Frame Relay is one of the most popular WAN protocols in the world. This technology
will become even more critical as corporations stretch their networks globally and the Internet
becomes more pervasive.
To become a successful CCNP, you need to understand the Frame Relay protocol. This technology
makes up the majority of the world’s non-dedicated circuits, and its importance cannot
be underestimated.
Frame Relay is the distant cousin to X.25, without some of X.25’s overhead. It does provide
congestion notification, which can be used with traffic shaping to help traffic response. Like
X.25, Frame Relay provides for permanent and switched virtual circuits.
LMI is an extension to the Frame Relay protocol developed by the Frame Relay Forum and
is used to provide management for virtual circuits. This makes the management of DLCI information
easier for the network administrator.
Cisco provides for a mechanism to enable a multipoint interface such as Frame Relay to look
like multiple virtual point-to-point or multipoint interfaces called subinterfaces. Point-to-point
subinterfaces can be used to solve problems caused by distance-vector routing protocols running
over multipoint interfaces.
Setting up a Cisco router as a Frame Relay switch is not something that you would do often,
but it is a useful feature when you are working in a lab environment. There are many troubleshooting
commands that can be used to verify the configuration of Frame Relay on a Cisco
router. They can be used to see the DLCI-to-Network-layer-address mapping and the current
state of LMI on the router. Frame Relay is a technology used in many networks, and mastering
its configuration and operation will take you far in your networking career.