route(1M)

NAME

route — manually manipulate the routing tables

SYNOPSIS

/usr/sbin/route [-f] [-n] [-p pmtu] add [net|host] destination [netmask mask] gateway [count] [source src]

/usr/sbin/route inet6 [-f] [-n] [-p pmtu] add [net|host] v6destination [ / prefix] v6gateway [count] [source v6src]

/usr/sbin/route [-f] [-n] delete [net|host] destination [netmask mask] gateway [count] [source src]

/usr/sbin/route inet6 [-f] [-n] delete [net|host] v6destination [ / prefix] v6gateway [count] [source v6src]

/usr/sbin/route -f [-n]

/usr/sbin/route inet6 -f [-n]

DESCRIPTION

The route command manipulates the network routing tables manually. You must have appropriate privileges.

Subcommands

The following subcommands are supported.

add: Add the specified host or network route to the network routing table. If the route already exists, a message is printed and nothing changes.
delete: Delete the specified host or network route from the network routing table.

Options and Arguments

route recognizes the following options and arguments.

inet6

Specifies an IPv6 route. When this option is used, the destination and the gateway must have IPv6 addresses. When this option is not used, the command defaults to an IPv4 route and the destination and the gateway must have IPv4 addresses.

-f

Deletes all route table entries added through route command or through an ioctl. If this is used with one of the subcommands, the entries are deleted before the subcommand is processed.

-n

Print any host and network addresses in Internet "dot" notation for IPv4 and in "colon" notation for IPv6, except for the default network address, which is printed as default.

-p pmtu

Specifies a path maximum transmission unit (MTU) value for a static route. The minimum value allowed is 68 bytes for IPv4 and 1280 bytes for IPv6; the maximum is the MTU of the outgoing interface for this route. This option can be applied to both host and network routes.

net

or

host

The type of destination address. If this argument is omitted, routes to a particular host are distinguished from those to a network by interpreting the Internet address associated with destination. For IPv4, if the destination has a local address part of INADDR_ANY(0), the route is assumed to be to a network; otherwise, it is treated as a route to a host. For IPv6, if the destination has an address that is less than 128 bits, including any leading and trailing 0's, the route is assumed to be a network; otherwise, it is treated as a route to a host. An exception is the IPv6 "Unspecified Address", typically represented as ::, which is always interpreted as the default network route.

destination

(inet only) The destination host system where the packets will be routed. destination can be one of the following:

A host name (the official name or an alias, see gethostent(3N)).
A network name (the official name or an alias, see getnetent(3N)).
An Internet address in "dot" notation (see inet(3N)).
The keyword default, which signifies the wildcard gateway route (see routing(7)).

v6destination

(inet6 only) The destination host system where the packets will be routed. v6destination can be one of the following:

A host name (the official name or an alias, see getaddrinfo(3N)).
An IPv6 address in "colon" notation (see inet6(3N)).
The keyword default, which signifies the wildcard gateway route.

prefix

(inet6 only) The prefix is an integer between 0 and 128 inclusive. It specifies how many of the leftmost contiguous bits of the v6destination address comprise the prefix. Its format is similar to the CIDR notation in IPv4. A prefix of 0 would be a default route. If the prefix is omitted when adding a network route, then the prefix would be 64 by default. It is advisable to specify the prefix when an IPv6 network route is added. The prefix option can be applied to network routes only.

netmask mask

(inet only) The mask that will be bit-wise ANDed with destination to yield a net address where the packets will be routed. mask can be specified as a single hexadecimal number with a leading 0x, with a "dot-notation" Internet address, or with a pseudo-network name listed in the network table (see networks(4)). The length of the mask, which is the number of contiguous 1's starting from the left-most bit position of the 32-bit field, can be shorter than the default network mask for the destination address. (See routing(7)). If the netmask option is not given, mask for the route will be derived from the netmasks associated with the local interfaces. (See ifconfig(1M)). mask will be defaulted to the longest netmask of those local interfaces that have the same network address. If there is not any local interface that has the same network address, then mask will default to the default value of network mask of destination.

gateway

(inet only) The gateway through which the destination is reached. gateway can be one of the following:

A host name (the official name or an alias, see gethostent(3N)).
An Internet address in "dot" notation (see inet(3N)).

v6gateway

(inet6 only) The gateway through which the destination is reached. v6gateway can be one of the following:

A host name (the official name or an alias, see getaddrinfo(3N)).
An IPv6 address in "colon" notation (see inet6(3N)).

count

An integer that indicates whether the gateway is a remote host or the local host. If the route leads to a destination through a remote gateway, count should be a number greater than 0. If the route leads to destination and the gateway is the local host, count should be 0. The default for count is zero. The result is not defined if count is negative.

source src

(inet only) The specified source address. src can be one of the following:

A host name (the official name or an alias, see gethostent(3N)).
An Internet address in "dot" notation (see inet(3N)).

source v6src

(inet6 only) The specified source address. v6src can be one of the following:

A host name (the official name or an alias, see getaddrinfo(3N)).
An IPv6 address in "colon" notation (see inet6(3N)).

Operation

All symbolic names specified for a destination or gateway are looked up first as a host name using gethostbyname() for IPv4 and getaddrinfo() for IPv6; if the host name is not found, the destination is searched for as a network name using getnetbyname() for IPv4 only. destination and gateway can be in "dot" notation (see inet(3N)). v6destination and v6gateway can be in "colon" notation (see inet6(3N)).

If the -n option is not specified, any host and network addresses are displayed symbolically according to the name returned by gethostbyaddr() and getnetbyaddr(), respectively, except for the default network address (printed as default) and addresses that have unknown names. Addresses with unknown names are printed in Internet "dot" notation (see inet(3N)).

If the -n option is specified, any host and network addresses are printed in Internet "dot" notation except for the default network address which is printed as default.

If the -f option is specified, route deletes all route table entries that specify a remote host for a gateway. If it is used with one of the subcommands described above, the entries are deleted before the subcommand is processed.

Path MTU Discovery is a technique for discovering the maximum size of an IP datagram that can be sent on an internet path without causing datagram fragmentation in the intermediate routers. In essence, a source host that utilizes this technique initially sends out datagrams up to the the size of the outgoing interface. The Don't Fragment (DF) bit in the IP datagram header is set. As an intermediate router that supports Path MTU Discovery receives a datagram that is too large to be forwarded in one piece to the next-hop router and the DF bit is set, the router will discard the datagram and send an ICMP Destination Unreachable message with a code meaning "fragmentation needed and DF set". The ICMP message will also contain the MTU of the next-hop router. When the source host receives the ICMP message, it reduces the path MTU of the route to the MTU in the ICMP message. With this technique, the host route in the source host for this path will contain the proper MTU.

The -p pmtu option is useful only if you know the network environment well enough to enter an appropriate pmtu for a host or network route. IP will fragment a datagram to the pmtu specified for the route on the local host before sending the datagram out to the remote. It will avoid fragmentation by routers along the path, if the pmtu specified in the route command is correct.

ping can be used to find the pmtu information for the route to a remote host. The pmtu information in the routing table can be displayed with the netstat -r command (see netstat(1)).

The loopback interface (lo0) is automatically configured when the system boots with the TCP/IP software. For IPv4, the default IP address and netmask of the loopback interface are 127.0.0.1 and 255.0.0.0, respectively. For IPv6, the default IP address and prefix of the loopback interface are ::1 and 128, respectively.

When lo0 is configured, the 127.0.0.0 loopback route for IPv4 and the ::1 loopback route for IPv6 are set up automatically so that packets for any 127.*.*.* address and ::1 will loop back to the local host. Users cannot add or delete any 127.*.*.* or ::1 loopback routes.

IPv6 Operation

The keyword inet6 is required for adding or deleting IPv6 routes.

Examples

route inet6 add 2345::1 4444::3 

route inet6 add net 2222::/64 4567::8 1

route inet6 delete net 2222::/64 4567::8 1

Output

add destination: gateway gateway

The specified route is being added to the tables.

delete destination: gateway gateway

The specified route is being deleted from the tables.

Flags

The values of the count and destination type fields in the route command determine the presence of the G and H flags in the netstat -r display and thus the route type, as shown in the following table.

Count	Destination Type	Flags	Route Type
=0	network	`U`	Route to a network directly from the local host
>0	network	`UG`	Route to a network through a remote host gateway
=0	host	`UH`	Route to a remote host directly from the local host
>0	host	`UGH`	Route to a remote host through a remote host gateway
=0	`default`	`U`	Wildcard route directly from the local host
>0	`default`	`UG`	Wildcard route through a remote host gateway

DIAGNOSTICS

The following error diagnostics can be displayed:

add a route that already exists 

The specified entry is already in the routing table.

delete a route that does not exist 

The specified route was not in the routing table.

cannot update loopback route 

Routes for any 127.*.*.* loopback destination cannot be added or deleted.

WARNINGS

Reciprocal route commands must be executed on the local host, the destination host, and all intermediate hosts if routing is to succeed in the cases of virtual circuit connections or bidirectional datagram transfers.

The HP-UX implementation of route does not presently support a change subcommand.

AUTHOR

route was developed by the University of California, Berkeley.

FILES

/etc/networks
/etc/hosts