Information Technology Reference
In-Depth Information
Montecito#
show interfaces ethernet 0
Ethernet0 is
up
, line protocol is
up
Hardware is Lance, address is . . .
What about a dialer interface that is not connected? If the protocol is not up and running on the interface,
the implication is that the interface itself will not be up; routes that rely on that interface will be flushed
from the routing table, and traffic will not be routed to that interface. The result would be that no calls
would be initiated by the interface.
To counter this possibility, any interface that is configured as a dialer interface (for example, a Serial or
Async interface with the command
dialer in-band
or
dialer dtr
) or that, by its nature, is a dialer
interface (BRIs and PRIs), will be in a state of up/up (spoofing):
Montecito#
show interfaces bri 0
BRI0 is
up
, line protocol is
up (spoofing)
Hardware is BRI
Internet address is . . .
In other words, the interface pretends to be up/up so that associated routes will remain in force and so
that packets can be routed to the interface.
In some circumstances, a dialer interface will not be up/up (spoofing). The
show interface
output may
show it as being administratively down:
Montecito#
show interfaces bri 0
BRI0 is
administratively down
, line protocol is down
Hardware is BRI
Internet address is . . .
Administratively down
merely means that the interface has been configured with the command
shutdown
. This is the default state of any router interface when the router is booted for the very first
time. To remedy this, use the interface configuration command
no shutdown
.
The interface may also be seen to be in standby mode:
Montecito#
show interfaces bri 0
BRI0 is standby mode, line protocol is down
Hardware is BRI
Internet address is . . .
This state indicates that the interface has been configured as the backup for another interface. When a
connection requires redundancy in case of failure, a dialer interface can be set up as the backup. This is
accomplished by adding the following commands to the primary connection's interface:
backup interface [interface]
backup delay [enable-delay] [disable-delay]
After the
backup interface
command has been configured, the interface used as the backup will be put
into standby mode until the primary interface goes to a state of
down/down.
At that time, the dialer
interface configured as a backup will go to a state of up/up (spoofing) pending a dial event.
