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FRAME-RELAY

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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 SwitchConfigure terminalframe-relay switchinginterface 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 701frame-relay route 108 interface Serial8 801frame-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