An interface statement defines configuration options for the network
interfaces. The interface_list identifies the
interfaces affected by the configuration options. The interfaces in the
list are identified by interface name (e.g., le0), by hostname, by IP
address, or by the keyword all. The
keyword all refers to every interface
on the system. The interface name can refer to a single interface or a
group of interfaces. For example, an interface name of eth0 refers to
the interface eth0, whereas the name le refers to all installed
interfaces that start with the letters le (which might include le0, le1,
and le2). A hostname can be used if it resolves to only one
address.
Most system administrators prefer to use the IP address to identify an interface. After all, IP addresses are inherently a part of TCP/IP, and it’s TCP/IP routing that this file configures.
Additionally, remote systems know this interface by its IP address, not its interface name. Finally, DNS may provide more than one address for a hostname, and future Unix operating systems may allow more than one address per interface. IP addresses are safest.
gated supports four types of
interfaces: loopback, broadcast, point-to-point, and
nonbroadcast multiple access (NBMA). All of these are discussed in the
text of this book except for NBMA. It is a multiple access interface,
but the underlying network is not capable of broadcast. Examples are
Frame Relay and X.25.
gated ignores any interface in
the list that has an invalid local, remote, or broadcast address, or an
invalid subnet mask. gated also
ignores a point-to-point interface that has the same local and remote
addresses. gated assumes that
interfaces that are not marked UP by the kernel do not exist.
The syntax of the interfaces statement is:
interfaces {
options
[strictinterfaces]
[scaninterval time]
[ aliases-nexthop ( primary | lowestip | keepall ) ];
interface interface_list
[preference preference]
[down preference preference]
[passive]
[simplex]
[reject]
[blackhole]
[ AS autonomoussystem ];
define address
[broadcast address] | [pointopoint address]
[netmask mask]
[multicast] ;
} ;The configuration options defined before the interface list are global options. The global options are:
strictinterfacesGenerates a fatal error if an interface referenced in the
configuration file is not found when gated scans the kernel at startup and is
not listed in a define
statement. (See the define
option later in this section.) Normally a warning message is
issued and gated continues
running.
scaninterval
timeSpecifies 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 also scans
the interface list on receipt of a SIGUSR2.
aliases-nexthop ( primary | lowestip | keepall )Defines the next-hop address that gated installs for interface routes.
primary, which is the default,
uses the primary interface address as the gateway for an interface
route. lowestip uses the lowest
IP address as the next-hop address. keepall retains all interface routes in
the kernel.
The interface command defines
the interface_list and all of the options
that affect the specified interfaces. Options available on this
statement are:
preference
preferenceSets the preference for this interface. The value
preference is a number between 0 and
255. gated prefers routes
through interfaces with low preference numbers. The default
preference for all directly attached network interfaces is
0.
down preference
preferenceSets the preference used when gated believes an interface is not
functioning properly. The default is 120.
passivePrevents gated from
downgrading the preference of the interface when it is not
functioning properly. gated
assumes that an interface is down when it stops receiving routing
information through that interface. gated performs this check only if the
interface is actively participating in a routing protocol.
simplexSpecifies that gated
should not use packets generated by this system as an indication
that the interface is functioning properly. Only packets from
remote systems are used to indicate that the interface is
operating.
reject | blackholeEither of these keywords identifies the interface as the “blackhole interface” used to install rejected routes in the kernel. (See the control statements for more about rejected routes.) This is available only on BSD systems that have installed a reject/blackhole pseudo-interface.
AS
autonomoussystemIdentifies the autonomous system number that gated should use when creating an AS
path vector for this route. You should recall that some routing
protocols, such as BGP, associate an AS path with a route.
The define
address command lists interfaces that might
not be present when gated scans the
kernel interface list at startup. It overrides the strictinterfaces option for the interface
defined by address. Possible options for the
define command are:
broadcast
addressDefines the broadcast address.
pointopoint
addressDefines the local address for a point-to-point interface.
(See Chapter 6 for a discussion
of point-to-point interfaces.) When this option is used, the
address on the define statement
specifies the address of the remote host, and the address
specified after the pointopoint
keyword defines the local address. Don’t use both broadcast and pointopoint in the same define.
netmask
maskDefines the subnet mask.
multicast