Transcript Slide 1
FRAME-RELAY Kevin Large 1 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. Kevin Large 2 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. Kevin Large 3 What is Frame-relay Kevin Large 4 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. Kevin Large 5 Frame-relay LMI debug Kevin Large 6 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. Kevin Large 7 FRAME-SWITCH FULL MESH Kevin Large 8 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 Kevin Large 9 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. Kevin Large 10 FRAME-RELAY CONFIGURATION Kevin Large 11 LAB CONFIGURATION Kevin Large 12