route.8c

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)route.8c	8.1	9/11/90
.TH route 8c
.SH Name
route \- manually manipulate the routing tables
.SH Syntax
.B /etc/route
[
.B \-f
] [
.B \-n
] 
.I command args
]
.SH Description
.NXR "route program"
.NXA "route program" "routed program"
.NXA "routed program" "route program"
.NXR "routing table" "manipulating"
The
.PN route
program is used to manipulate the network
routing tables manually.  However, normally it is not needed, as the
system routing table management daemon, 
.MS routed 8c ,
should tend to this task.
.PP
The
.PN route
program accepts two commands:
.NXR "route program" "commands"
.IR add ,
to add a route and
.IR delete ,
to delete a route. 
.PP
All commands have the following syntax:
.PP
.ti +0.5i
.B /etc/route 
.I command
[
.B net
|
.B host
]
.I destination gateway
[
.I metric
]
.PP
In this syntax,
.I destination
is a host or network for which
the route is to,
.I gateway
is the gateway to which packets should be addressed, and
.I metric
is an optional count indicating the number of hops to
the
.IR destination .
The metric is required for 
.B add
commands.
It must be zero if the destination is on a directly-attached network,
and nonzero if the route utilizes one or more gateways.
.PP
When adding a route with metric 0, the gateway given is the address 
of this host on the common
network, indicating the interface to be used for transmission.
Routes to a particular host are distinguished from routes to
a network by interpreting the Internet address associated with
.IR destination .
The optional keywords 
.B net
and
.B host
force the destination to be interpreted 
as a network or host, respectively.
If the 
.I destination
has a local address part of INADDR_ANY, then the route is
assumed to be to a network. Otherwise, it is presumed to be a
route to a host.  If the route is to a destination connected
via a gateway, the 
.I metric
should be greater than 0.  All symbolic names specified for a
.I destination 
or 
.I gateway
are looked up first as a host name using
.MS gethostbyname 3n .
If this lookup fails, 
.MS getnetbyname 3n
is then used to interpret the name as that of a network.
.PP
The
.PN route
command uses a raw socket and the SIOCADDRT and SIOCDELRT
ioctls
to do its work.  As such, only the superuser can modify
the routing tables.
.SH Options
.IP \fB\-f\fR 5
Flushes the routing tables of all gateway entries.
If 
.PN \-f
is used with one of the commands
described above, the tables are flushed prior to the command's
application.
.IP \fB\-n\fR 5
Prevents attempts to print host and network names symbolically when reporting 
actions.
.SH Restrictions
.NXR "route program" "restricted"
The change operation is not implemented.
Therefore, you should first add the new route,
and then delete the old one.
.SH Diagnostics
.NXR "route program" "diagnostics"
.B add [host | network] %s: gateway %s flags %x"
.br
The specified route is being added to the tables.  The
values printed are from the routing table entry supplied
in the 
.I ioctl
call.  If the gateway address used was not the primary address of the
gateway (the first one returned by
.PN gethostbyname),
the gateway address is printed numerically as well as symbolically.
.PP
.B "delete [ host | network] %s: gateway %s flags %x"
.br
The specified route is being deleted from the tables.  The
values printed are from the routing table entry supplied
in the 
.I ioctl
call.  If the gateway address used was not the primary address of the
gateway (the first one returned by
.PN gethostbyname),
the gateway address is printed numerically as well as symbolically.
.PP
.B "%s %s done"
.br
When the 
.PN \-f
flag is specified, each routing table entry that is deleted
is indicated with a message of this form.
.PP
.B "Network is unreachable"
.br
An attempt to add a route failed because the gateway listed was not on a 
directly-connected network.  The next-hop gateway must be given.
.PP
.B "not in table"
.br
A delete operation was attempted for an entry which
was not present in the tables.
.PP
.B "routing table overflow"
.br
An add operation was attempted, but the system was
low on resources and was unable to allocate memory
to create the new entry.
.SH See Also
intro(4n), routed(8c)