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
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 program-
matic interface discussed in route(4).
The following options are available:
-4 Specify inet address family as family hint for subcommands.
-6 Specify inet address family as family hint for subcommands.
-d Run in debug-only mode, i.e., do not actually modify the routing table.
-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 networking opera-
-t Run in test-only mode. /dev/null is used instead of a socket.
-v (verbose) Print additional details.
-q Suppress all output from the add, change, delete, and flush commands.
The route utility provides the following commands:
add Add a route.
flush Remove all routes.
delete Delete a specific route.
del Another name for the delete command.
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 partitionings.
show Another name for the get command.
The monitor command has the syntax:
route [-n] monitor [-fib number]
The flush command has the syntax:
route [-n flush] [family] [-fib number]
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, -inet6, or
-inet modifiers, only routes having destinations with addresses in the delineated family
will be deleted. Additionally, -4 or -6 can be used as aliases for -inet and -inet6 modi-
fiers. When a -fib option is specified, the operation will be applied to the specified FIB
The other commands have the following syntax:
route [-n] command [-net | -host] destination gateway [netmask] [-fib number]
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 interpreting the Internet address specified as the destination argu-
ment. 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 18.104.22.168; 128.32.130 is interpreted as -host
22.214.171.124; -net 128.32 is interpreted as 126.96.36.199; -net 128.32.130 is interpreted as
188.8.131.52; 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 the default route. For IPv4 it is -net -inet
0.0.0.0, and for IPv6 it is -net -inet6 ::.
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 trans-
mission. Alternately, 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
The optional modifiers -xns, -osi, and -link specify that all subsequent addresses are in
the XNS or OSI 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 protocols). One specifies an additional ensuing address parameter (to be inter-
preted as a network mask). The implicit network mask generated in the AF_INET case can be
overridden by making sure this option follows the destination parameter.
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 des-
tinations matched by the routes. These flags may be set (or sometimes cleared) by indicat-
ing the following corresponding modifiers:
-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
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.
Note that -expire accepts expiration time of the route as the number of seconds since the
Epoch (see time(3)). When the first character of the number is ``+'' or ``-'', it is inter-
preted as a value relative to the current time.
The optional modifier -fib number specifies that the command will be applied to a non-
default FIB. The number must be smaller than the net.fibs sysctl(8) MIB. When this modi-
fier is not specified, or a negative number is specified, the default FIB shown in the
net.my_fibnum sysctl(8) MIB will be used.
The number allows multiple FIBs by a comma-separeted list and/or range specification. The
"-fib 2,4,6" means the FIB number 2, 4, and 6. The "-fib 1,3-5,6" means the 1, 3, 4, 5, and
In a change or add command where the destination and gateway are not sufficient 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.
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.
The route utility exits 0 on success, and >0 if an error occurs.
Add a default route to the network routing table. This will send all packets for destina-
tions not available in the routing table to the default gateway at 192.168.1.1:
route add -net 0.0.0.0/0 192.168.1.1
A shorter version of adding a default route can also be written as:
route add default 192.168.1.1
Add a static route to the 172.16.10.0/24 network via the 172.16.1.1 gateway:
route add -net 172.16.10.0/24 172.16.1.1
Change the gateway of an already established static route in the routing table:
route change -net 172.16.10.0/24 172.16.1.2
Display the route for a destination network:
route show 172.16.10.0
Delete a static route from the routing table:
route delete -net 172.16.10.0/24 172.16.1.2
Remove all routes from the routing table:
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 symbol-
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 indi-
cated 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 was not present in the
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 entry.
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 gateway should be reachable through a
netintro(4), route(4), arp(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 gateway 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
BSD November 11, 2014 BSD