Commands Reference, Volume 4

route Command

Purpose

Manually manipulates the routing tables.

Syntax

route [ -f ] [ -n ] [ -q ] [ -v ] Command [ Family ] [ [ -net | -host ] Destination [ -prefixlen n] [ -netmask [ Address ] ] Gateway ] [ Arguments ]

Description

The route command allows you to make manual entries into the network routing tables. The route command distinguishes between routes to hosts and routes to networks by interpreting the network address of the Destination variable, which can be specified either by symbolic name or numeric address. The route command resolves all symbolic names into addresses, using either the /etc/hosts file or the network name server.

Routes to a particular host are distinguished from those to a network by interpreting the Internet address associated with the destination. The optional keywords -net and -host force the destination to be interpreted as a network or a host, respectively. 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.

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.

If the route is by way of an interface rather than through a gateway, the -interface argument should be specified. The specified gateway is the address of the host on the common network, indicating the interface to be used for transmission.

The -netmask argument must be followed by an address parameter (to be interpreted as a network mask). One can override the implicit network mask generated in the -inet case by making sure this option follows the Destination parameter.

All symbolic names specified for a destination or gateway are looked up first as a host name, using the gethostbyname subroutine. If this fails, the getnetbyname subroutine is then used to interpret the name as a network name.

Note: Route uses a routing socket and the new message types RTM_ADD, RTM_DELETE, and RTM_CHANGE. As such, only the root user may modify the routing tables.

If the flush or -f command is specified, route will "flush," or clear, the routing tables of all gateway entries. One can choose to flush only those routes whose destinations are of a given address family, by specifying an optional keyword describing which address family.

The netstat -r command displays the current routing information contained in the routing tables.

Flags

-f	Purges all entries in the routing table that are not associated with network interfaces.
-n	Displays host and network names numerically, rather than symbolically, when reporting results of a flush or of any action in verbose mode.
-q	Specifies quiet mode and suppresses all output.
-v	Specifies verbose mode and prints additional details.
-net	Indicates that the Destination parameter should be interpreted as a network.
-netmask	Specifies the network mask to the destination address. Make sure this option follows the Destination parameter.
-host	Indicates that the Destination parameter should be interpreted as a host.
-prefixlen n	Specifies the length of a destination prefix (the number of bits in the netmask).

The route default is a host (a single computer on the network). When neither the -net parameter nor the -host parameter is specified, but the network portion of the address is specified, the route is assumed to be to a network. The host portion of the address is 0 (zero).

Parameters

Arguments	Specifies one or more of the following arguments. Where n is specified as a variable to an argument, the value of the n variable is a positive integer. -active_dgd Enables Active Dead Gateway Detection on the route. -cloning Clones a new route. -genmask Extracts the length of TSEL, which is used for the generation of cloned routes. -interface Manipulates interface routing entries. -rtt n Specifies round-trip time. -rttvar n Specifies round-trip time variance.
	-sendpipe n Specifies send-window size. -recvpipe n Specifies receive-window size. -allowgroup gid Specifies a group ID that is allowed to use the route. The group ID will be added to a list of allowed groups or deleted from a list of denied groups. This argument only applies to AIX 4.2.1 or later. -denygroup gid Specifies a group ID that is not allowed to use the route. The group ID will be added to a list of denied groups or deleted from a list of allowed groups. This argument only applies to AIX 4.2.1 or later. -stopsearch Stops searching if a routing table lookup matches the route, but it is not allowed to use the route due to group routing restrictions. -mtu n Specifies maximum transmission unit for this route. Will override interface mtu for TCP applications as long as it does not exceed maximum mtu for the interface. This flag has no affect on mtu for applications using UDP. -hopcount n Specifies maximum number of gateways in the route.
	-expire n Specifies expiration metrics used by routing protocol -ssthresh n Specifies outbound gateway buffer limit. -lock Specifies a meta-modifier that can individually lock a metric modifier. The -lock meta-modifier must precede each modifier to be locked. -lockrest Specifies a meta-modifier that can lock all subsequent metrics. -if ifname Specifies the interface (en0, tr0 ...) to associate with this route so that packets will be sent using this interface when this route is chosen. -xresolve Emits a message on use (for external lookup). -iface Specifies that the destination is directly reachable. -static Specifies the manually added route. -nostatic Specifies the pretend route that is added by the kernel or daemon.
	-reject Emits an ICMP unreachable when matched. -blackhole Silently discards packets during updates. -proto1 Sets protocol specific routing flag number 1. -proto2 Sets protocol specific routing flag number 2.
Command	Specifies one of six possibilities: add Adds a route. flush or -f Removes all routes. delete Deletes a specific route. change Changes aspects of a route (such as its gateway). monitor Reports any changes to the routing information base, routing lockup misses, or suspected network partitionings. get Lookup and display the route for a destination.
Family	Specifies the address family. The -inet address family is the default. The -inet6 family specifies that all subsequent addresses are in the inet6 family, and the -xns address family specifies that all subsequent addresses are in the Xerox Network System (XNS) address family.
Destination	Identifies the host or network to which you are directing the route. The Destination parameter can be specified either by symbolic name or numeric address.
Gateway	Identifies the gateway to which packets are addressed. The Gateway parameter can be specified either by symbolic name or numeric address.

Examples

The following are examples using the route command on a TCP/IP network and an XNS network, respectively:

Inet Examples

To establish a route so that a computer on one network can send a message to a computer on a different network, enter:
```
route add 192.100.201.7 192.100.13.7
```
The 192.100.201.7 address is that of the receiving computer (the Destination parameter). The 192.100.13.7 address is that of the routing computer (the Gateway parameter).
To establish a route so you can send a message to any user on a specific network, enter:
```
route add -net 192.100.201.0 192.100.13.7
```
The 192.100.201.0 address is that of the receiving network (the Destination parameter). The 192.100.13.7 address is that of the routing network (the Gateway parameter).
To establish a default gateway, enter:
```
route add 0 192.100.13.7
```
The value 0 or the default keyword for the Destination parameter means that any packets sent to destinations not previously defined and not on a directly connected network go through the default gateway. The 192.100.13.7 address is that of the gateway chosen to be the default.
To clear the host gateway table, enter:
```
route -f
```

XNS Examples

To add a route to an XNS interface, enter:
```
route add -xns 120 110:02.60.8c.2c.a4.98
```
This adds an xns route to destination network 120 through gateway 110:02.60.8c.2c.a4.98.
To flush all the gateways in an XNS interface, enter:
```
route flush -xns
```

Related Information

The netstat command.

The routed daemon.

The gethostbyname subroutine, getnetbyname subroutine.

The /etc/hosts file format.

TCP/IP Routing, Gateways, TCP/IP Addressing in AIX 5L Version 5.2 System Management Guide: Communications and Networks.

Xerox Network Systems (XNS) Overview for Programming in AIX 5L Version 5.2 Communications Programming Concepts.