ROUTE(8) BSD System Manager's Manual ROUTE(8)
route -- manually manipulate the routing tables
route [-dnqtv] command [[modifiers] args]
The route utility is used to manually manipulate the network routing
tables. It normally is not needed, as a system routing table management
daemon, such as routed(8), should tend to this task.
The route utility supports a limited number of general options, but a
rich command language, enabling the user to specify any arbitrary request
that could be delivered via the programmatic interface discussed in
The following options are available:
-d Run in debug-only mode, i.e., do not actually modify the routing
-n Bypass attempts to print host and network names symbolically when
reporting actions. (The process of translating between symbolic
names and numerical equivalents can be quite time consuming, and
may require correct operation of the network; thus it may be
expedient to forget this, especially when attempting to repair
-v (verbose) Print additional details.
-q Suppress all output from the add, delete, and flush commands.
The route utility provides six commands:
add Add a route.
flush Remove all routes.
delete Delete a specific route.
change Change aspects of a route (such as its gateway).
get Lookup and display the route for a destination.
monitor Continuously report any changes to the routing information
base, routing lookup misses, or suspected network partition-
The monitor command has the syntax:
route [-n] monitor
The flush command has the syntax:
route [-n] flush [family]
If the flush command is specified, route will ``flush'' the routing
tables of all gateway entries. When the address family may is specified
by any of the -osi, -xns, -atalk, -inet6, or -inet modifiers, only routes
having destinations with addresses in the delineated family will be
The other commands have the following syntax:
route [-n] command [-net | -host] destination gateway [netmask]
where destination is the destination host or network, gateway is the
next-hop intermediary via which packets should be routed. Routes to a
particular host may be distinguished from those to a network by inter-
preting the Internet address specified as the destination argument. The
optional modifiers -net and -host force the destination to be interpreted
as a network or a host, respectively. Otherwise, if the destination has
a ``local address part'' of INADDR_ANY (0.0.0.0), or if the destination
is the symbolic name of a network, then the route is assumed to be to a
network; otherwise, it is presumed to be a route to a host. Optionally,
the destination could also be specified in the net/bits format.
For example, 128.32 is interpreted as -host 126.96.36.199; 128.32.130 is
interpreted as -host 188.8.131.52; -net 128.32 is interpreted as
184.108.40.206; -net 128.32.130 is interpreted as 220.127.116.11; and
192.168.64/20 is interpreted as -net 192.168.64 -netmask 255.255.240.0.
A destination of default is a synonym for -net 0.0.0.0, which is the
If the destination is directly reachable via an interface requiring no
intermediary system to act as a gateway, the -interface modifier should
be specified; the gateway given is the address of this host on the common
network, indicating the interface to be used for transmission. Alter-
nately, if the interface is point to point the name of the interface
itself may be given, in which case the route remains valid even if the
local or remote addresses change.
The optional modifiers -xns, -osi, -atalk, and -link specify that all
subsequent addresses are in the XNS, OSI, or AppleTalk address families,
or are specified as link-level addresses, and the names must be numeric
specifications rather than symbolic names.
The optional -netmask modifier is intended to achieve the effect of an
OSI ESIS redirect with the netmask option, or to manually add subnet
routes with netmasks different from that of the implied network interface
(as would otherwise be communicated using the OSPF or ISIS routing proto-
cols). One specifies an additional ensuing address parameter (to be
interpreted as a network mask). The implicit network mask generated in
the AF_INET case can be overridden by making sure this option follows the
For AF_INET6, the -prefixlen qualifier is available instead of the -mask
qualifier because non-continuous masks are not allowed in IPv6. For
example, -prefixlen 32 specifies network mask of
ffff:ffff:0000:0000:0000:0000:0000:0000 to be used. The default value of
prefixlen is 64 to get along with the aggregatable address. But 0 is
assumed if default is specified. Note that the qualifier works only for
AF_INET6 address family.
Routes have associated flags which influence operation of the protocols
when sending to destinations matched by the routes. These flags may be
set (or sometimes cleared) by indicating the following corresponding mod-
-cloning RTF_CLONING - generates a new route on use
-xresolve RTF_XRESOLVE - emit mesg on use (for external lookup)
-iface ~RTF_GATEWAY - destination is directly reachable
-static RTF_STATIC - manually added route
-nostatic ~RTF_STATIC - pretend route added by kernel or daemon
-reject RTF_REJECT - emit an ICMP unreachable when matched
-blackhole RTF_BLACKHOLE - silently discard pkts (during updates)
-proto1 RTF_PROTO1 - set protocol specific routing flag #1
-proto2 RTF_PROTO2 - set protocol specific routing flag #2
-llinfo RTF_LLINFO - validly translates proto addr to link addr
The optional modifiers -rtt, -rttvar, -sendpipe, -recvpipe, -mtu,
-hopcount, -expire, and -ssthresh provide initial values to quantities
maintained in the routing entry by transport level protocols, such as TCP
or TP4. These may be individually locked by preceding each such modifier
to be locked by the -lock meta-modifier, or one can specify that all
ensuing metrics may be locked by the -lockrest meta-modifier.
In a change or add command where the destination and gateway are not suf-
ficient to specify the route (as in the ISO case where several interfaces
may have the same address), the -ifp or -ifa modifiers may be used to
determine the interface or interface address.
The optional -proxy modifier specifies that the RTF_LLINFO routing table
entry is the ``published (proxy-only)'' ARP entry, as reported by arp(8).
The optional -genmask modifier specifies that a cloning mask is present.
This specifies the mask applied when determining if a child route should
be created. It is only applicable to network routes with the RTF_CLONING
All symbolic names specified for a destination or gateway are looked up
first as a host name using gethostbyname(3). If this lookup fails,
getnetbyname(3) is then used to interpret the name as that of a network.
The route utility uses a routing socket and the new message types
RTM_ADD, RTM_DELETE, RTM_GET, and RTM_CHANGE. As such, only the super-
user may modify the routing tables.
add [host | network ] %s: gateway %s flags %x The specified route is
being added to the tables. The values printed are from the routing table
entry supplied in the ioctl(2) call. If the gateway address used was not
the primary address of the gateway (the first one returned by
gethostbyname(3)), the gateway address is printed numerically as well as
delete [ host | network ] %s: gateway %s flags %x As above, but when
deleting an entry.
%s %s done When the flush command is specified, each routing table entry
deleted is indicated with a message of this form.
Network is unreachable 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.
not in table A delete operation was attempted for an entry which wasn't
present in the tables.
routing table overflow An add operation was attempted, but the system
was low on resources and was unable to allocate memory to create the new
gateway uses the same route A change operation resulted in a route whose
gateway uses the same route as the one being changed. The next-hop gate-
way should be reachable through a different route.
The route utility exits 0 on success, and >0 if an error occurs.
netintro(4), route(4), arp(8), IPXrouted(8), routed(8)
The route utility appeared in 4.2BSD.
The first paragraph may have slightly exaggerated routed(8)'s abilities.
Currently, routes with the RTF_BLACKHOLE flag set need to have the gate-
way set to an instance of the lo(4) driver, using the -iface option, for
the flag to have any effect; unless IP fast forwarding is enabled, in
which case the meaning of the flag will always be honored.
BSD November 4, 2004 BSD