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Chapter 10
Wide Area Networking Protocols
Beginning with IOS version 11.2, the LMI type is auto-sensed. This enables the
interface to determine the LMI type supported by the switch.
If you're not going to use the auto-sense feature, you'll need to check with
your Frame Relay provider to find out which type to use instead. The default
type is Cisco, but you may need to change to ANSI or Q.933A. The three
different LMI types are depicted in the following router output:
RouterA(config-if)#frame-relay lmi-type ?
cisco
ansi
q933a
As seen in the output, all three standard LMI signaling formats are
supported:
Cisco LMI defined by the Gang of Four (default).
ANSI Annex D defined by ANSI standard T1.617.
ITU-T (q933a) Annex A defined by Q.933.
Routers receive LMI information on a frame-encapsulated interface and
update the virtual circuit status to one of three different states:
Active state Everything is up, and routers can exchange information.
Inactive state The router's interface is up and working with a connec-
tion to the switching office, but the remote router is not working.
Deleted state No LMI information is being received on the interface
from the switch. It could be a mapping problem or a line failure.
Subinterfaces
You can have multiple virtual circuits on a single serial interface and yet treat
each as a separate interface. These are known as subinterfaces. Think of
a subinterface as a hardware interface defined by the IOS software. An
advantage gained through using subinterfaces is the ability to assign different
Network layer characteristics to each subinterface and virtual circuit, such as
IP routing on one virtual circuit and IPX on another.
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