1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
288 lines
8.9 KiB
Groff
288 lines
8.9 KiB
Groff
.\"
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.\" Copyright 1996 Massachusetts Institute of Technology
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.\"
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.\" Permission to use, copy, modify, and distribute this software and
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.\" its documentation for any purpose and without fee is hereby
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.\" granted, provided that both the above copyright notice and this
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.\" permission notice appear in all copies, that both the above
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.\" copyright notice and this permission notice appear in all
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.\" supporting documentation, and that the name of M.I.T. not be used
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.\" in advertising or publicity pertaining to distribution of the
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.\" software without specific, written prior permission. M.I.T. makes
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.\" no representations about the suitability of this software for any
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.\" purpose. It is provided "as is" without express or implied
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.\" warranty.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
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.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
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.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
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.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.Dd October 8, 1996
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.Os
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.Dt RTENTRY 9
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.Sh NAME
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.Nm rtentry
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.Nd structure of an entry in the kernel routing table
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.Sh SYNOPSIS
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.Fd #include <sys/socket.h>
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.Fd #include <net/route.h>
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.Sh DESCRIPTION
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The kernel provides a common mechanism by which all protocols can store
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and retrieve entries from a central table of routes. Parts of this
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mechanism are also used to interact with user-level processes by means
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of a socket in the
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.Xr route 4
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pseudo-protocol family.
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The
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.Aq Pa net/route.h
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header file defines the structures and manifest constants used in this
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facility.
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.Pp
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The basic structure a route is defined by
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.Dq Li struct rtentry ,
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which includes the following fields:
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.Bl -tag -offset indent -width 6n
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.It Li "struct radix_node rt_nodes[2];"
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Glue used by the radix-tree routines. These members also include in
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their substructure the key (i.e., destination address) and mask used
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when the route was created. The
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.Fn rt_key \&rt
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and
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.Fn rt_mask \&rt
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macros can be used to extract this information (in the form of a
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.Dq Li "struct sockaddr *" )
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given a
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.Li "struct rtentry *" .
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.It Li "struct sockaddr *rt_gateway;"
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The
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.Dq target
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of the route, which can either represent a destination in its own
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right (some protocols will put a link-layer address here), or some
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intermediate stop on the way to that destination (if the
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.Dv RTF_GATEWAY
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flag is set).
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.It Li "short rt_refcnt;"
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Route entries are reference-counted; this field indicates the number
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of external (to the radix tree) references. If the
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.Dv RTF_UP
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flag is not present, the
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.Fn rtfree
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function will delete the route from the radix tree when the last
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reference drops.
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.It Li "u_long rt_flags;"
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See below.
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.It Li "struct ifnet *rt_ifp;"
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.It Li "struct ifaddr *rt_ifa;"
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These two fields represent the
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.Dq answer ,
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as it were, to the question posed by a route lookup; that is, they
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name the interface and interface address to be used in sending a
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packet to the destination or set of destinations which this route
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represents.
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.It Li "struct sockaddr *rt_genmask;"
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When the
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.Fn rtalloc
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family of functions performs a cloning operation as requested by the
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.Dv RTF_CLONING
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or
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.Dv RTF_PRCLONING
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flag, this field is used as the mask for the new route which is
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inserted into the table. If this field is a null pointer, then a host
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route is generated.
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.It Li "caddr_t rt_llinfo;"
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When the
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.Dv RTF_LLINFO
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flag is set, this field contains information specific to the link
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layer represented by the named interface address. (It is normally
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managed by the
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.Fn rt_ifa->ifa_rtrequest
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routine.) Protocols such as
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.Xr arp 4
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use this field to reference per-destination state internal to that
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protocol.
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.It Li "struct rt_metrics rt_rmx;"
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See below.
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.It Li "struct rtentry *rt_gwroute;"
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This member is a reference to a route whose destination is
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.Li rt_gateway .
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It is only used for
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.Dv RTF_GATEWAY
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routes.
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.\" .It Dv "int (*rt_output)();"
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.\" See below.
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.It Dv "struct rtentry *rt_parent;"
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A reference to the route from which this route was cloned, or a null
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pointer if this route was not generated by cloning. See also the
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.Dv RTF_WASCLONED
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flag.
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.El
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.Pp
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The following flag bits are defined:
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.Bl -tag -offset indent -width RTF_CHAINDELETE -compact
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.It Dv RTF_UP
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The route is not deleted.
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.It Dv RTF_GATEWAY
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The route points to an intermediate destination and not the ultimate
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recipient; the
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.Li rt_gateway
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and
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.Li rt_gwroute
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fields name that destination.
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.It Dv RTF_HOST
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This is a host route.
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.It Dv RTF_REJECT
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The destination is presently unreachable. This should result in an
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.Er EHOSTUNREACH
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error from output routines.
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.It Dv RTF_DYNAMIC
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This route was created dynamically by
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.Fn rtredirect .
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.It Dv RTF_MODIFIED
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This route was modified by
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.Fn rtredirect .
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.It Dv RTF_DONE
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Used only in the
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.Xr route 4
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protocol, indicating that the request was executed.
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.It Dv RTF_CLONING
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When this route is returned as a result of a lookup, automatically
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create a new route using this one as a template and
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.Li rt_genmask
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(if present) as a mask.
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.It Dv RTF_XRESOLVE
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When this route is returned as a result of a lookup, send a report on
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the
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.Xr route 4
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interface requesting that an external process perform resolution for
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this route. (Used in conjunction with
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.Dv RTF_CLONING . )
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.It Dv RTF_LLINFO
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Indicates that this route represents information being managed by a
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link layer's adaptation layer (e.g.,
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.Tn ARP ) .
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.It Dv RTF_STATIC
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Indicates that this route was manually added by means of the
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.Xr route 8
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command.
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.It Dv RTF_BLACKHOLE
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Requests that output sent via this route be discarded.
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.It Dv RTF_PROTO1
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.It Dv RTF_PROTO2
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.It Dv RTF_PROTO3
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Protocol-specific.
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.It Dv RTF_PRCLONING
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Like
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.Dv RTF_CLONING ,
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only managed by an entire protocol. (E.g.,
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.Tn IP
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uses this flag to manage a per-host cache integrated with the routing
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table, for those destinations which do not have a link layer
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performing this function.)
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.It Dv RTF_WASCLONED
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Indicates that this route was generated as a result of cloning
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requested by the
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.Dv RTF_CLONING
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or
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.Dv RTF_PRCLONING
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flag. When set, the
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.Li rt_parent
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field indicates the route from which this one was generated.
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.It Dv RTF_PINNED
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(Reserved for future use to indicate routes which are not to be
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modified by a routing protocol.)
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.It Dv RTF_LOCAL
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Indicates that the destination of this route is an address configured
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as belonging to this system.
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.It Dv RTF_BROADCAST
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Indicates that the destination is a broadcast address.
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.It Dv RTF_MULTICAST
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Indicates that the destination is a multicast address.
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.El
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.Pp
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Every route has associated with it a set of metrics, defined by
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.Li struct rt_metrics :
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.Bl -tag -offset indent -width 6n
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.It Li "u_long rmx_locks;"
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Flag bits indicating which metrics the kernel is not permitted to
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dynamically modify.
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.It Li "u_long rmx_mtu;"
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MTU for this path.
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.It Li "u_long rmx_hopcount;"
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Number of intermediate systems on the path to this destination.
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.It Li "u_long rmx_expire;"
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The time
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(\*(aga la
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.Xr time 2 )
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at which this route should expire, or zero if it should never expire.
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It is the responsibility of individual protocol suites to ensure that routes
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are actually deleted once they expire.
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.It Li "u_long rmx_recvpipe;"
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Nominally, the bandwidth-delay product for the path
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.Em from
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the destination
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.Em to
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this system. In practice, this value is used to set the size of the
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receive buffer (and thus the window in sliding-window protocols like
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.Tn TCP ) .
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.It Li "u_long rmx_sendpipe;"
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As before, but in the opposite direction.
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.It Li "u_long rmx_ssthresh;"
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The slow-start threshold used in
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.Tn TCP
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congestion-avoidance.
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.It Li "u_long rmx_rtt;"
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The round-trip time to this destination, in units of
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.Dv RMX_RTTUNIT
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per second.
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.It Li "u_long rmx_rttvar;"
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The average deviation of the round-type time to this destination, in
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units of
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.Dv RMX_RTTUNIT
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per second.
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.It Li "u_long rmx_pksent;"
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A count of packets successfully sent via this route.
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.It Li "u_long rmx_filler[4];"
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.\" XXX badly named
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Empty space available for protocol-specific information.
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.El
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.Sh SEE ALSO
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.Xr route 4 ,
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.Xr route 8 ,
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.Xr rtalloc 9
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.Sh HISTORY
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The
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.Nm rtentry
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structure first appeared in
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.Bx 4.2 .
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The radix-tree representation of the routing table and the
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.Nm rt_metrics structure first appeared in
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.Bx 4.3 reno .
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The
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.Nm RTF_PRCLONING
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mechanism first appeared in
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.Fx 2.0 .
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.Sh BUGS
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There are a number of historical relics remaining in this interface.
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The
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.Li rt_gateway
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and
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.Li rmx_filler
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fields could be named better.
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.Pp
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There is some disagreement over whether it is legitimate for
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.Dv RTF_LLINFO
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to be set by any process other than
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.Fn rt_ifa->ifa_rtrequest .
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.Sh AUTHOR
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This manual page was written by Garrett Wollman.
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