Frame Relay Notes - LMI, Headers, and Encapsulation

Local Management Interface

• Manages link between the router and frame relay switch
• Routers send Status Enquiry to the switch
• The switch responds with a Status message informing the router of the DLCIs available
• Serves as a keepalive
• Default keepalive is 10 seconds, 3 misses is failed
• Three types
  • cisco <- default
  • ansi (Annex D)
  • q933a

R1(config)#interface s1/0
R1(config-if)#frame-relay lmi-type ansi

Headers and Encapsulation

• Link Access Procedure for Frame-mode Bearer Services (LAPF) is the first header
  • Includes DLCI, DE, FECN, BECN
  • To be read by the frame relay switch
• Frame relay encapsulation header is next
  • To be read by the router on the other end of the VC
• Two types
  • cisco : proprietary <- default
  • ietf : IETF RFC 2427

R1(config)#interface s1/0
R1(config-if)#frame-relay encapsulation ietf <- for all DLCIs
- or -
R1(config-if)#frame-relay interface-dlci 100 ietf <- for specific DLCIs
- or - 
R1(config-if)#frame-relay map ip 10.0.0.1 ietf <- for specific DLCis