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1.\" $NetBSD: route.4,v 1.3 1994/11/30 16:22:31 jtc Exp $
2.\"
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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
49Mac OS X provides 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 receipt 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 attempt to find
88the most specific route matching the destination.
89(If there are two different mask and value-under-the-mask pairs
90that match, the more specific is the one with more bits in the mask.
91A route to a host is regarded as being supplied with a mask of
92as many ones as there are bits in the destination).
93If no entry is found, the destination is declared to be unreachable,
94and a routing\-miss message is generated if there are any
95listers on the routing control socket described below.
96.Pp
97A wildcard routing entry is specified with a zero
98destination address value, and a mask of all zeroes.
99Wildcard routes will be used
100when the system fails to find other routes matching the
101destination. The combination of wildcard
102routes and routing redirects can provide an economical
103mechanism for routing traffic.
104.Pp
105One opens the channel for passing routing control messages
106by using the socket call shown in the synopsis above:
107.Pp
108The
109.Fa family
110parameter may be
111.Dv AF_UNSPEC
112which will provide
113routing information for all address families, or can be restricted
114to a specific address family by specifying which one is desired.
115There can be more than one routing socket open per system.
116.Pp
117Messages are formed by a header followed by a small
118number of sockadders (now variable length particularly
119in the
120.Tn ISO
121case), interpreted by position, and delimited
122by the new length entry in the sockaddr.
123An example of a message with four addresses might be an
124.Tn ISO
125redirect:
126Destination, Netmask, Gateway, and Author of the redirect.
127The interpretation of which address are present is given by a
128bit mask within the header, and the sequence is least significant
129to most significant bit within the vector.
130.Pp
131Any messages sent to the kernel are returned, and copies are sent
132to all interested listeners. The kernel will provide the process
133id. for the sender, and the sender may use an additional sequence
134field to distinguish between outstanding messages. However,
135message replies may be lost when kernel buffers are exhausted.
136.Pp
137The kernel may reject certain messages, and will indicate this
138by filling in the
139.Ar rtm_errno
140field.
141The routing code returns
142.Dv EEXIST
143if
144requested to duplicate an existing entry,
145.Dv ESRCH
146if
147requested to delete a non-existent entry,
148or
149.Dv ENOBUFS
150if insufficient resources were available
151to install a new route.
152In the current implementation, all routing process run locally,
153and the values for
154.Ar rtm_errno
155are available through the normal
156.Em errno
157mechanism, even if the routing reply message is lost.
158.Pp
159A process may avoid the expense of reading replies to
160its own messages by issuing a
161.Xr setsockopt 2
162call indicating that the
163.Dv SO_USELOOPBACK
164option
165at the
166.Dv SOL_SOCKET
167level is to be turned off.
168A process may ignore all messages from the routing socket
169by doing a
170.Xr shutdown 2
171system call for further input.
172.Pp
173If a route is in use when it is deleted,
174the routing entry will be marked down and removed from the routing table,
175but the resources associated with it will not
176be reclaimed until all references to it are released.
177User processes can obtain information about the routing
178entry to a specific destination by using a
179.Dv RTM_GET
2d21ac55 180message.
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181.Pp
182Messages 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
194A message header consists of:
195.Bd -literal
196struct rt_msghdr {
b0d623f7 197 u_short rtm_msglen; /* to skip over non-understood messages */
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198 u_char rtm_version; /* future binary compatibility */
199 u_char rtm_type; /* message type */
b0d623f7
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200 u_short rtm_index; /* index for associated ifp or interface scope */
201 pid_t rtm_pid; /* identify sender */
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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
212where
213.Bd -literal
214struct 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
227Flags 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 */
b0d623f7 244#define RTF_IFSCOPE 0x1000000 /* has valid interface scope */
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245.Ed
246.Pp
247Specifiers for metric values in rmx_locks and rtm_inits are:
248.Bd -literal
249#define RTV_SSTHRESH 0x1 /* init or lock _ssthresh */
250#define RTV_RPIPE 0x2 /* init or lock _recvpipe */
251#define RTV_SPIPE 0x4 /* init or lock _sendpipe */
252#define RTV_HOPCOUNT 0x8 /* init or lock _hopcount */
253#define RTV_RTT 0x10 /* init or lock _rtt */
254#define RTV_RTTVAR 0x20 /* init or lock _rttvar */
255#define RTV_MTU 0x40 /* init or lock _mtu */
256.Ed
257.Pp
258Specifiers for which addresses are present in the messages are:
259.Bd -literal
260#define RTA_DST 0x1 /* destination sockaddr present */
261#define RTA_GATEWAY 0x2 /* gateway sockaddr present */
262#define RTA_NETMASK 0x4 /* netmask sockaddr present */
263#define RTA_GENMASK 0x8 /* cloning mask sockaddr present */
264#define RTA_IFP 0x10 /* interface name sockaddr present */
265#define RTA_IFA 0x20 /* interface addr sockaddr present */
266#define RTA_AUTHOR 0x40 /* sockaddr for author of redirect */
267.Ed