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31 .Dd October 7, 2004
32 .Os
33 .Dt RTENTRY 9
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.
44 Parts of this
45 mechanism are also used to interact with user-level processes by means
46 of a socket in the
47 .Xr route 4
48 pseudo-protocol family.
49 The
50 .In net/route.h
51 header file defines the structures and manifest constants used in this
52 facility.
53 .Pp
54 The basic structure of a route is defined by
55 .Vt "struct rtentry" ,
56 which includes the following fields:
57 .Bl -tag -offset indent -width 6n
58 .It Vt "struct radix_node rt_nodes[2]" ;
59 Glue used by the radix-tree routines.
60 These members also include in
61 their substructure the key (i.e., destination address) and mask used
62 when the route was created.
63 The
64 .Fn rt_key rt
65 and
66 .Fn rt_mask rt
67 macros can be used to extract this information (in the form of a
68 .Vt "struct sockaddr *" )
69 given a
70 .Vt "struct rtentry *" .
71 .It Vt "struct sockaddr *rt_gateway" ;
72 The
73 .Dq target
74 of the route, which can either represent a destination in its own
75 right (some protocols will put a link-layer address here), or some
76 intermediate stop on the way to that destination (if the
77 .Dv RTF_GATEWAY
78 flag is set).
79 .It Vt "u_long rt_flags" ;
80 See below.
81 .It Vt "struct ifnet *rt_ifp" ;
82 .It Vt "struct ifaddr *rt_ifa" ;
83 These two fields represent the
84 .Dq answer ,
85 as it were, to the question posed by a route lookup; that is, they
86 name the interface and interface address to be used in sending a
87 packet to the destination or set of destinations which this route
88 represents.
89 .It Vt "struct rt_metrics_lite rt_rmx" ;
90 See below.
91 .It Vt "long rt_refcnt" ;
92 Route entries are reference-counted; this field indicates the number
93 of external (to the radix tree) references.
94 If the
95 .Dv RTF_UP
96 flag is not present, the
97 .Fn rtfree
98 function will delete the route from the radix tree when the last
99 reference drops.
100 .It Vt "struct sockaddr *rt_genmask" ;
101 When the
102 .Fn rtalloc
103 family of functions performs a cloning operation as requested by the
104 .Dv RTF_CLONING
105 flag, this field is used as the mask for the new route which is
106 inserted into the table.
107 If this field is a null pointer, then a host
108 route is generated.
109 .It Vt "caddr_t rt_llinfo" ;
110 When the
111 .Dv RTF_LLINFO
112 flag is set, this field contains information specific to the link
113 layer represented by the named interface address.
114 (It is normally managed by the
115 .Va rt_ifa->ifa_rtrequest
116 routine.)
117 Protocols such as
118 .Xr arp 4
119 use this field to reference per-destination state internal to that
120 protocol.
121 .It Vt "struct rtentry *rt_gwroute" ;
122 This member is a reference to a route whose destination is
123 .Va rt_gateway .
124 It is only used for
125 .Dv RTF_GATEWAY
126 routes.
127 .It Vt "struct rtentry *rt_parent" ;
128 A reference to the route from which this route was cloned, or a null
129 pointer if this route was not generated by cloning.
130 See also the
131 .Dv RTF_WASCLONED
132 flag.
133 .It Vt "struct mtx rt_mtx" ;
134 Mutex to lock this routing entry.
135 .El
136 .Pp
137 The following flag bits are defined:
138 .Bl -tag -offset indent -width ".Dv RTF_BLACKHOLE" -compact
139 .It Dv RTF_UP
140 The route is not deleted.
141 .It Dv RTF_GATEWAY
142 The route points to an intermediate destination and not the ultimate
143 recipient; the
144 .Va rt_gateway
145 and
146 .Va rt_gwroute
147 fields name that destination.
148 .It Dv RTF_HOST
149 This is a host route.
150 .It Dv RTF_REJECT
151 The destination is presently unreachable.
152 This should result in an
153 .Er EHOSTUNREACH
154 error from output routines.
155 .It Dv RTF_DYNAMIC
156 This route was created dynamically by
157 .Fn rtredirect .
158 .It Dv RTF_MODIFIED
159 This route was modified by
160 .Fn rtredirect .
161 .It Dv RTF_DONE
162 Used only in the
163 .Xr route 4
164 protocol, indicating that the request was executed.
165 .It Dv RTF_CLONING
166 When this route is returned as a result of a lookup, automatically
167 create a new route using this one as a template and
168 .Va rt_genmask
169 (if present) as a mask.
170 .It Dv RTF_XRESOLVE
171 When this route is returned as a result of a lookup, send a report on
172 the
173 .Xr route 4
174 interface requesting that an external process perform resolution for
175 this route.
176 (Used in conjunction with
177 .Dv RTF_CLONING . )
178 .It Dv RTF_LLINFO
179 Indicates that this route represents information being managed by a
180 link layer's adaptation layer (e.g.,
181 .Tn ARP ) .
182 .It Dv RTF_STATIC
183 Indicates that this route was manually added by means of the
184 .Xr route 8
185 command.
186 .It Dv RTF_BLACKHOLE
187 Requests that output sent via this route be discarded.
188 .It Dv RTF_PROTO1
189 .It Dv RTF_PROTO2
190 .It Dv RTF_PROTO3
191 Protocol-specific.
192 .It Dv RTF_PRCLONING
193 This flag is obsolete and simply ignored by facility.
194 .It Dv RTF_WASCLONED
195 Indicates that this route was generated as a result of cloning
196 requested by the
197 .Dv RTF_CLONING
198 flag.
199 When set, the
200 .Va rt_parent
201 field indicates the route from which this one was generated.
202 .It Dv RTF_PINNED
203 (Reserved for future use to indicate routes which are not to be
204 modified by a routing protocol.)
205 .It Dv RTF_LOCAL
206 Indicates that the destination of this route is an address configured
207 as belonging to this system.
208 .It Dv RTF_BROADCAST
209 Indicates that the destination is a broadcast address.
210 .It Dv RTF_MULTICAST
211 Indicates that the destination is a multicast address.
212 .El
213 .Pp
214 Every route has associated with it a set of metrics, stored in
215 .Vt "struct rt_metrics_lite" .
216 Metrics are supplied in
217 .Vt "struct rt_metrics"
218 passed with routing control messages via
219 .Xr route 4
220 API.
221 Currently only
222 .Vt rmx_mtu , rmx_expire ,
223 and
224 .Vt rmx_pksent
225 metrics are used in
226 .Vt "struct rt_metrics_lite" .
227 All others are ignored.
228 .Pp
229 The following metrics are defined by
230 .Vt "struct rt_metrics" :
231 .Bl -tag -offset indent -width 6n
232 .It Vt "u_long rmx_locks" ;
233 Flag bits indicating which metrics the kernel is not permitted to
234 dynamically modify.
235 .It Vt "u_long rmx_mtu" ;
236 MTU for this path.
237 .It Vt "u_long rmx_hopcount" ;
238 Number of intermediate systems on the path to this destination.
239 .It Vt "u_long rmx_expire" ;
240 The time
241 (a la
242 .Xr time 3 )
243 at which this route should expire, or zero if it should never expire.
244 It is the responsibility of individual protocol suites to ensure that routes
245 are actually deleted once they expire.
246 .It Vt "u_long rmx_recvpipe" ;
247 Nominally, the bandwidth-delay product for the path
248 .Em from
249 the destination
250 .Em to
251 this system.
252 In practice, this value is used to set the size of the
253 receive buffer (and thus the window in sliding-window protocols like
254 .Tn TCP ) .
255 .It Vt "u_long rmx_sendpipe" ;
256 As before, but in the opposite direction.
257 .It Vt "u_long rmx_ssthresh" ;
258 The slow-start threshold used in
259 .Tn TCP
260 congestion-avoidance.
261 .It Vt "u_long rmx_rtt" ;
262 The round-trip time to this destination, in units of
263 .Dv RMX_RTTUNIT
264 per second.
265 .It Vt "u_long rmx_rttvar" ;
266 The average deviation of the round-trip time to this destination, in
267 units of
268 .Dv RMX_RTTUNIT
269 per second.
270 .It Vt "u_long rmx_pksent" ;
271 A count of packets successfully sent via this route.
272 .It Vt "u_long rmx_filler[4]" ;
273 .\" XXX badly named
274 Empty space available for protocol-specific information.
275 .El
276 .Sh SEE ALSO
277 .Xr route 4 ,
278 .Xr route 8 ,
279 .Xr rtalloc 9
280 .Sh HISTORY
281 The
282 .Vt rtentry
283 structure first appeared in
284 .Bx 4.2 .
285 The radix-tree representation of the routing table and the
286 .Vt rt_metrics
287 structure first appeared in
288 .Bx 4.3 reno .
289 .Sh AUTHORS
290 This manual page was written by
291 .An Garrett Wollman .
292 .Sh BUGS
293 There are a number of historical relics remaining in this interface.
294 The
295 .Va rt_gateway
296 and
297 .Va rmx_filler
298 fields could be named better.
299 .Pp
300 There is some disagreement over whether it is legitimate for
301 .Dv RTF_LLINFO
302 to be set by any process other than
303 .Va rt_ifa->ifa_rtrequest .