ROUTE(8)

NAME
route - manually manipulate the routing tables

SYNOPSIS
route [-fnqSsv] command [ [modifiers] args]

DESCRIPTION
route is a utility used to manually manipulate the network routing tables. Except for setting up the default route, it is normally not needed, as a system routing table management daemon such as routed(8), should tend to this task.

route can be used to modify nearly any aspect of the routing policy, except packet forwarding, which can be manipulated through the sysctl(8) command.

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 route(4).

-f  Remove all routes (as per flush). If used in conjunction with the add, change, delete or get commands, route removes the routes before performing the command.

-n  Bypasses 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 forgo this, especially when attempting to repair networking operations).

-q  Suppress all output from commands that manipulate the routing table.

-S  Print a space when a flag is missing so that flags are vertically aligned instead of printing the flags that are set as a contiguous string.

-s  (short) Suppresses all output from a get command except for the actual gateway that will be used. How the gateway is printed depends on the type of route being looked up.

-v  (verbose) Print additional details.

The route utility provides several commands:

add Add a route.
flush
    Remove all routes.
flushall
    Remove all routes including the default gateway.
delete
    Delete a specific route.
change
    Change aspects of a route (such as its gateway).
get Lookup and display the route for a destination.
show
    Print out the route table similar to "netstat -r" (see netstat(1)).
monitor
    Continuously report any changes to the routing information base, routing lookup misses, or suspected network partitionings.

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 is specified by any of the -xns, -atalk, -inet, -inet6, or -mpls modifiers, only routes having destinations with addresses in the delineated family will be manipulated.

The other commands have the following syntax:

route [-n] command [-net | -host] destination gateway

where destination is the destination host or network, and 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 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, 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 can also be specified in the net/bits format.

For example, 128.32 is interpreted as -host 128.0.0.32; 128.32.130 is interpreted as -host 128.32.0.130; -net 128.32 is interpreted as 128.32.0.0; and -net 128.32.130 is interpreted as 128.32.130.0.

The keyword default can be used as the destination to set up a default route to a smart gateway. If no other routes match, this default route will be used as a last resort.

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.

The optional modifiers -xns, -atalk, and -link specify that all subsequent addresses are in the XNS, or AppleTalk address families, or are specified as link-level addresses in the form described in link_addr(3), and the names must be numeric specifications rather than symbolic names.

The optional modifier -tag specifies an address associated with the route. How the address is used is specific to the address family of the destination and the interface used to forward the packet. Currently route tags are consumed only by the mpls(4) stack; therefore route assumes that the subsequent addresses are in the MPLS address family. See mpls(4) for examples of setting routes involving MPLS.

The optional -netmask qualifier is intended to achieve the effect of an 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 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 destination parameter. -prefixlen is also available for similar purpose, in IPv4 and IPv6 case.

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 modifiers:

    -cloning      RTF_CLONING    - generates a new route on use
    -nocloning   ~RTF_CLONING    - stop generating new routes on use
    -cloned       RTF_CLONED     - cloned route generated by RTF_CLONING
    -nocloned    ~RTF_CLONED     - prevent removal with RTF_CLONING parent
    -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
    -noreject    ~RTF_REJECT     - clear reject flag
    -blackhole    RTF_BLACKHOLE  - silently discard pkts (during updates)
    -noblackhole ~RTF_BLACKHOLE  - clear blackhole flag
    -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
    -proxy        RTF_ANNOUNCE   - make entry a link level proxy

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 sufficient to specify the route 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.

route 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.

EXIT STATUS
The route utility exits 0 on success, and 0 if an error occurs. This includes the use of the get command to look up a route that is incomplete.

EXAMPLES
This sets the default route to 192.168.0.1:
    route add default 192.168.0.1
This shows all routes, without DNS resolution (this is useful if the DNS is not available):
    route -n show
To install a static route through 10.200.0.1 to reach the network 192.168.1.0/28, use this:
    route add -net 192.168.1.0 -netmask 255.255.255.240 10.200.0.1

DIAGNOSTICS

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 symbolically.

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 entry.

Permission denied
    The attempted operation is privileged. Only root may modify the routing tables. These privileges are enforced by the kernel.

SEE ALSO
mpls(4), netintro(4), route(4), routed(8), sysctl(8)

HISTORY
The route command appeared in 4.2BSD. IPv6 support was added by WIDE/KAME project.

BUGS
The first paragraph may have slightly exaggerated routed(8)'s abilities.

Some uses of the -ifa or -ifp modifiers with the add command will incorrectly fail with a “Network is unreachable” message if there is no default route. See case RTM_ADD in sys/net/rtsock.c:route_output for details.