Manual Pages  — ROUTE

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).

The following options are available:

-4
	Specify inet address family as family hint for subcommands.
-6
	Specify inet6 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 operations).
-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.
-j jail
	Run inside a jail.

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 -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 modifiers. When a -fib option is specified, the operation will be applied to the specified FIB (routing table).

The add command has the following syntax:

route [-n] add [-net amp;| -host] destination gateway [netmask] [-fib number]

and the other commands have the following syntax:

route [-n] command [-net amp;| -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 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 -host128.0.0.32; 128.32.130 is interpreted as -host128.32.0.130; -net128.32 is interpreted as 128.32.0.0; -net128.32.130 is interpreted as 128.32.130.0; and 192.168.64/20 is interpreted as -net192.168.64 -netmask255.255.240.0.

A destination of default is a synonym for the default route. For IPv4 it is -net -inet0.0.0.0, 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 transmission. 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 change.

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 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.

For AF_INET6, the -prefixlen qualifier is available instead of the -mask qualifier because non-continuous masks are not allowed in IPv6. For example, -prefixlen32 specifies that a network mask of ffff:ffff:0000:0000:0000:0000:0000:0000 will be used. The default prefixlen is 64. However, it is assumed to be 0 if default is specified for destination. 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 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 (seetime(3)). When the first character of the number is "+" or "-", it is interpreted 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 modifier 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 "-fib2,4,6" means the FIB number 2, 4, and 6. The "-fib1,3-5,6" means the 1, 3, 4, 5, and 6.

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.

FreeBSD provides support for scalable multipath routing. It is activated by default, but can be turned off by setting the net.route.multipath sysctl(8) MIB to 0.

There are multiple route lookup algorithms available. They can be configured by setting net.route.algo.inet.algo for IPv4 and net.route.algo.inet6.algo for IPv6 sysctl(8) MIBs.

A list of available algorithms can be obtained by accessing the following sysctl(8) MIBs net.route.algo.inet.algo_list for IPv4 and net.route.algo.inet6.algo_list for IPv6.

The following algorithms are available:

radix	Base system radix backend.
bsearch	Lockless binary search in a special IP array, tailored for a small FIB with <16 routes. This algorithm is only available for IPv4.
radix_lockless
	Lockless immutable radix, re-created on every rtable change, tailored for a small FIB with <1000 routes.
dpdk_lpm	DPDK DIR24-8-based lookups, lockless datastructure, optimized for large FIBs. DIR24-8 relies on a large flat lookup table (64 MB with IPv4) which is directly indexed by the more significant portion of the lookup key. In order to use the dpdk_lpm algorithm one or both of the following kernel modules must be loaded via loader.conf(5):

dpdk_lpm4.ko
	DPDK implementation for IPv4.
dpdk_lpm6.ko
	DPDK implementation for IPv6.

dxr	IPv4 only, lockless, compressed lookup structure (below 2.5 Bytes per IPv4 prefix for large BGP FIBs) which easily fits into modern CPU cache hierarchies, lookup throughput scales linearly with CPU cores. Loadable as a kernel module at runtime or via loader.conf(5):

fib_dxr.ko

The algorithms are selected automatically based on the size of the routing table of the system. They can be changed, but not every algorithm performs best for every FIB size.

The routing table can be listed with netstat(1).

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 honored.