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.\" 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 42The kernel provides a common mechanism by which all protocols can store 43and retrieve entries from a central table of routes. 44Parts of this 45mechanism are also used to interact with user-level processes by means 46of a socket in the 47.Xr route 4 48pseudo-protocol family. 49The 50.In net/route.h 51header file defines the structures and manifest constants used in this 52facility. 53.Pp 54The basic structure of a route is defined by 55.Vt "struct rtentry" , 56which includes the following fields: 57.Bl -tag -offset indent -width 6n 58.It Vt "struct radix_node rt_nodes[2]" ; 59Glue used by the radix-tree routines. 60These members also include in 61their substructure the key (i.e., destination address) and mask used 62when the route was created. 63The 64.Fn rt_key rt 65and 66.Fn rt_mask rt 67macros can be used to extract this information (in the form of a 68.Vt "struct sockaddr *" ) 69given a 70.Vt "struct rtentry *" . 71.It Vt "struct sockaddr *rt_gateway" ; 72The 73.Dq target 74of the route, which can either represent a destination in its own 75right (some protocols will put a link-layer address here), or some 76intermediate stop on the way to that destination (if the 77.Dv RTF_GATEWAY 78flag is set). 79.It Vt "u_long rt_flags" ; 80See below. 81.It Vt "struct ifnet *rt_ifp" ; 82.It Vt "struct ifaddr *rt_ifa" ; 83These two fields represent the 84.Dq answer , 85as it were, to the question posed by a route lookup; that is, they 86name the interface and interface address to be used in sending a 87packet to the destination or set of destinations which this route 88represents. 89.It Vt "struct rt_metrics_lite rt_rmx" ; 90See below. 91.It Vt "long rt_refcnt" ; 92Route entries are reference-counted; this field indicates the number 93of external (to the radix tree) references. 94If the 95.Dv RTF_UP 96flag is not present, the 97.Fn rtfree 98function will delete the route from the radix tree when the last 99reference drops. 100.It Vt "struct sockaddr *rt_genmask" ; 101When the 102.Fn rtalloc 103family of functions performs a cloning operation as requested by the 104.Dv RTF_CLONING 105flag, this field is used as the mask for the new route which is 106inserted into the table. 107If this field is a null pointer, then a host 108route is generated. 109.It Vt "caddr_t rt_llinfo" ; 110When the 111.Dv RTF_LLINFO 112flag is set, this field contains information specific to the link 113layer represented by the named interface address. 114(It is normally managed by the 115.Va rt_ifa->ifa_rtrequest 116routine.) 117Protocols such as 118.Xr arp 4 119use this field to reference per-destination state internal to that 120protocol. 121.It Vt "struct rtentry *rt_gwroute" ; 122This member is a reference to a route whose destination is 123.Va rt_gateway . 124It is only used for 125.Dv RTF_GATEWAY 126routes. 127.It Vt "struct rtentry *rt_parent" ; 128A reference to the route from which this route was cloned, or a null 129pointer if this route was not generated by cloning. 130See also the 131.Dv RTF_WASCLONED 132flag. 133.It Vt "struct mtx rt_mtx" ; 134Mutex to lock this routing entry. 135.El 136.Pp 137The following flag bits are defined: 138.Bl -tag -offset indent -width ".Dv RTF_BLACKHOLE" -compact 139.It Dv RTF_UP 140The route is not deleted. 141.It Dv RTF_GATEWAY 142The route points to an intermediate destination and not the ultimate 143recipient; the 144.Va rt_gateway 145and 146.Va rt_gwroute 147fields name that destination. 148.It Dv RTF_HOST 149This is a host route. 150.It Dv RTF_REJECT 151The destination is presently unreachable. 152This should result in an 153.Er EHOSTUNREACH 154error from output routines. 155.It Dv RTF_DYNAMIC 156This route was created dynamically by 157.Fn rtredirect . 158.It Dv RTF_MODIFIED 159This route was modified by 160.Fn rtredirect . 161.It Dv RTF_DONE 162Used only in the 163.Xr route 4 164protocol, indicating that the request was executed. 165.It Dv RTF_CLONING 166When this route is returned as a result of a lookup, automatically 167create 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 171When this route is returned as a result of a lookup, send a report on 172the 173.Xr route 4 174interface requesting that an external process perform resolution for 175this route. 176(Used in conjunction with 177.Dv RTF_CLONING . ) 178.It Dv RTF_LLINFO 179Indicates that this route represents information being managed by a 180link layer's adaptation layer (e.g., 181.Tn ARP ) . 182.It Dv RTF_STATIC 183Indicates that this route was manually added by means of the 184.Xr route 8 185command. 186.It Dv RTF_BLACKHOLE 187Requests that output sent via this route be discarded. 188.It Dv RTF_PROTO1 189.It Dv RTF_PROTO2 190.It Dv RTF_PROTO3 191Protocol-specific. 192.It Dv RTF_PRCLONING 193This flag is obsolete and simply ignored by facility. 194.It Dv RTF_WASCLONED 195Indicates that this route was generated as a result of cloning 196requested by the 197.Dv RTF_CLONING 198flag. 199When set, the 200.Va rt_parent 201field 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 204modified by a routing protocol.) 205.It Dv RTF_LOCAL 206Indicates that the destination of this route is an address configured 207as belonging to this system. 208.It Dv RTF_BROADCAST 209Indicates that the destination is a broadcast address. 210.It Dv RTF_MULTICAST 211Indicates that the destination is a multicast address. 212.El 213.Pp 214Every route has associated with it a set of metrics, stored in 215.Vt "struct rt_metrics_lite" . 216Metrics are supplied in 217.Vt "struct rt_metrics" 218passed with routing control messages via 219.Xr route 4 220API. 221Currently only 222.Vt rmx_mtu , rmx_expire , 223and 224.Vt rmx_pksent 225metrics are used in 226.Vt "struct rt_metrics_lite" . 227All others are ignored. 228.Pp 229The following metrics are defined by 230.Vt "struct rt_metrics" : 231.Bl -tag -offset indent -width 6n 232.It Vt "u_long rmx_locks" ; 233Flag bits indicating which metrics the kernel is not permitted to 234dynamically modify. 235.It Vt "u_long rmx_mtu" ; 236MTU for this path. 237.It Vt "u_long rmx_hopcount" ; 238Number of intermediate systems on the path to this destination. 239.It Vt "u_long rmx_expire" ; 240The time 241(a la 242.Xr time 3 ) 243at which this route should expire, or zero if it should never expire. 244It is the responsibility of individual protocol suites to ensure that routes 245are actually deleted once they expire. 246.It Vt "u_long rmx_recvpipe" ; 247Nominally, the bandwidth-delay product for the path 248.Em from 249the destination 250.Em to 251this system. 252In practice, this value is used to set the size of the 253receive buffer (and thus the window in sliding-window protocols like 254.Tn TCP ) . 255.It Vt "u_long rmx_sendpipe" ; 256As before, but in the opposite direction. 257.It Vt "u_long rmx_ssthresh" ; 258The slow-start threshold used in 259.Tn TCP 260congestion-avoidance. 261.It Vt "u_long rmx_rtt" ; 262The round-trip time to this destination, in units of 263.Dv RMX_RTTUNIT 264per second. 265.It Vt "u_long rmx_rttvar" ; 266The average deviation of the round-trip time to this destination, in 267units of 268.Dv RMX_RTTUNIT 269per second. 270.It Vt "u_long rmx_pksent" ; 271A count of packets successfully sent via this route. 272.It Vt "u_long rmx_filler[4]" ; 273.\" XXX badly named 274Empty 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 281The 282.Vt rtentry 283structure first appeared in 284.Bx 4.2 . 285The radix-tree representation of the routing table and the 286.Vt rt_metrics 287structure first appeared in 288.Bx 4.3 reno . 289.Sh AUTHORS 290This manual page was written by 291.An Garrett Wollman . 292.Sh BUGS 293There are a number of historical relics remaining in this interface. 294The 295.Va rt_gateway 296and 297.Va rmx_filler 298fields could be named better. 299.Pp 300There is some disagreement over whether it is legitimate for 301.Dv RTF_LLINFO 302to be set by any process other than 303.Va rt_ifa->ifa_rtrequest . 304