Frame Relay Notes

Just some Frame Relay notes I’ve made in my studies.


PVC Status Messages-
Active - Working
Inactive - remote problem - problem on the other side 
Deleted - Local problem (problem on the immediate device)

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Three types of LMI: 
Cisco -default propreitary 
ANSI
Q933A
LMI Autosense used from the DTE side to determine the LMI type coming from the frame-relay provider. It sends out the three LMI messages and the LMI type based on what it recieves back.3 LMIs not recieved is the default for a time out and connection to be considered down.
router#show frame LMI - shows what type of LMI is being used, how many enq. has been sent and recieved.
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DLCI - Data Link Connection Identifier. Frame Relay's Layer 2 address. Locally Significant only. Not advertised to other routers.
Assigned by the frame relay provider.
iARP - Inverse ARP - Dynamic Mapping - Router's service to learn the discover the FRcircuit dynamically and create frame-map statements. 
Enabled by default.

Frame map statements: Always map the local DLCI to the remote IP address.
commands:
router(config-if)#encapsulation frame-relay - to turn frame relay on an interface. (Cisco or ietf are your encapsulation options.
router#show frame map - show frame relay map statements created statically or via iARP
router(config-if)#no frame-relay inverse-arp - turn off iARP (disable dynamic mapping)
router(config-if)#frame map ip x.x.x.x(remote router) xxx(local dlci) broadcast(to send out routing updates for routing protocols since FR is an NBMA network)

Split Horizon - Rule that routes learned on an interface are not to be sent out that same interface. Split Horizon is a routing loop prevention rule. Problem in frame-relay using point to point connections.
router(config-if)#no ip split horizon - turns off the split horizon rule.
Point to Multipoint is a way to prevent this. This is done by creating logical subinterfaces off a physical interface.
router(config)#interface serial 0/0.### specify point to point or multipoint.

Congestion notification values:
FECN - Forward Explicit Congestion Notification
BECN - Backward Explicit Congestion Notification
DE - Discard Eligible
router#show frame pvc - will show you pvc interfaces, will display in/out FECN and BECN values
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