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FRAME-RELAY
Kevin Large
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What is Frame-relay
• Frame-relay is a packet switching technology that offers fast flexible
networking.
• Typical Frame-relay interfaces can operate at transmission rates
ranging from 56 Kbps to 45 Mbps.
• Frame-relay provide high speed connections between widely
dispersed Local Area Networks (LAN’s).
• Frame-relay is a connection oriented service, it creates logical
connections called Permanent Virtual Circuits (PVC’s) between the
sending and receiving router interfaces.
• A PVC defines the route that the frame will take when travelling
between stations on a frame-relay network.
• The PVC between any two stations on a frame-relay network is
identified by a number known as a Data Link Connection Identifier
(DLCI) on each end of the PVC.
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What is Frame-relay
• A single physical interface on a router can have many PVC’s with
each PVC going to a different destination, but each of these PVC’s
must have a unique DLCI associated with it.
• The DLCI is locally significant on the router and can be any number
between 16 – 1007.
• The DLCI can be assigned manually, it is then known as a static
DLCI.
• Or the DCLI can be obtained from the frame switch automatically
using inverse-arp, then its known as a dynamic DLCI.
• A frame-relay pvc can have three possible values, active, inactive or
deleted.
• You can use the show frame-relay pvc command from privileged
mode to view information regarding the PVC’s and DLCI’s.
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What is Frame-relay
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Frame-relay LMI
• The frame-relay LMI (local management interface) is used by the
customer to monitor the link between their router (DTE) and the
service providers frame switch (DCE)
• There are three types of frame-relay LMI, they are Cisco, ANSI and
q933a
• The local management interface communicates over specific DLCI’s
Cisco uses DLCI 1023 whilst both ANSI and q933a use DLCI 0
• LMI status messages combined with Inverse ARP messages allow a
router to associate network layer ip addresses and data link layer
DLCI addresses.
• When a router that is connected to a frame-relay network is started,
it sends an LMI status inquiry message to the frame switch
• The frame switch replies with an LMI status message containing
details of every virtual circuit configured on the access link.
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Frame-relay LMI debug
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The Frame Switch
• The frame switch is nearly always the property of the service
provider, and as such is there responsibility to configure.
• Its job is simply to switch frame-relay encapsulated frames entering
one port (the ingress port) to the correct exiting port (egress port).
• It does this by having a pre-defined set of routes configured that
map an incoming frames DLCI to an outgoing switch port, these
frame-relay routes can become quite extensive.
• It is possible to make a Cisco router operate as a frame switch, by
entering the command frame-relay switching, which will cause it to
switch frames at Layer 2 instead of switching IP packets at Layer 3.
• This is very useful for lab configurations as it allows you to
experience the full range of frame-relay configuration examples.
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FRAME-SWITCH FULL MESH
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The Frame Switch
Configure terminal
frame-relay switching
interface Serial1
no ip address
encapsulation frame-relay
clock rate 64000
frame-relay intf-type dce
frame-relay route 102 interface Serial2 201
frame-relay route 103 interface Serial3 301
frame-relay route 104 interface Serial4 401
frame-relay route 105 interface Serial5 501
frame-relay route 106 interface Serial6 601
frame-relay route 107 interface Serial7 701
frame-relay route 108 interface Serial8 801
frame-relay route 109 interface Serial9 901
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Frame-relay step by step
• Set the layer 2 (data-link layer) encapsulation to frame-relay on the
physical interface, using the interface configuration mode command
encapsulation frame-relay [ cisco | ietf ]
• Enter the command no frame-relay inverse-arp to stop the router
automatically mapping all the DLCI’s that exist on the frame switch.
• Allow the interface to send and receive frame-relay frames by
entering no shutdown.
• In the real world it is best to create sub-interfaces, then apply the
layer 3 configuration (IP addresses) to these sub-interfaces.
• Using point-to-point sub-interfaces stops the problem known as
split-horizon which can destroy the routing process in your network.
• Finally on the point-to-point sub-interface you define the out-going
DLCI using the frame-relay interface-dlci command.
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FRAME-RELAY CONFIGURATION
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LAB CONFIGURATION
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