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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 (Reserved for future use to indicate routes which are not to be
162 modified by a routing protocol.)
164 Indicates that the destination of this route is an address configured
165 as belonging to this system.
167 Indicates that the destination is a broadcast address.
169 Indicates that the destination is a multicast address.
172 Several metrics are supplied in
173 .Vt "struct rt_metrics"
174 passed with routing control messages via
178 .Vt rmx_mtu , rmx_expire ,
181 metrics are supplied.
182 All others are ignored.
184 The following metrics are defined by
185 .Vt "struct rt_metrics" :
186 .Bl -tag -offset indent -width 6n
187 .It Vt "u_long rmx_locks" ;
188 Flag bits indicating which metrics the kernel is not permitted to
190 .It Vt "u_long rmx_mtu" ;
192 .It Vt "u_long rmx_hopcount" ;
193 Number of intermediate systems on the path to this destination.
194 .It Vt "u_long rmx_expire" ;
198 at which this route should expire, or zero if it should never expire.
199 It is the responsibility of individual protocol suites to ensure that routes
200 are actually deleted once they expire.
201 .It Vt "u_long rmx_recvpipe" ;
202 Nominally, the bandwidth-delay product for the path
207 In practice, this value is used to set the size of the
208 receive buffer (and thus the window in sliding-window protocols like
210 .It Vt "u_long rmx_sendpipe" ;
211 As before, but in the opposite direction.
212 .It Vt "u_long rmx_ssthresh" ;
213 The slow-start threshold used in
215 congestion-avoidance.
216 .It Vt "u_long rmx_rtt" ;
217 The round-trip time to this destination, in units of
220 .It Vt "u_long rmx_rttvar" ;
221 The average deviation of the round-trip time to this destination, in
225 .It Vt "u_long rmx_pksent" ;
226 A count of packets successfully sent via this route.
227 .It Vt "u_long rmx_filler[4]" ;
229 Empty space available for protocol-specific information.
238 structure first appeared in
240 The radix-tree representation of the routing table and the
242 structure first appeared in
245 This manual page was written by
246 .An Garrett Wollman .
248 There are a number of historical relics remaining in this interface.
253 fields could be named better.