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36 .Nd structure of an entry in the kernel routing table
42 The kernel provides a common mechanism by which all protocols can store
43 and retrieve entries from a central table of routes.
45 mechanism are also used to interact with user-level processes by means
48 pseudo-protocol family.
51 header file defines the structures and manifest constants used in this
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.
67 macros can be used to extract this information (in the form of a
68 .Vt "struct sockaddr *" )
70 .Vt "struct rtentry *" .
71 .It Vt "struct sockaddr *rt_gateway" ;
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
79 .It Vt "int rt_flags" ;
81 .It Vt "int rt_refcnt" ;
82 Route entries are reference-counted; this field indicates the number
83 of external (to the radix tree) references.
84 .It Vt "struct ifnet *rt_ifp" ;
85 .It Vt "struct ifaddr *rt_ifa" ;
86 These two fields represent the
88 as it were, to the question posed by a route lookup; that is, they
89 name the interface and interface address to be used in sending a
90 packet to the destination or set of destinations which this route
92 .It Vt "struct rt_metrics_lite rt_rmx" ;
96 flag is not present, the
98 function will delete the route from the radix tree when the last
100 .It Vt "struct rtentry *rt_gwroute" ;
101 This member is a reference to a route whose destination is
106 .It Vt "struct mtx rt_mtx" ;
107 Mutex to lock this routing entry.
110 The following flag bits are defined:
111 .Bl -tag -offset indent -width ".Dv RTF_BLACKHOLE" -compact
113 The route is not deleted.
115 The route points to an intermediate destination and not the ultimate
120 fields name that destination.
122 This is a host route.
124 The destination is presently unreachable.
125 This should result in an
127 error from output routines.
129 This route was created dynamically by
132 This route was modified by
137 protocol, indicating that the request was executed.
139 When this route is returned as a result of a lookup, send a report on
142 interface requesting that an external process perform resolution for
145 Indicates that this route was manually added by means of the
149 Requests that output sent via this route be discarded.
155 This flag is obsolete and simply ignored by facility.
157 Indicates that this route is immutable to a routing protocol.
159 Indicates that the destination of this route is an address configured
160 as belonging to this system.
162 Indicates that the destination is a broadcast address.
164 Indicates that the destination is a multicast address.
167 Every route has associated with it a set of metrics, stored in
168 .Vt "struct rt_metrics_lite" .
169 Metrics are supplied in
170 .Vt "struct rt_metrics"
171 passed with routing control messages via
175 .Vt rmx_mtu , rmx_expire ,
179 .Vt "struct rt_metrics_lite" .
180 All others are ignored.
182 The following metrics are defined by
183 .Vt "struct rt_metrics" :
184 .Bl -tag -offset indent -width 6n
185 .It Vt "u_long rmx_locks" ;
186 Flag bits indicating which metrics the kernel is not permitted to
188 .It Vt "u_long rmx_mtu" ;
190 .It Vt "u_long rmx_hopcount" ;
191 Number of intermediate systems on the path to this destination.
192 .It Vt "u_long rmx_expire" ;
196 at which this route should expire, or zero if it should never expire.
197 It is the responsibility of individual protocol suites to ensure that routes
198 are actually deleted once they expire.
199 .It Vt "u_long rmx_recvpipe" ;
200 Nominally, the bandwidth-delay product for the path
205 In practice, this value is used to set the size of the
206 receive buffer (and thus the window in sliding-window protocols like
208 .It Vt "u_long rmx_sendpipe" ;
209 As before, but in the opposite direction.
210 .It Vt "u_long rmx_ssthresh" ;
211 The slow-start threshold used in
213 congestion-avoidance.
214 .It Vt "u_long rmx_rtt" ;
215 The round-trip time to this destination, in units of
218 .It Vt "u_long rmx_rttvar" ;
219 The average deviation of the round-trip time to this destination, in
223 .It Vt "u_long rmx_pksent" ;
224 A count of packets successfully sent via this route.
225 .It Vt "u_long rmx_filler[4]" ;
227 Empty space available for protocol-specific information.
236 structure first appeared in
238 The radix-tree representation of the routing table and the
240 structure first appeared in
243 This manual page was written by
244 .An Garrett Wollman .
246 There are a number of historical relics remaining in this interface.
251 fields could be named better.