Configuring Internet Protocol (IP) routing

gated interfaces statements

The gated interfaces statement has the following syntax:

   interfaces {
       options
           [ strictinterfaces ]
           [ scaninterval time ]
           ;
       interface interface_list
           [ preference preference ]
           [ down preference preference ]
           [ passive ]
           [ simplex ]
           ;
       define address
           [ broadcast address ] | [ pointtopoint address ]
           [ netmask mask ]
           [ multicast ]
           ;
   } ;

An interface is the connection between a router and one of its attached networks. A physical interface may be specified by interface name, by IP address, or by domain name (unless the network is an unnumbered point-to-point network). Multiple levels of reference in the configuration language allow identification of an interface using an interface name wildcard, an interface name, or an interface IP address. The interface_list is a list of one or more interface names including wildcard names (names without a number), names that may specify more than one interface or address, or the token all for all interfaces.

The statement clause options allows configuration of some global options related to interfaces. These are:

strictinterfaces: Indicates that it is a fatal error to reference an interface in the configuration file that is not present when gated is started and not listed in a define statement. Without this option, a warning message will be issued, but gated will continue.
scaninterval time: Specifies how often gated scans the kernel interface list for changes. The default is every 15 seconds on most systems, and 60 seconds on systems that pass interface status changes through the routing socket (such as BSD 4.4). Note that gated will also scan the interface list on receipt of a SIGUSR2.

The statement clause ``interface interface_list'' sets interface options on the specified interfaces. An interface list is ``all'' or a list of interface names, domain names, or numeric addresses. Options available on this clause are:

preference preference: Sets the preference for routes to this interface when it is up and appears to be functioning properly. The default preference is 0.
down preference preference: Sets the preference for routes to this interface when gated does not believe it to be functioning properly, but the kernel does not indicate it is down. The default value is 120.
passive: Prevents gated from changing the preference of the route to this interface if it is not believed to be functioning properly due to lack of received routing information. gated will only perform this check if the interface is actively participating in a routing protocol.
simplex: Defines an interface as unable to hear its own broadcast packets. Some systems define an interface as simplex with the IFF_SIMPLEX flag. On others, it needs to be specified in the configuration file. On simplex interfaces, packets from myself are assumed to have been looped back in software and are not used as an indication that the interface is functioning properly.

The statement clause ``define address'' defines interfaces that might not be present when gated is started, so they may be referenced in the configuration file when strictinterfaces is defined. Possible define keywords are:

broadcast address: Defines the interface as broadcast capable (for example Ethernet or Token-Ring) and specifies the broadcast address.
pointtopoint address: Defines the interface as a point-to-point interface such as PPP and specifies the address on the local side. The first address on the define statement references the address of the host on the remote end of the interface; the address specified after this pointtopoint keyword defines the address on the local side of the interface.
An interface not defined as broadcast or pointtopoint is assumed to be nonbroadcast multi-access (NBMA), such as an X.25 network.
netmask mask: Specifies the subnetmask to be used on this interface. This is ignored on point-to-point interfaces.
multicast: Specifies that the interface is multicast capable.

An interface_list is a list of references to interfaces or groups of interfaces. There are four methods available for referring to interfaces. They are listed here from most general to most specific.

all: Specifies the word ``all'' to refer to all available interfaces.
Interface name wildcard: Specifies a wildcard name for all interfaces of the same type. For example, specify ``wdn'' to match all interfaces using Western Digital device drivers.
Interface name: Refers to a specific interface, usually one physical interface, which is specified as an alphabetic part followed by a numeric part. This will match one specific interface. For example, wdn0.
Interface address: Matches one specific interface. The reference can be by protocol address (for example, 10.0.0.51) or by symbolic hostname (for example, nic.ddn.mil). Note that a symbolic hostname reference is only valid when it resolves to only one address. Use of symbolic hostnames is not recommended.

If many interface lists are present in the configuration file with more than one parameter, these parameters are collected at runtime to create the specific parameter list for a given interface. If the same parameter is specified on more than one list, the parameter with the most specific interface is used.