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264 Chapter 9: Frame Relay Connection Controlling Traffic Flow
You must also determine the nature, or cast type, of the subinterface to be created. In other
words, you must decide if the subinterface acts as a point-to-point connection or a point-to-
multipoint connection. If not specified, the subinterface defaults to a multipoint connection.
To specify the cast type, simply add the keywords point-to-point or multipoint to the end of
the interface designation when it's created. For example, interface serial0.1 point-to-point
creates a point-to-point subinterface and interface serial0.1 multipoint creates a point-to-
multipoint subinterface.
Step 2: Configure Frame Relay Encapsulation
To enable Frame Relay on the interface, simply issue the command encapsulation frame relay.
The encapsulation of the interface determines the way it should act because each encapsulation
is technology-specific.
The encapsulation specified at this point dictates the Layer 2 framing characteristics of the
packet passed to this specific interface from Layer 3. Once the Layer 2 framing is established,
the resulting frame can be passed down to the physical layer for transmission.
Step 3: Configure Protocol-Specific Parameters
For each protocol to be passed across the Frame Relay connection, you must configure
appropriate addressing. This addressing must be planned in advance.
For point-to-point connections, each individual circuit should have its own subnetwork
addressing and two available host addresses. In the instance of IP, each subinterface is assigned
a separate (and of course, unique) IP subnet. For IPX, each subinterface must have a unique IPX
network number, and so on. As with any other addressing scheme, each side of the link must
have a unique host address.
For point-to-multipoint connections, each subinterface also must have unique addressing.
However, a point-to-multipoint connection can (by its very nature) connect to multiple remote
sites. Thus, all sites sharing the point-to-multipoint connection are members of the same
subnetwork, no matter the number of connections or the protocol.
The cast type of the interface also dictates the manner in which DLCIs are assigned to the Frame
Relay interface. The next section covers this topic in detail.
Step 4: Configure Frame Relay Characteristics
You must define specific parameters for Frame Relay operation. The parameters include LMI
and DLCI configuration.
If you're using a release of IOS Software earlier than 11.2, you must specify the LMI type that
is being implemented. The Frame Relay service provider, or telco, should provide the LMI