Data Link Connection Identifiers (DLCI)
- frame relay switches forward frame based on DLCI to a Virtual Circuit (VC)
- locally significant
- frame relay switches replace DLCI with the source DLCI before it forwards
Local Management Interface (LMI)
- between router and frame relay switch
- Status Inquiry from DTE to switch
- switch replies with Status Message that contains DLCIs and VCs
- every 6th carries Full Status Message which contains more complete information about VCs
Keepalives
- LMI Status Enquiry (router) and Status (switch) function as keepalives
- interface fails after (default 3) keepalive intervals (default 10 seconds)
- config-if# [no] keepalive
Types
- Cisco - DLCI 16-1007 (992); LMI DCLI is 1023
- ANSI - DLCI 16-991 (976)
- ITU (q933a) - DLCI 16-991 (976)
- config-if# frame-relay lmi-type [cisco | ansi | q933a]
Headers & Encapsulation
- uses different consecutive headers
First Header
- ITU Link Access Procedure for Frame-Mode Bearer Services (LAPF)
- includes
- DLCI
- DE
- BECN
- FECN
- fields used by FR to deliver frames across cloud
Second Header
- important only to DTEs on end of VC
- two options
- Cisco proprietary header (default)
- IETF defined RFC 2427 header
- Network Layer Protocol ID (NLPID)
- config-if# encapsulation frame-relay ieft
- config-if# frame-relay interface-dlci <#> ieft
- config-if# frame-relay map dlci ... ieft
Congestion
- caused by speed mismatches
Adaptive Shaping
- uses FECN & BECN to inform router that VC is experiencing congestion
- when a switch notices congestion cause by VC, sets FECN
- when a switch sets a FECN, it tracks congested VC, next frame in opposite direction marked with BECN
- FECN can be set by frame relay switches, but not routers
- BECN can be set by routers and switches
- routers can watch for FECN
- config-pmap-c# shape fecn-adapt (CB)
- config-if# traffic-shape fecn-adapt (FRTS)
Discard Eligibility Bit
- when queues fill and frames must be dropped, switches can examine DE to decide
Configuration
Basics
- any DLCI learned with LMI that isn't associated with a subinterface will be used by physical interface
- Payload Compression
- three options
- packet-by-packet
- data stream
- Frame Relay Forum Implementation Agreement 9 (FRF.9; standardized)
- data stream compression (non proprietary)
- uses LZS compression
- dictionary - table of short codes and longer associated strings
- packet-by-packet clears the dictionary after each packet
- configured per VC
- config-if# frame-relay payload-compress [frf9 | data-stream | ???] stac
- config-if# frame-relay map ip ... 101 broadcast payload-compress [frf9 | data-stream | ???] stac
- three options
Fragmentation
- LFI over PVC defined in FRF.12
- dual FIFO queues
- high queue - FRTS LLQ packets
- normal queue - from other queuing
- recommended choosing fragment size so packets in LLQ PQ will not be fragmented
- config-if# frame-relay fragment <int> [end-to-end] (interface)
- config-if-dlci-c# frame-relay fragment <int> [end-to-end] (legacy; FRTS class)
LFI Using Multilink PPP (MLP)
- only option for Frame Relay-to-ATM Service Internetworking
- LMP over frame relay uses PPP headers
Requires
- QoS map policy that uses PQ with interleaving packets from this special queue
- requires multilink interface
- ip address
- service-policy command
Configure
- config-cmap# match dscp ef
- config-pmap-c# priority percent 10
- config# interface multilink1
- config-if# bandwidth 256
- config-if# ip address ...
- config-if# ppp multilink
- config-if# ppp multilink interleave
- config-if# ppp multilink group 1
- config-if# ppp multilink fragment delay 10
- config-if# service-policy output WORD
- config# interface virtual-template1
- config-if# no ip address
- config-if# ppp multilink
- config-if# ppp multilink group 1
- config# interface serial0/2
- config-if# no ip address
- config-if# encapsulation frame-relay
- config-if# no fair-queue
- config-if# frame-relay traffic-shaping
- config-if# frame-relay interface-dlci 111 ppp virtual-template1
Terms
Permanent Virtual Circuit (PVC)
Data Link Connection Identifier (DLCI)
Local Management Interface (LMI)
Network-to-Network Interface (NNI)
Local Access Route/Committed Information Rate (CIR)
Base Configuration
config# interface s0/0
config-if# encapsulation frame-relay
Sub-Interface Configuration
config# no frame-relay inverse-arp (don't ask)
config# no arp frame-relay (don't tell)
config# interface s0/0.1 point-to-point (configure sub interface)
config-subif# frame-relay interface-dlci 201 (point to point dlci mapping)
conf-fr-dlci#
config# interface s0/1.1 multipoint (configure sub interface)
config-subif# frame-relay map ip 192.168.1.1 102 broadcast (multipoint dlci mapping)
config-subif# no ip split-horizon eigrp 1(disable split horizon for eigrp)
View/Debug Commands
show frame-relay lmi
show frame-relay map
show frame-relay pvc
Traffic Shaping
Terms
Tc - Timing Interval (1/8 Sec)
Bc - Committed Burst
Be - Excess Burst
DE - Discard Eligible
BECN - Backwards Explicit Congestion Notification
FECN - Forwards Explicit Congestion notification
Basic Configuration
config# map-class frame-relay SLOW
config-map-class# frame-relay adaptive-shaping becn (listen tot he BECNs)
config-map-class# frame-relay mincir 24400 (BECN wont make it go any slower then this)
config-map-class# frame-relay bc 3600 (288000/8)
config-map-class# frame-relay be 200 (burst)
config-map-class# frame-relay cir 28800
config-map-class# frame-relay tc 125 (1/8 sec in milli)
config-map-class# traffic-rate 28800 30000 (sets cir and be)
config# interface s0/0.1
config-subif# frame-relay class SLOW (applies to all DLCIs)
config# interface s0/1.1
config-subif# frame-relay interface-dlci 102
config-fr-dlci# class slow (applies to specific DLCI)
View/Debug Commands
show traffic-shape
show compress
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