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 ietf <- for specific DLCis