B.6. Interface Statements
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
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:
[ aliases-nexthop ( primary | lowestip | keepall ) ];
[down preference preference]
[ AS autonomoussystem ];
[broadcast address] | [pointopoint address]
The configuration options defined before the interface list are
global options. The global options are:
Generates 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
- 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 also scans the interface list on receipt of
- 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
- preference preference
Sets 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 preference
Sets the preference used when gated believes an
interface is not functioning properly. The default is 120.
Prevents 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.
Specifies 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 | blackhole
Either 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
- AS autonomoussystem
Identifies 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 address
Defines the broadcast address.
- pointopoint address
Defines the local address for a point-to-point interface. (See Chapter 6, "Configuring the Interface " 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 mask
Defines the subnet mask.
Specifies that the interface supports multicasting.
Copyright © 2002 O'Reilly & Associates. All rights reserved.