1.\" 2.\" Copyright 1996 Massachusetts Institute of Technology 3.\" 4.\" Permission to use, copy, modify, and distribute this software and 5.\" its documentation for any purpose and without fee is hereby 6.\" granted, provided that both the above copyright notice and this 7.\" permission notice appear in all copies, that both the above 8.\" copyright notice and this permission notice appear in all 9.\" supporting documentation, and that the name of M.I.T. not be used 10.\" in advertising or publicity pertaining to distribution of the 11.\" software without specific, written prior permission. M.I.T. makes 12.\" no representations about the suitability of this software for any 13.\" purpose. It is provided "as is" without express or implied 14.\" warranty. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS 17.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE, 18.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 19.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT 20.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF 23.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 24.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 25.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 26.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27.\" SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 30.Dd October 8, 1996 31.Os 32.Dt RTENTRY 9 33.Sh NAME 34.Nm rtentry 35.Nd structure of an entry in the kernel routing table 36.Sh SYNOPSIS 37.In sys/types.h 38.In sys/socket.h 39.In net/route.h 40.Sh DESCRIPTION 41The kernel provides a common mechanism by which all protocols can store 42and retrieve entries from a central table of routes. 43Parts of this 44mechanism are also used to interact with user-level processes by means 45of a socket in the 46.Xr route 4 47pseudo-protocol family. 48The 49.In net/route.h 50header file defines the structures and manifest constants used in this 51facility. 52.Pp 53The basic structure of a route is defined by 54.Dq Li struct rtentry , 55which includes the following fields: 56.Bl -tag -offset indent -width 6n 57.It Xo 58.Vt "struct radix_node rt_nodes[2]" ; 59.Xc 60Glue used by the radix-tree routines. 61These members also include in 62their substructure the key (i.e., destination address) and mask used 63when the route was created. 64The 65.Vt rt_key \&rt 66and 67.Vt rt_mask \&rt 68macros can be used to extract this information (in the form of a 69.Dq Li "struct sockaddr *" ) 70given a 71.Li "struct rtentry *" . 72.It Xo 73.Vt "struct sockaddr *rt_gateway" ; 74.Xc 75The 76.Dq target 77of the route, which can either represent a destination in its own 78right (some protocols will put a link-layer address here), or some 79intermediate stop on the way to that destination (if the 80.Dv RTF_GATEWAY 81flag is set). 82.It Xo 83.Vt "long rt_refcnt" ; 84.Xc 85Route entries are reference-counted; this field indicates the number 86of external (to the radix tree) references. 87If the 88.Dv RTF_UP 89flag is not present, the 90.Fn rtfree 91function will delete the route from the radix tree when the last 92reference drops. 93.It Xo 94.Vt "u_long rt_flags" ; 95.Xc 96See below. 97.It Xo 98.Vt "struct ifnet *rt_ifp" ; 99.Xc 100.It Xo 101.Vt "struct ifaddr *rt_ifa" ; 102.Xc 103These two fields represent the 104.Dq answer , 105as it were, to the question posed by a route lookup; that is, they 106name the interface and interface address to be used in sending a 107packet to the destination or set of destinations which this route 108represents. 109.It Xo 110.Vt "struct sockaddr *rt_genmask" ; 111.Xc 112When the 113.Fn rtalloc 114family of functions performs a cloning operation as requested by the 115.Dv RTF_CLONING 116or 117.Dv RTF_PRCLONING 118flag, this field is used as the mask for the new route which is 119inserted into the table. 120If this field is a null pointer, then a host 121route is generated. 122.It Xo 123.Vt "caddr_t rt_llinfo" ; 124.Xc 125When the 126.Dv RTF_LLINFO 127flag is set, this field contains information specific to the link 128layer represented by the named interface address. 129.Po 130It is normally managed by the 131.Vt rt_ifa->ifa_rtrequest 132routine. 133.Pc 134Protocols such as 135.Xr arp 4 136use this field to reference per-destination state internal to that 137protocol. 138.It Xo 139.Vt "struct rt_metrics rt_rmx" ; 140.Xc 141See below. 142.It Xo 143.Vt "struct rtentry *rt_gwroute" ; 144.Xc 145This member is a reference to a route whose destination is 146.Li rt_gateway . 147It is only used for 148.Dv RTF_GATEWAY 149routes. 150.\" .It Dv "int (*rt_output)();" 151.\" See below. 152.It Xo 153.Vt "struct rtentry *rt_parent" ; 154.Xc 155A reference to the route from which this route was cloned, or a null 156pointer if this route was not generated by cloning. 157See also the 158.Dv RTF_WASCLONED 159flag. 160.El 161.Pp 162The following flag bits are defined: 163.Bl -tag -offset indent -width RTF_CHAINDELETE -compact 164.It Dv RTF_UP 165The route is not deleted. 166.It Dv RTF_GATEWAY 167The route points to an intermediate destination and not the ultimate 168recipient; the 169.Li rt_gateway 170and 171.Li rt_gwroute 172fields name that destination. 173.It Dv RTF_HOST 174This is a host route. 175.It Dv RTF_REJECT 176The destination is presently unreachable. 177This should result in an 178.Er EHOSTUNREACH 179error from output routines. 180.It Dv RTF_DYNAMIC 181This route was created dynamically by 182.Fn rtredirect . 183.It Dv RTF_MODIFIED 184This route was modified by 185.Fn rtredirect . 186.It Dv RTF_DONE 187Used only in the 188.Xr route 4 189protocol, indicating that the request was executed. 190.It Dv RTF_CLONING 191When this route is returned as a result of a lookup, automatically 192create a new route using this one as a template and 193.Li rt_genmask 194(if present) as a mask. 195.It Dv RTF_XRESOLVE 196When this route is returned as a result of a lookup, send a report on 197the 198.Xr route 4 199interface requesting that an external process perform resolution for 200this route. 201.Po 202Used in conjunction with 203.Dv RTF_CLONING . 204.Pc 205.It Dv RTF_LLINFO 206Indicates that this route represents information being managed by a 207link layer's adaptation layer (e.g., 208.Tn ARP ) . 209.It Dv RTF_STATIC 210Indicates that this route was manually added by means of the 211.Xr route 8 212command. 213.It Dv RTF_BLACKHOLE 214Requests that output sent via this route be discarded. 215.It Dv RTF_PROTO1 216.It Dv RTF_PROTO2 217.It Dv RTF_PROTO3 218Protocol-specific. 219.It Dv RTF_PRCLONING 220Like 221.Dv RTF_CLONING , 222only managed by an entire protocol. 223.Po 224E.g., 225.Tn IP 226uses this flag to manage a per-host cache integrated with the routing 227table, for those destinations which do not have a link layer 228performing this function. 229.Pc 230.It Dv RTF_WASCLONED 231Indicates that this route was generated as a result of cloning 232requested by the 233.Dv RTF_CLONING 234or 235.Dv RTF_PRCLONING 236flag. 237When set, the 238.Li rt_parent 239field indicates the route from which this one was generated. 240.It Dv RTF_PINNED 241(Reserved for future use to indicate routes which are not to be 242modified by a routing protocol.) 243.It Dv RTF_LOCAL 244Indicates that the destination of this route is an address configured 245as belonging to this system. 246.It Dv RTF_BROADCAST 247Indicates that the destination is a broadcast address. 248.It Dv RTF_MULTICAST 249Indicates that the destination is a multicast address. 250.El 251.Pp 252Every route has associated with it a set of metrics, defined by 253.Li struct rt_metrics : 254.Bl -tag -offset indent -width 6n 255.It Xo 256.Vt "u_long rmx_locks" ; 257.Xc 258Flag bits indicating which metrics the kernel is not permitted to 259dynamically modify. 260.It Xo 261.Vt "u_long rmx_mtu" ; 262.Xc 263MTU for this path. 264.It Xo 265.Vt "u_long rmx_hopcount" ; 266.Xc 267Number of intermediate systems on the path to this destination. 268.It Xo 269.Vt "u_long rmx_expire" ; 270.Xc 271The time 272(a la 273.Xr time 3 ) 274at which this route should expire, or zero if it should never expire. 275It is the responsibility of individual protocol suites to ensure that routes 276are actually deleted once they expire. 277.It Xo 278.Vt "u_long rmx_recvpipe" ; 279.Xc 280Nominally, the bandwidth-delay product for the path 281.Em from 282the destination 283.Em to 284this system. 285In practice, this value is used to set the size of the 286receive buffer (and thus the window in sliding-window protocols like 287.Tn TCP ) . 288.It Xo 289.Vt "u_long rmx_sendpipe" ; 290.Xc 291As before, but in the opposite direction. 292.It Xo 293.Vt "u_long rmx_ssthresh" ; 294.Xc 295The slow-start threshold used in 296.Tn TCP 297congestion-avoidance. 298.It Xo 299.Vt "u_long rmx_rtt" ; 300.Xc 301The round-trip time to this destination, in units of 302.Dv RMX_RTTUNIT 303per second. 304.It Xo 305.Vt "u_long rmx_rttvar" ; 306.Xc 307The average deviation of the round-type time to this destination, in 308units of 309.Dv RMX_RTTUNIT 310per second. 311.It Xo 312.Vt "u_long rmx_pksent" ; 313.Xc 314A count of packets successfully sent via this route. 315.It Xo 316.Vt "u_long rmx_filler[4]" ; 317.Xc 318.\" XXX badly named 319Empty space available for protocol-specific information. 320.El 321.Sh SEE ALSO 322.Xr route 4 , 323.Xr route 8 , 324.Xr rtalloc 9 325.Sh HISTORY 326The 327.Nm 328structure first appeared in 329.Bx 4.2 . 330The radix-tree representation of the routing table and the 331.Nm rt_metrics 332structure first appeared in 333.Bx 4.3 reno . 334The 335.Nm RTF_PRCLONING 336mechanism first appeared in 337.Fx 2.0 . 338.Sh BUGS 339There are a number of historical relics remaining in this interface. 340The 341.Li rt_gateway 342and 343.Li rmx_filler 344fields could be named better. 345.Pp 346There is some disagreement over whether it is legitimate for 347.Dv RTF_LLINFO 348to be set by any process other than 349.Vt rt_ifa->ifa_rtrequest . 350.Sh AUTHORS 351This manual page was written by 352.An Garrett Wollman . 353