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31 .Dd October 8, 1996
32 .Dt RTENTRY 9
33 .Os
34 .Sh NAME
35 .Nm rtentry
36 .Nd structure of an entry in the kernel routing table
37 .Sh SYNOPSIS
38 .In sys/types.h
39 .In sys/socket.h
40 .In net/route.h
41 .Sh DESCRIPTION
42 The kernel provides a common mechanism by which all protocols can store
43 and retrieve entries from a central table of routes. Parts of this
44 mechanism are also used to interact with user-level processes by means
45 of a socket in the
46 .Xr route 4
47 pseudo-protocol family.
48 The
49 .In net/route.h
50 header file defines the structures and manifest constants used in this
51 facility.
52 .Pp
53 The basic structure of a route is defined by
54 .Dq Li struct rtentry ,
55 which includes the following fields:
56 .Bl -tag -offset indent -width 6n
57 .It Xo
58 .Vt "struct radix_node rt_nodes[2]" ;
59 .Xc
60 Glue used by the radix-tree routines. These members also include in
61 their substructure the key (i.e., destination address) and mask used
62 when the route was created. The
63 .Fn rt_key \&rt
64 and
65 .Fn rt_mask \&rt
66 macros can be used to extract this information (in the form of a
67 .Dq Li "struct sockaddr *" )
68 given a
69 .Li "struct rtentry *" .
70 .It Xo
71 .Vt "struct sockaddr *rt_gateway" ;
72 .Xc
73 The
74 .Dq target
75 of the route, which can either represent a destination in its own
76 right (some protocols will put a link-layer address here), or some
77 intermediate stop on the way to that destination (if the
78 .Dv RTF_GATEWAY
79 flag is set).
80 .It Xo
81 .Vt "long rt_refcnt" ;
82 .Xc
83 Route entries are reference-counted; this field indicates the number
84 of external (to the radix tree) references. If the
85 .Dv RTF_UP
86 flag is not present, the
87 .Fn rtfree
88 function will delete the route from the radix tree when the last
89 reference drops.
90 .It Xo
91 .Vt "u_long rt_flags" ;
92 .Xc
93 See below.
94 .It Xo
95 .Vt "struct ifnet *rt_ifp" ;
96 .Xc
97 .It Xo
98 .Vt "struct ifaddr *rt_ifa" ;
99 .Xc
100 These two fields represent the
101 .Dq answer ,
102 as it were, to the question posed by a route lookup; that is, they
103 name the interface and interface address to be used in sending a
104 packet to the destination or set of destinations which this route
105 represents.
106 .It Xo
107 .Vt "struct sockaddr *rt_genmask" ;
108 .Xc
109 When the
110 .Fn rtalloc
111 family of functions performs a cloning operation as requested by the
112 .Dv RTF_CLONING
113 or
114 .Dv RTF_PRCLONING
115 flag, this field is used as the mask for the new route which is
116 inserted into the table. If this field is a null pointer, then a host
117 route is generated.
118 .It Xo
119 .Vt "caddr_t rt_llinfo" ;
120 .Xc
121 When the
122 .Dv RTF_LLINFO
123 flag is set, this field contains information specific to the link
124 layer represented by the named interface address. (It is normally
125 managed by the
126 .Fn rt_ifa->ifa_rtrequest
127 routine.) Protocols such as
128 .Xr arp 4
129 use this field to reference per-destination state internal to that
130 protocol.
131 .It Xo
132 .Vt "struct rt_metrics rt_rmx" ;
133 .Xc
134 See below.
135 .It Xo
136 .Vt "struct rtentry *rt_gwroute" ;
137 .Xc
138 This member is a reference to a route whose destination is
139 .Li rt_gateway .
140 It is only used for
141 .Dv RTF_GATEWAY
142 routes.
143 .\" .It Dv "int (*rt_output)();"
144 .\" See below.
145 .It Xo
146 .Vt "struct rtentry *rt_parent" ;
147 .Xc
148 A reference to the route from which this route was cloned, or a null
149 pointer if this route was not generated by cloning. See also the
150 .Dv RTF_WASCLONED
151 flag.
152 .El
153 .Pp
154 The following flag bits are defined:
155 .Bl -tag -offset indent -width ".Dv RTF_BLACKHOLE" -compact
156 .It Dv RTF_UP
157 The route is not deleted.
158 .It Dv RTF_GATEWAY
159 The route points to an intermediate destination and not the ultimate
160 recipient; the
161 .Li rt_gateway
162 and
163 .Li rt_gwroute
164 fields name that destination.
165 .It Dv RTF_HOST
166 This is a host route.
167 .It Dv RTF_REJECT
168 The destination is presently unreachable. This should result in an
169 .Er EHOSTUNREACH
170 error from output routines.
171 .It Dv RTF_DYNAMIC
172 This route was created dynamically by
173 .Fn rtredirect .
174 .It Dv RTF_MODIFIED
175 This route was modified by
176 .Fn rtredirect .
177 .It Dv RTF_DONE
178 Used only in the
179 .Xr route 4
180 protocol, indicating that the request was executed.
181 .It Dv RTF_CLONING
182 When this route is returned as a result of a lookup, automatically
183 create a new route using this one as a template and
184 .Li rt_genmask
185 (if present) as a mask.
186 .It Dv RTF_XRESOLVE
187 When this route is returned as a result of a lookup, send a report on
188 the
189 .Xr route 4
190 interface requesting that an external process perform resolution for
191 this route. (Used in conjunction with
192 .Dv RTF_CLONING . )
193 .It Dv RTF_LLINFO
194 Indicates that this route represents information being managed by a
195 link layer's adaptation layer (e.g.,
196 .Tn ARP ) .
197 .It Dv RTF_STATIC
198 Indicates that this route was manually added by means of the
199 .Xr route 8
200 command.
201 .It Dv RTF_BLACKHOLE
202 Requests that output sent via this route be discarded.
203 .It Dv RTF_PROTO1
204 .It Dv RTF_PROTO2
205 .It Dv RTF_PROTO3
206 Protocol-specific.
207 .It Dv RTF_PRCLONING
208 Like
209 .Dv RTF_CLONING ,
210 only managed by an entire protocol. (E.g.,
211 .Tn IP
212 uses this flag to manage a per-host cache integrated with the routing
213 table, for those destinations which do not have a link layer
214 performing this function.)
215 .It Dv RTF_WASCLONED
216 Indicates that this route was generated as a result of cloning
217 requested by the
218 .Dv RTF_CLONING
219 or
220 .Dv RTF_PRCLONING
221 flag. When set, the
222 .Li rt_parent
223 field indicates the route from which this one was generated.
224 .It Dv RTF_PINNED
225 (Reserved for future use to indicate routes which are not to be
226 modified by a routing protocol.)
227 .It Dv RTF_LOCAL
228 Indicates that the destination of this route is an address configured
229 as belonging to this system.
230 .It Dv RTF_BROADCAST
231 Indicates that the destination is a broadcast address.
232 .It Dv RTF_MULTICAST
233 Indicates that the destination is a multicast address.
234 .El
235 .Pp
236 Every route has associated with it a set of metrics, defined by
237 .Li struct rt_metrics :
238 .Bl -tag -offset indent -width 6n
239 .It Xo
240 .Vt "u_long rmx_locks" ;
241 .Xc
242 Flag bits indicating which metrics the kernel is not permitted to
243 dynamically modify.
244 .It Xo
245 .Vt "u_long rmx_mtu" ;
246 .Xc
247 MTU for this path.
248 .It Xo
249 .Vt "u_long rmx_hopcount" ;
250 .Xc
251 Number of intermediate systems on the path to this destination.
252 .It Xo
253 .Vt "u_long rmx_expire" ;
254 .Xc
255 The time
256 (a la
257 .Xr time 3 )
258 at which this route should expire, or zero if it should never expire.
259 It is the responsibility of individual protocol suites to ensure that routes
260 are actually deleted once they expire.
261 .It Xo
262 .Vt "u_long rmx_recvpipe" ;
263 .Xc
264 Nominally, the bandwidth-delay product for the path
265 .Em from
266 the destination
267 .Em to
268 this system. In practice, this value is used to set the size of the
269 receive buffer (and thus the window in sliding-window protocols like
270 .Tn TCP ) .
271 .It Xo
272 .Vt "u_long rmx_sendpipe" ;
273 .Xc
274 As before, but in the opposite direction.
275 .It Xo
276 .Vt "u_long rmx_ssthresh" ;
277 .Xc
278 The slow-start threshold used in
279 .Tn TCP
280 congestion-avoidance.
281 .It Xo
282 .Vt "u_long rmx_rtt" ;
283 .Xc
284 The round-trip time to this destination, in units of
285 .Dv RTM_RTTUNIT
286 per second.
287 .It Xo
288 .Vt "u_long rmx_rttvar" ;
289 .Xc
290 The average deviation of the round-type time to this destination, in
291 units of
292 .Dv RTM_RTTUNIT
293 per second.
294 .It Xo
295 .Vt "u_long rmx_pksent" ;
296 .Xc
297 A count of packets successfully sent via this route.
298 .It Xo
299 .Vt "u_long rmx_filler[4]" ;
300 .Xc
301 .\" XXX badly named
302 Empty space available for protocol-specific information.
303 .El
304 .Sh SEE ALSO
305 .Xr route 4 ,
306 .Xr route 8 ,
307 .Xr rtalloc 9
308 .Sh HISTORY
309 The
310 .Nm
311 structure first appeared in
312 .Bx 4.2 .
313 The radix-tree representation of the routing table and the
314 .Nm rt_metrics
315 structure first appeared in
316 .Bx 4.3 reno .
317 The
318 .Nm RTF_PRCLONING
319 mechanism first appeared in
320 .Fx 2.0 .
321 .Sh AUTHORS
322 This manual page was written by
323 .An Garrett Wollman .
324 .Sh BUGS
325 There are a number of historical relics remaining in this interface.
326 The
327 .Li rt_gateway
328 and
329 .Li rmx_filler
330 fields could be named better.
331 .Pp
332 There is some disagreement over whether it is legitimate for
333 .Dv RTF_LLINFO
334 to be set by any process other than
335 .Fn rt_ifa->ifa_rtrequest .