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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" ;
83 flag is not present, the
85 function will delete the route from the radix tree when the last
87 .It Vt "int rt_refcnt" ;
88 Route entries are reference-counted; this field indicates the number
89 of external (to the radix tree) references.
90 .It Vt "struct ifnet *rt_ifp" ;
91 .It Vt "struct ifaddr *rt_ifa" ;
92 These two fields represent the
94 as it were, to the question posed by a route lookup; that is, they
95 name the interface and interface address to be used in sending a
96 packet to the destination or set of destinations which this route
98 .It Vt "u_long rt_mtu";
99 See description of rmx_mtu below.
100 .It Vt "u_long rt_weight";
101 See description of rmx_weight below.
102 .It Vt "u_long rt_expire";
103 See description of rmx_expire below.
104 .It Vt "counter64_t rt_pksent";
105 See description of rmx_pksent below.
106 .It Vt "struct rtentry *rt_gwroute" ;
107 This member is a reference to a route whose destination is
112 .It Vt "struct mtx rt_mtx" ;
113 Mutex to lock this routing entry.
116 The following flag bits are defined:
117 .Bl -tag -offset indent -width ".Dv RTF_BLACKHOLE" -compact
119 The route is not deleted.
121 The route points to an intermediate destination and not the ultimate
126 fields name that destination.
128 This is a host route.
130 The destination is presently unreachable.
131 This should result in an
133 error from output routines.
135 This route was created dynamically by
138 This route was modified by
143 protocol, indicating that the request was executed.
145 When this route is returned as a result of a lookup, send a report on
148 interface requesting that an external process perform resolution for
151 Indicates that this route was manually added by means of the
155 Requests that output sent via this route be discarded.
161 Indicates that this route is immutable to a routing protocol.
163 Indicates that the destination of this route is an address configured
164 as belonging to this system.
166 Indicates that the destination is a broadcast address.
168 Indicates that the destination is a multicast address.
171 Several metrics are supplied in
172 .Vt "struct rt_metrics"
173 passed with routing control messages via
177 .Vt rmx_mtu , rmx_expire ,
180 metrics are supplied.
181 All others are ignored.
183 The following metrics are defined by
184 .Vt "struct rt_metrics" :
185 .Bl -tag -offset indent -width 6n
186 .It Vt "u_long rmx_locks" ;
187 Flag bits indicating which metrics the kernel is not permitted to
189 .It Vt "u_long rmx_mtu" ;
191 .It Vt "u_long rmx_hopcount" ;
192 Number of intermediate systems on the path to this destination.
193 .It Vt "u_long rmx_expire" ;
197 at which this route should expire, or zero if it should never expire.
198 It is the responsibility of individual protocol suites to ensure that routes
199 are actually deleted once they expire.
200 .It Vt "u_long rmx_recvpipe" ;
201 Nominally, the bandwidth-delay product for the path
206 In practice, this value is used to set the size of the
207 receive buffer (and thus the window in sliding-window protocols like
209 .It Vt "u_long rmx_sendpipe" ;
210 As before, but in the opposite direction.
211 .It Vt "u_long rmx_ssthresh" ;
212 The slow-start threshold used in
214 congestion-avoidance.
215 .It Vt "u_long rmx_rtt" ;
216 The round-trip time to this destination, in units of
219 .It Vt "u_long rmx_rttvar" ;
220 The average deviation of the round-trip time to this destination, in
224 .It Vt "u_long rmx_pksent" ;
225 A count of packets successfully sent via this route.
226 .It Vt "u_long rmx_filler[4]" ;
228 Empty space available for protocol-specific information.
237 structure first appeared in
239 The radix-tree representation of the routing table and the
241 structure first appeared in
244 This manual page was written by
245 .An Garrett Wollman .
247 There are a number of historical relics remaining in this interface.
252 fields could be named better.