Cisco CCNA 640-802 - CCENT Certification Exam Training: Frame Relay LMI And LMI Autosense

For success on your CCNA 640-802 and CCENT exams, you absence to understand how and why Frame Relay LMI messages operate. You need to understand this for real-world networking as well, since Frame Relay is frequent in today's networks - and without LMI, you have no Frame Relay!

The Local Management Interface (LMI) messages are sent among the DCE, typically the service provider, and the DTE, the Cisco router. LMI Status messages serve as keepalives for the border connection. If keepalives are not continually received at either the DCE and DTE, the frame connection will drop. The LMI likewise indicates the PVC status to the router, reflected as either athletic or lazy.

The LMI types must mate on the DTE and DCE for the PVC apt be created. There are 3 types of LMI:

Cisco (the default)

ansi

q933a

The LMI type can be changed with the frame lmi-type command. Before act everything with the frame relay commands, although, we have to empower frame relay on the interface with the encapsulation frame-relay command. Remember, the default encapsulation type on a Cisco Serial interface namely HDLC.

R1(config)#interface serial0

R1(config-if)#encapsulation ?

atm-dxi ATM-DXI encapsulation

frame-relay Frame Relay networks

hdlc Serial HDLC synchronous

lapb LAPB (X.25 Level 2)

ppp Point-to-Point protocol

smds Switched Megabit Data Service (SMDS)

x25 X.25

R1(config-if)#encapsulation frame-relay

R1(config-if)#frame-relay lmi-type ?

cisco

ansi

q933a

We tin hardcode the LMI type as shown in namely example, and there's variant access to obtain the LMI to match with the remote DCE. LMI Autosense has the router send out one LMI Status information for entire three LMI types.

The router then waits for a reaction for one of those LMI types from the DCE. When the router sees the reaction to its LMI Autosense messages, the router will then send merely the same LMI type it received from the DCE.

On rare causes - such as your CCNA exam, perhaps :) - the Frame LMI may no match. We'll take a look by such a scenario in the next installment of my exclusive Cisco CCENT / CCNA 640-802 appraisal exam tutorial array!