to a specific destination by using a RTM_GET message.
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199 Protocols route(7P)
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203 Messages include:
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205 #define RTM_ADD 0x1 /* Add Route */
206 #define RTM_DELETE 0x2 /* Delete Route */
207 #define RTM_CHANGE 0x3 /* Change Metrics, Flags, or Gateway */
208 #define RTM_GET 0x4 /* Report Information */
209 #define RTM_LOSING 0x5 /* Kernel Suspects Partitioning */
210 #define RTM_REDIRECT 0x6 /* Told to use different route */
211 #define RTM_MISS 0x7 /* Lookup failed on this address */
212 #define RTM_LOCK 0x8 /* fix specified metrics */
213 #define RTM_OLDADD 0x9 /* caused by SIOCADDRT */
214 #define RTM_OLDDEL 0xa /* caused by SIOCDELRT */
215 #define RTM_RESOLVE 0xb /* request to resolve dst to LL addr */
216 #define RTM_NEWADDR 0xc /* address being added to iface */
217 #define RTM_DELADDR 0xd /* address being removed from iface */
218 #define RTM_IFINFO 0xe /* iface going up/down etc. */
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222 A message header consists of:
223
224 struct rt_msghdr {
225 ushort_t rtm_msglen; /* to skip over non-understood messages */
226 uchar_t rtm_version; /* future binary compatibility */
227 uchar_t rtm_type; /* message type */
228 ushort_t rtm_index; /* index for associated ifp */
229 pid_t rtm_pid; /* identify sender */
230 int rtm_addrs; /* bitmask identifying sockaddrs in msg */
231 int rtm_seq; /* for sender to identify action */
232 int rtm_errno; /* why failed */
233 int rtm_flags; /* flags, incl kern & message, e.g., DONE */
234 int rtm_use; /* from rtentry */
235 uint_t rtm_inits; /* which values we are initializing */
236
237 struct rt_metrics rtm_rmx; /* metrics themselves */
238 };
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240
241
242 where
243
244 struct rt_metrics {
245 uint32_t rmx_locks; /* Kernel must leave these values alone */
246 uint32_t rmx_mtu; /* MTU for this path */
247 uint32_t rmx_hopcount; /* max hops expected */
248 uint32_t rmx_expire; /* lifetime for route, e.g., redirect */
249 uint32_t rmx_recvpipe; /* inbound delay-bandwidth product */
250 uint32_t rmx_sendpipe; /* outbound delay-bandwidth product */
251 uint32_t rmx_ssthresh; /* outbound gateway buffer limit */
252 uint32_t rmx_rtt; /* estimated round trip time */
253 uint32_t rmx_rttvar; /* estimated rtt variance */
254 uint32_t rmx_pksent; /* packets sent using this route */
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265 Protocols route(7P)
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269 };
270
271 /* Flags include the values */
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274 #define RTF_UP 0x1 /* route usable */
275 #define RTF_GATEWAY 0x2 /* destination is a gateway */
276 #define RTF_HOST 0x4 /* host entry (net otherwise) */
277 #define RTF_REJECT 0x8 /* host or net unreachable */
278 #define RTF_DYNAMIC 0x10 /* created dynamically(by redirect) */
279 #define RTF_MODIFIED 0x20 /* modified dynamically(by redirect) */
280 #define RTF_DONE 0x40 /* message confirmed */
281 #define RTF_MASK 0x80 /* subnet mask present */
282 #define RTF_CLONING 0x100 /* generate new routes on use */
283 #define RTF_XRESOLVE 0x200 /* external daemon resolves name */
284 #define RTF_LLINFO 0x400 /* generated by ARP */
285 #define RTF_STATIC 0x800 /* manually added */
286 #define RTF_BLACKHOLE 0x1000 /* just discard pkts (during updates) */
287 #define RTF_PRIVATE 0x2000 /* do not advertise this route */
288 #define RTF_PROTO2 0x4000 /* protocol specific routing flag #2 */
289 #define RTF_PROTO1 0x8000 /* protocol specific routing flag #1 */
290
291 /* Specifiers for metric values in rmx_locks and rtm_inits are */
292
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
302 /* Specifiers for which addresses are present in the messages are */
303
304 #define RTA_DST 0x1 /* destination sockaddr present */
305 #define RTA_GATEWAY 0x2 /* gateway sockaddr present */
306 #define RTA_NETMASK 0x4 /* netmask sockaddr present */
307 #define RTA_GENMASK 0x8 /* cloning mask sockaddr present */
308 #define RTA_IFP 0x10 /* interface name sockaddr present */
309 #define RTA_IFA 0x20 /* interface addr sockaddr present */
310 #define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */
311 #define RTA_BRD 0x80 /* for NEWADDR, broadcast or p-p dest addr */
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313
314 SEE ALSO
315 ioctl(2), setsockopt(3SOCKET), shutdown(3SOCKET),
316 routing(7P)
317
318 NOTES
319 Some of the metrics may not be implemented and return zero.
320 The implemented metrics are set in rtm_inits.
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