Mạng máy tính cơ bản - Chapter 3: Frame - Relay

1Chapter 3 – Frame-Relay CCNA Exploration 4.0 Học viện mạng Bach Khoa - Website: www.bkacad.com 2 Introduction Học viện mạng Bach Khoa - Website: www.bkacad.com 3 Basic Frame Relay Concepts Học viện mạng Bach Khoa - Website: www.bkacad.com 4 Introducing Frame Relay Frame Relay: An Efficient and Flexible WAN Technology • Frame Relay has become the most widely used WAN technology in the world. Large enterprises, governments, ISPs, and small businesses use Frame Relay, primarily because of its price and flexibility. • Moreover, Frame Relay provides greater bandwidth, reliability, and resiliency than private or leased lines • Frame Relay reduces network costs by using less equipment, less complexity, and an easier implementation. Học viện mạng Bach Khoa - Website: www.bkacad.com 5 Introducing Frame Relay • In the example shown in the figure, Span Engineering has five campuses across North America. • The bandwidth requirement of each site: Học viện mạng Bach Khoa - Website: www.bkacad.com 6 Introducing Frame Relay The first Solution – Leased line • Using leased lines, each Span site is connected through a switch at the local telephone company's central office (CO) through the local loop, and then across the entire network. • These lines are truly dedicated in that the network provider reserves that line for Span's own use. There is no sharing, and Span is paying for the end-to-end circuit regardless of how much bandwidth it uses. Học viện mạng Bach Khoa - Website: www.bkacad.com 7 Introducing Frame Relay The second Solution – Frame Relay • Frame Relay is a more cost-effective option for two reasons. – First, with dedicated lines, customers pay for an end-to-end connection. That includes the local loop and the network link. • With Frame Relay, customers only pay for the local loop, and for the bandwidth they purchase from the network provider. – The second reason for Frame Relay's cost effectiveness is that it shares bandwidth across a larger base of customers. Học viện mạng Bach Khoa - Website: www.bkacad.com 8 Introducing Frame Relay • The table shows a representative cost comparison for comparable ISDN and Frame Relay connections. Học viện mạng Bach Khoa - Website: www.bkacad.com 9 Introducing Frame Relay • The Flexibility of Frame Relay – A virtual circuit provides considerable flexibility in network design. – In Frame Relay, the end of each connection has a number to identify it called a Data Link Connection Identifier (DLCI). – Any station can connect with any other simply by stating the address of that station and DLCI number of the line it needs to use. Học viện mạng Bach Khoa - Website: www.bkacad.com 10 Introducing Frame Relay The Frame Relay WAN • In the late 1970s and into the early 1990s, the WAN technology joining the end sites was typically using the X.25 protocol. However, X.25 have much overhead to the protocol. • Frame Relay has lower overhead than X.25 because it has fewer capabilities. For example, Frame Relay does not provide error correction, modern WAN facilities offer more reliable connection services and a higher degree of reliability than older facilities. Học viện mạng Bach Khoa - Website: www.bkacad.com 11 Introducing Frame Relay Frame Relay Operation • The connection between a DTE device and a DCE device consists of both a physical layer component and a link layer component: – The physical component defines the mechanical, electrical, functional, and procedural specifications for the connection between the devices. – The link layer component defines the protocol that establishes the connection between the DTE device, such as a router, and the DCE device, such as a switch. Học viện mạng Bach Khoa - Website: www.bkacad.com 12 Virtual Circuits • The connection through a Frame Relay network between two DTEs is called a virtual circuit (VC). The circuits are virtual because there is no direct electrical connection from end to end. • There are 2 ways to establish VCs: – SVCs, switched virtual circuits, are established dynamically by sending signaling messages to the network (CALL SETUP, DATA TRANSFER, IDLE, CALL TERMINATION). – PVCs, permanent virtual circuits, are preconfigured by the carrier, and after they are set up, only operate in DATA TRANSFER and IDLE modes. Học viện mạng Bach Khoa - Website: www.bkacad.com 13 Virtual Circuits Local Significance • VCs provide a bidirectional communication path from one device to another. VCs are identified by DLCIs. DLCI values typically are assigned by the Frame Relay service provider (for example, the telephone company). • Frame Relay DLCIs have local significance, which means that the values themselves are not unique in the Frame Relay WAN. Học viện mạng Bach Khoa - Website: www.bkacad.com 14 Virtual Circuits Idenfiying VCs • Frame Relay labels each VC with a DLCI. • The DLCI is stored in the address field of every frame transmitted to tell the network how the frame should be routed. • The Frame Relay service provider assigns DLCI numbers. Usually, DLCIs 0 to 15 and 1008 to 1023 are reserved for special purposes. Therefore, service providers typically assign DLCIs in the range of 16 to 1007. Học viện mạng Bach Khoa - Website: www.bkacad.com 15 Virtual Circuits Multiple VCs • Frame Relay is statistically multiplexed, meaning that it transmits only one frame at a time, but that many logical connections can co-exist on a single physical line. • The Frame Relay Access Device (FRAD) or router connected to the Frame Relay network may have multiple VCs connecting it to various endpoints. • Multiple VCs on a single physical line are distinguished because each VC has its own DLCI. Học viện mạng Bach Khoa - Website: www.bkacad.com 16 Virtual Circuits • For example, Span Engineering has five locations, with its headquarters in Chicago. Chicago is connected to the network using five VCs and each VC is given a DLCI. Học viện mạng Bach Khoa - Website: www.bkacad.com 17 Frame Relay Encapsulation • Frame Relay takes data packets from a network layer protocol, such as IP or IPX, encapsulates them as the data portion of a Frame Relay frame, and then passes the frame to the physical layer for delivery on the wire. Học viện mạng Bach Khoa - Website: www.bkacad.com 18 Frame Relay Topologies • There are three topology types: star, full mesh, or partial mesh. Học viện mạng Bach Khoa - Website: www.bkacad.com 19 Frame Relay Topologies • A fully meshed topology means that each node on the periphery of a given packet-switching network has a direct path to every other node on the cloud. Học viện mạng Bach Khoa - Website: www.bkacad.com 20 Frame Relay Topologies • A partially meshed topology reduces the number of routers within a region that have direct connections to all other nodes in the region. Học viện mạng Bach Khoa - Website: www.bkacad.com 21 DLCI • A data-link connection identifier (DLCI) identifies the logical VC between the CPE and the Frame Relay switch. • The Frame Relay switch maps the DLCIs between each pair of routers to create a PVC. • DLCIs have local significance, although there some implementations that use global DLCIs. • DLCIs 0 to 15 and 1008 to 1023 are reserved for special purposes. • Service providers assign DLCIs in the range of 16 to 1007. – DLCI 1019 - 1022: Multicasts – DLCI 1023: Cisco LMI – DLCI 0: ANSI LMI Học viện mạng Bach Khoa - Website: www.bkacad.com 22 Frame Relay Address Mapping • Cisco routers support all network layer protocols over Frame Relay, such as IP, IPX, and AppleTalk. This address-to-DLCI mapping can be accomplished either by static or dynamic mapping: – Manual • Manual: Administrators use a frame relay map statement. – Dynamic • Inverse Address Resolution Protocol (I-ARP) provides a given DLCI and requests next-hop protocol addresses for a specific connection. • The router then updates its mapping table and uses the information in the table to forward packets on the correct route. Học viện mạng Bach Khoa - Website: www.bkacad.com 23 Frame Relay Address Mapping Học viện mạng Bach Khoa - Website: www.bkacad.com 24 Inverse ARP • Once the router learns from the switch about available PVCs and their corresponding DLCIs, the router can send an Inverse ARP request to the other end of the PVC. (unless statically mapped) • For each supported and configured protocol on the interface, the router sends an Inverse ARP request for each DLCI. (unless statically mapped) • In effect, the Inverse ARP request asks the remote station for its Layer 3 address. • At the same time, it provides the remote system with the Layer 3 address of the local system. • The return information from the Inverse ARP is then used to build the Frame Relay map. 12 Học viện mạng Bach Khoa - Website: www.bkacad.com 25 Inverse ARP • Inverse Address Resolution Protocol (Inverse ARP) was developed to provide a mechanism for dynamic DLCI to Layer 3 address maps. • Inverse ARP works much the same way Address Resolution Protocol (ARP) works on a LAN. • However, with ARP, the device knows the Layer 3 IP address and needs to know the remote data link MAC address. • With Inverse ARP, the router knows the Layer 2 address which is the DLCI, but needs to know the remote Layer 3 IP address. Học viện mạng Bach Khoa - Website: www.bkacad.com 26 Inverse ARP • On a Cisco router, Inverse ARP is on by default when an interface is configured to use Frame Relay encapsulation. • If static mapping for a specific DLCI is configured, Inverse ARP is automatically disabled for the specified protocol on the specified DLCI. • Use static mapping if the router at the other end either does not support Inverse ARP or does not support Inverse ARP for a specific protocol being used over Frame Relay. Học viện mạng Bach Khoa - Website: www.bkacad.com 27 Inverse ARP Limitations • Inverse ARP only resolves network addresses of remote Frame-Relay connections that are directly connected. • Inverse ARP does not work with Hub-and-Spoke connections. • When using dynamic address mapping, Inverse ARP requests a next-hop protocol address for each active PVC. • Once the requesting router receives an Inverse ARP response, it updates its DLCI-to-Layer 3 address mapping table. • Dynamic address mapping is enabled by default for all protocols enabled on a physical interface. • If the Frame Relay environment supports LMI autosensing and Inverse ARP, dynamic address mapping takes place automatically. • Therefore, no static address mapping is required. Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane 172.16.1.1172.16.1.2 DLCI 101 DLCI 102 Học viện mạng Bach Khoa - Website: www.bkacad.com 28 Local Management Interface (LMI) • LMI is a signaling standard between the DTE and the Frame Relay switch. • LMI is responsible for managing the connection and maintaining the status between devices. • LMI Extensions: – VC status messages – Multicasting – Global addressing – Simple flow control Học viện mạng Bach Khoa - Website: www.bkacad.com 29 Local Management Interface (LMI) • Starting with Cisco IOS software release 11.2, the default LMI autosense feature detects the LMI type supported by the directly connected Frame Relay switch. Based on the LMI status messages it receives from the Frame Relay switch, the router automatically configures its interface with the supported LMI type acknowledged by the Frame Relay switch. Học viện mạng Bach Khoa - Website: www.bkacad.com 30 Local Management Interface (LMI) Học viện mạng Bach Khoa - Website: www.bkacad.com 31 Using LMI and Inverse ARP to Map Addresses Học viện mạng Bach Khoa - Website: www.bkacad.com 32 Frame Relay Address Mapping • Activity 3.1.5.5 Học viện mạng Bach Khoa - Website: www.bkacad.com 33 Configuring Frame Relay Học viện mạng Bach Khoa - Website: www.bkacad.com 34 Frame Relay Configuration Tasks Học viện mạng Bach Khoa - Website: www.bkacad.com 35 Enable Frame Relay Encapsulation • Step 1. Setting the IP Address on the Interface • Step 2. Configuring Encapsulation R(config-if)# encapsulation frame-relay [cisco | ietf] • Step 3. Setting the Bandwidth • Step 4. Setting the LMI Type (optional) Học viện mạng Bach Khoa - Website: www.bkacad.com 36 Enable Frame Relay Encapsulation Học viện mạng Bach Khoa - Website: www.bkacad.com 37 Configuring a Static Frame Relay Map • Static mapping is manually configured on a router. Establishing static mapping depends on your network needs. Router(config-if)# frame-relay map protocol protocol-address dlci [broadcast] [ietf | cisco] • Enable/Disables FR Inverse ARP (config-if)# no frame-relay inverse-arp – • Note: – (config-if)# no frame-relay inverse-arp Disables the sending of Inverse ARP requests. Học viện mạng Bach Khoa - Website: www.bkacad.com 38 Học viện mạng Bach Khoa - Website: www.bkacad.com 39 Configuring a Static Frame Relay Map Học viện mạng Bach Khoa - Website: www.bkacad.com 40 Remote IP Address Local DLCIUses cisco encapsulation for this DLCI (not needed, default) By default, cisco is the default encapsulation Example Học viện mạng Bach Khoa - Website: www.bkacad.com 41 Configuring a Static Frame Relay Map • If the Cisco encapsulation is configured on a serial interface, then by default, that encapsulation applies to all VCs on that serial interface. • If the equipment at the destination is Cisco and non-Cisco, configure the Cisco encapsulation on the interface and selectively configure IETF encapsulation per DLCI, or vice versa. Applies to all DLCIs unless configured otherwise Học viện mạng Bach Khoa - Website: www.bkacad.com 42 Case study: Hub and Spoke Topology Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 Hub Router Spoke Routers Học viện mạng Bach Khoa - Website: www.bkacad.com 43 HubCity interface Serial0 ip address 172.16.1.2 255.255.255.0 encapsulation frame-relay Spokane interface Serial0 ip address 172.16.1.1 255.255.255.0 encapsulation frame-relay Spokomo interface Serial0 ip address 172.16.1.3 255.255.255.0 encapsulation frame-relay Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 Configuration using Inverse ARP • Router-DTE(config)# interface s0/0/0 • encapsulation frame-relay • frame-relay lmi-type {cisco|ansi|q933} • bandwidth {64| } • Router-DTE# show frame-relay pvc • Router-DTE# show frame-relay lmi • Router-DTE# show frame-relay map • Router-DTE# show ip interface brief • Router-DTE# show running-config Học viện mạng Bach Khoa - Website: www.bkacad.com 44 • R-DTE# clear frame-relay inarp • Clear ip route * Học viện mạng Bach Khoa - Website: www.bkacad.com 45 Học viện mạng Bach Khoa - Website: www.bkacad.com 46 HubCity# show frame-relay map Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 102, dynamic, broadcast, status defined, active Spokomo# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 211, dynamic, broadcast, status defined, active Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 Configuration using Inverse ARP Học viện mạng Bach Khoa - Website: www.bkacad.com 47 • Inverse ARP resolved the ip addresses for HubCity for both Spokane and Spokomo • Inverse ARP resolved the ip addresses for Spokane for HubCity • Inverse ARP resolved the ip addresses for Spokomo for HubCity • What about between Spokane and Spokomo? HubCity# show frame-relay map Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 102, dynamic, broadcast, status defined, active Spokomo# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 211, dynamic, broadcast, status defined, active Configuration using Inverse ARP Học viện mạng Bach Khoa - Website: www.bkacad.com 48 Inverse ARP Limitations • Can HubCity ping both Spokane and Spokomo? Yes! • Can Spokane and Spokomo ping HubCity? Yes! • Can Spokane and Spokomo ping each other? No! The Spoke routers’ serial interfaces (Spokane and Spokomo) drop the ICMP packets because there is no DLCI-to-IP address mapping for the destination address. • Solutions to the limitations of Inverse ARP 1. Add an additional PVC between Spokane and Spokomo (Full Mesh) 2. Configure Frame-Relay Map Statements 3. Configure Point-to-Point Subinterfaces. Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 Học viện mạng Bach Khoa - Website: www.bkacad.com 49 Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 HubCity interface Serial0 ip address 172.16.1.2 255.255.255.0 encapsulation frame-relay (Inverse-ARP still works here) Spokane interface Serial0 ip address 172.16.1.1 255.255.255.0 encapsulation frame-relay frame-relay map ip 172.16.1.3 102 frame-relay map ip 172.16.1.2 102 Spokomo interface Serial0 ip address 172.16.1.3 255.255.255.0 encapsulation frame-relay frame-relay map ip 172.16.1.1 211 frame-relay map ip 172.16.1.2 211 Frame-Relay Map Statements Notice that the routers are configured to use either IARP or Frame Relay maps. Using both on the same interface will cause problems. Học viện mạng Bach Khoa - Website: www.bkacad.com 50 Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 • The previous configuration works fine and all routers can ping each other. • What if we were to use I-ARP between the spoke routers and the hub, and frame relay map statements between the two spokes? • There would be a problem! Inverse ARP Mixing Inverse ARP and Frame Relay Map Statements Frame Relay maps Học viện mạng Bach Khoa - Website: www.bkacad.com 51 HubCity interface Serial0 ip address 172.16.1.2 255.255.255.0 encapsulation frame-relay Spokane interface Serial0 ip address 172.16.1.1 255.255.255.0 encapsulation frame-relay frame-relay map ip 172.16.1.3 102 Spokomo interface Serial0 ip address 172.16.1.3 255.255.255.0 encapsulation frame-relay frame-relay map ip 172.16.1.1 211 Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 Mixing Inverse ARP and Frame Relay Map Statements Học viện mạng Bach Khoa - Website: www.bkacad.com 52 HubCity# show frame-relay map Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 102, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, status defined, active Spokomo# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 211, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO, status defined, active Mixing Inverse ARP and Frame Relay Map Statements Học viện mạng Bach Khoa - Website: www.bkacad.com 53 Good News: • Everything looks fine! • Now all routers can ping each other! Bad News: • Problem when using Frame-Relay map statements AND Inverse ARP. • This will only work until the router is reloaded, here is why... Mixing Inverse ARP and Frame Relay Map Statements HubCity# show frame-relay map Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 102, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, status defined, active Spokomo# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 211, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO, status defined, active Học viện mạng Bach Khoa - Website: www.bkacad.com 54 Frame-Relay Map Statement Rule: • When a Frame-Relay map statement is configured for a particular protocol (IP, IPX, ) Inverse-ARP will be disabled for that specific protocol, only for the DLCI referenced in the Frame-Relay map statement. Mixing Inverse ARP and Frame Relay Map Statements HubCity# show frame-relay map Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 102, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, status defined, active Spokomo# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 211, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO, status defined, active Học viện mạng Bach Khoa - Website: www.bkacad.com 55 • The previous solution worked only because the Inverse ARP had taken place between Spokane and HubCity, and between Spokomo and HubCity, before the Frame-Relay map statements were added. (The Frame-Relay map statement was added after the Inverse ARP took place.) • Both the Inverse-ARP and Frame-Relay map statements are in effect. • Once the router is reloaded (rebooted) the Inverse-ARP will never occur because of the configured Frame-Relay map statement. (assuming the running-config is copied to the startup-config) • Rule: Inverse-ARP will be disabled for that specific protocol, for the DLCI referenced in the Frame-Relay map statement. HubCity# show frame-relay map Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 102, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, status defined, active Spokomo# show frame-relay map Serial0 (up): ip 172.16.1.2 dlci 211, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO, status defined, active Mixing Inverse ARP and Frame Relay Map Statements Học viện mạng Bach Khoa - Website: www.bkacad.com 56 HubCity# show frame-relay map (after reload) Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map NOW MISSING: Serial0 (up): ip 172.16.1.2 dlci 102, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, status defined, active Spokomo# show frame-relay map NOW MISSING: Serial0 (up): ip 172.16.1.2 dlci 211, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO, status defined, active Mixing Inverse ARP and Frame Relay Map Statements Học viện mạng Bach Khoa - Website: www.bkacad.com 57 HubCity# show frame-relay map (after reload) Serial0 (up): ip 172.16.1.1 dlci 101, dynamic, broadcast, status defined, active Serial0 (up): ip 172.16.1.3 dlci 112, dynamic, broadcast, status defined, active Spokane# show frame-relay map Serial0 (up): ip 172.16.1.3 dlci 102, static, CISCO, status defined, active Spokomo# show frame-relay map Serial0 (up): ip 172.16.1.1 dlci 211, static, CISCO, status defined, active Spokane and Spokomo can no longer ping HubCity because they do not have a dlci-to-IP mapping for the other’s IP address! Mixing Inverse ARP and Frame Relay Map Statements Học viện mạng Bach Khoa - Website: www.bkacad.com 58 Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo 172.16.1.1 172.16.1.3 172.16.1.2 DLCI 101 DLCI 102 DLCI 112 DLCI 211 HubCity interface Serial0 ip address 172.16.1.2 255.255.255.0 encapsulation frame-relay (Inverse-ARP still works here) Spokane interface Serial0 ip address 172.16.1.1 255.255.255.0 encapsulation frame-relay frame-relay map ip 172.16.1.3 102 frame-relay map ip 172.16.1.2 102 Spokomo interface Serial0 ip address 172.16.1.3 255.255.255.0 encapsulation frame-relay frame-relay map ip 172.16.1.1 211 frame-relay map ip 172.16.1.2 211 Frame-Relay Map Statements Solution: Do not mix IARP with Frame Relay maps statements. If need be use Frame-Relay map statements instead of IARP. Học viện mạng Bach Khoa - Website: www.bkacad.com 59 Advanced Frame Relay Concepts Học viện mạng Bach Khoa - Website: www.bkacad.com 60 Solving Reachability Issues • By default, a Frame Relay network provides NBMA connectivity between remote sites. NBMA clouds usually use a hub-and-spoke topology. • Unfortunately, a basic routing operation based on the split horizon principle can cause reachability issues on a Frame Relay NBMA network. Học viện mạng Bach Khoa - Website: www.bkacad.com 61 Solving Reachability Issues • To remedy preview situation, turn off split horizon for IP. • When configuring a serial interface for Frame Relay encapsulation, split horizon for IP is automatically turned off. • Of course, with split horizon disabled, the protection it affords against routing loops is lost. • Split horizon is only an issue with distance vector routing protocols like RIP, IGRP and EIGRP. It has no effect on link state routing protocols like OSPF and IS-IS. Router(config-if)#no ip split-horizon [EIGRP {AS_number}] Split Horizon prohibits routing updates received on an interface from exiting that same interface. Học viện mạng Bach Khoa - Website: www.bkacad.com 62 Solving Reachability Issues • Frame Relay can partition a physical interface into multiple virtual interfaces called subinterfaces. • A subinterface is simply a logical interface that is directly associated with a physical interface. Therefore, a Frame Relay subinterface can be configured for each of the PVCs coming into a physical serial interface. Học viện mạng Bach Khoa - Website: www.bkacad.com 63 Solving Reachability Issues • Each point-to-point subnetwork can be assigned a unique network address, which allows packets received on a physical interface to be sent out the same physical interface because the packets are forwarded on VCs in different subinterfaces.This allows each subinterface to act similar to a leased line. • Each point-to-point subinterface is treated as a separate physical interface. Học viện mạng Bach Khoa - Website: www.bkacad.com 64 Key Terminology • Access rate or port speed - This is the clock speed or port speed of the connection or local loop to the Frame Relay cloud. – It is the rate at which data travels into or out of the network, regardless of other settings. • Committed Information Rate (CIR) – This is the rate, in bits per second, at which the Frame Relay switch agrees to transfer data. – The rate is usually averaged over a period of time, referred to as the committed rate measurement interval (Tc). – In general, the duration of Tc is proportional to the "burstiness" of the traffic. Học viện mạng Bach Khoa - Website: www.bkacad.com 65 Key Terminology • Oversubscription – Service providers sometimes sell more capacity than they have on the assumption that not everyone will demand their entitled capacity all of the time. – This oversubscription is analogous to airlines selling more seats than they have in the expectation that some of the booked customers will not show up. per VC Học viện mạng Bach Khoa - Website: www.bkacad.com 66 Bursting • A great advantage of Frame Relay is that any network capacity that is being unused is made available or shared with all customers, usually at no extra charge. • Because the physical circuits of the Frame Relay network are shared between subscribers, there will often be time where there is excess bandwidth available. Frame Relay can allow customers to dynamically access this extra bandwidth and "burst" over their CIR for free. • A device can burst up to the access rate and still expect the data to get through. The duration of a burst transmission should be short, less than 3 or 4 seconds. Học viện mạng Bach Khoa - Website: www.bkacad.com 67 Bursting • Committed Burst Information Rate (CBIR) - The CBIR is a negotiated rate above the CIR which the customer can use to transmit for short burst. It allows traffic to burst to higher speeds, as available network bandwidth permits. However, it cannot exceed the port speed of the link. • Excess Burst Size (BE) is the term used to describe the bandwidth available above the CBIR up to the access rate of the link. Unlike the CBIR, it is not negotiated. Frames may be transmitted at this level but will most likely be dropped. Học viện mạng Bach Khoa - Website: www.bkacad.com 68 Frame Relay Flow Control • Forward Explicit Congestion Notification (FECN) – When a Frame Relay switch recognizes congestion in the network, it sends an FECN packet to the destination device. – This indicates that congestion has occurred. • Backward Explicit Congestion Notification (BECN) – When a Frame Relay switch recognizes congestion in the network, it sends a BECN packet to the source router. – This instructs the router to reduce the rate at which it is sending packets. – With Cisco IOS Release 11.2 or later, Cisco routers can respond to BECN notifications. • The FECN bit, indicated by the "F" in the figure, is set on every frame that the switch receives on the congested link. • The BECN bit, indicated by the "B" in the figure, is set on every frame that the switch places onto the congested link. Học viện mạng Bach Khoa - Website: www.bkacad.com 69 Frame Relay Flow Control • Discard eligibility (DE) bit – When the router or switch detects network congestion, it can mark the packet "Discard Eligible". – The DE bit is set on the traffic that was received after the CIR was met. – These packets are normally delivered. However, in periods of congestion, the Frame Relay switch will drop packets with the DE bit set first. Frame Relay Flow Control • In periods of congestion, the provider's Frame Relay switch applies the following logic rules to each incoming frame based on whether the CIR is exceeded: – If the incoming frame does not exceed the CIBR, the frame is passed. – If an incoming frame exceeds the CIBR, it is marked DE. – If an incoming frame exceeds the CIBR plus the BE, it is discarded. Học viện mạng Bach Khoa - Website: www.bkacad.com 70 Học viện mạng Bach Khoa - Website: www.bkacad.com 71 Frame Relay Flow Control • Frames arriving at a switch are queued or buffered prior to forwarding. As in any queuing system, it is possible that there will be an excessive buildup of frames at a switch. • This causes delays. Delays lead to unnecessary retransmissions that occur when higher level protocols receive no acknowledgment within a set time. In severe cases, this can cause a serious drop in network throughput. To avoid this problem, Frame Relay incorporates a flow control feature. Refer to 3.3.3.1 Frame Relay Flow Control Học viện mạng Bach Khoa - Website: www.bkacad.com 72 Học viện mạng Bach Khoa - Website: www.bkacad.com 73 Frame Relay Flow Control • Activity 3.3.3.2 Học viện mạng Bach Khoa - Website: www.bkacad.com 74 Configuring Advanced Frame Relay Học viện mạng Bach Khoa - Website: www.bkacad.com 75 Configuring Frame Relay Subinterfaces • There are two types of Frame Relay subinterfaces: – Point-to-point – Multipoint Học viện mạng Bach Khoa - Website: www.bkacad.com 76 Configuring Frame Relay Subinterfaces • If the subinterface is configured as point-to-point, the local DLCI for the subinterface must also be configured to distinguish it from the physical interface. • The DLCI is also required for multipoint subinterfaces for which Inverse ARP is enabled. • It is not required for multipoint subinterfaces configured with static route maps. Học viện mạng Bach Khoa - Website: www.bkacad.com 77 • Physical interfaces: With a hub and spoke topology Split Horizon will prevent the hub router from propagating routes learned from one spoke router to another spoke router. • Point-to-point subinterfaces: Each subinterface is on its own subnet. Broadcasts and Split Horizon not a problem because each point-to- point connection is its own subnet. • Multipoint subinterfaces: All participating subinterfaces would be in the same subnet. Broadcasts and routing updates are also subject to the Split Horizon Rule and may pose a problem. Mulitpoint Point-to-point Học viện mạng Bach Khoa - Website: www.bkacad.com 78 Configuring Subinterfaces Example • Step 1. Remove any network layer address assigned to the physical interface. If the physical interface has an address, frames are not received by the local subinterfaces. • Step 2. Configure Frame Relay encapsulation on the physical interface using the encapsulation frame-relay command. • Step 3. For each of the defined PVCs, create a logical subinterface. Specify the port number, followed by a period (.) and the subinterface number. To make troubleshooting easier, it is suggested that the subinterface number matches the DLCI number. • Step 4. Configure an IP address for the interface and set the bandwidth. At this point, we will configure the DLCI. Recall that the Frame Relay service provider assigns the DLCI numbers. • Step 5. Configure the local DLCI on the subinterface using the frame-relay interface-dlci command. Học viện mạng Bach Khoa - Website: www.bkacad.com 79 Configuring Subinterfaces Example Học viện mạng Bach Khoa - Website: www.bkacad.com 80 show frame-relay map • Point-to-point subinterfaces are listed as a “point-to-point dlci” Router#show frame-relay map Serial0.1 (up): point-to-point dlci, dlci 301 (0xCB, 0x30B0), broadcast status defined, active • With multipoint subinterfaces, they are listed as an inverse ARP entry, “dynamic” Router#show frame-relay map Serial0 (up): ip 172.30.2.1 dlci, 301 (0x12D, 0x48D0), dynamic,, broadcast status defined, active Học viện mạng Bach Khoa - Website: www.bkacad.com 81 • Point-to-point subinterfaces are like conventional point-to-point interfaces (PPP, ) and have no concept of (do not need): – Inverse-ARP – mapping of local DLCI address to remote network address (frame-relay map statements) • Frame-Relay service supplies multiple PVCs over a single physical interface and point-to-point subinterfaces subdivide each PVC as if it were a physical point-to-point interface. • Point-to-point subinterfaces completely bypass the local DLCI to remote network address mapping issue. Point-to-point Subinterfaces Mulitpoint Point-to-point Học viện mạng Bach Khoa - Website: www.bkacad.com 82 • With point-to-point subinterfaces you: – Cannot have multiple DLCIs associated with a single point-to- point subinterface – Cannot use frame-relay map statements – Cannot use Inverse-ARP – Can use the frame-relay interface dlci statement (for both point-to-point and multipoint) Point-to-point Subinterfaces Mulitpoint Point-to-point Học viện mạng Bach Khoa - Website: www.bkacad.com 83 172.30.1.0/24 172.30.2.0/24 172.30.3.0/24 Each subinterface is on a separate network or subnet with a single remote router at the other end of the PVC. Point-to-point Subinterfaces Học viện mạng Bach Khoa - Website: www.bkacad.com 84 • Point-to-point subinterfaces are equivalent to using multiple physical “point to point” interfaces. S0 S1 S2 Site A Site B Site C 172.30.1.1/24 172.30.2.1/24 172.30.3.1/24 172.30.1.2/24 172.30.2.2/24 172.30.3.2/24 Học viện mạng Bach Khoa - Website: www.bkacad.com 85 • A single subinterface is used to establish one PVC connection to another physical or subinterface on a remote router. • In this case, the interfaces would be: – In the same subnet – Each interface would have a single DLCI • Each point-to-point connection is its own subnet. • In this environment, broadcasts are not a problem because the routers are point-to-point and act like a leased line. Point-to-point Subinterfaces Học viện mạng Bach Khoa - Website: www.bkacad.com 86 • Point-to-point subinterface configuration, minimum of two commands: Router(config)# interface Serial0.1 point-to-point Router(config-subif)# frame-relay interface-dlci dlci • Rules: 1. No Frame-Relay map statements can be used with point-to-point subinterfaces. 2. One and only one DLCI can be associated with a single point-to-point subinterface • By the way, encapsulation is done only at the physical interface: interface Serial0 no ip address encapsulation frame-relay Point-to-point Subinterfaces Học viện mạng Bach Khoa - Website: www.bkacad.com 87 Point-to-Point Subinterfaces at the Hub and Spokes Each subinterface on Hub router requires a separate subnet (or network) • Each subinterface on Hub router is treated like a regular physical point-to-point interface, so split horizon does not need to be disabled. Interface Serial0 (for all routers) encapsulation frame-relay no ip address HubCity interface Serial0.1 point-to-point ip address 172.16.1.1 255.255.255.0 encapsulation frame-relay frame-relay interface dlci 301 interface Serial0.2 point-to-point ip address 172.16.2.1 255.255.255.0 encapsulation frame-relay frame-relay interface dlci 302 Spokane interface Serial0.1 point-to-point ip address 172.16.1.2 255.255.255.0 frame-relay interface dlci 103 Spokomo interface Serial0.1 point-to-point ip address 172.16.2.2 255.255.255.0 frame-relay interface dlci 203 Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo Serial 0.1 172.16.1.2/24 Serial 0.1 172.16.2.2/24 Serial 0.1 172.16.1.1/24 DLCI 301 DLCI 103 DLCI 302 DLCI 203 Serial 0.2 172.16.2.1/24 Two subnets Học viện mạng Bach Khoa - Website: www.bkacad.com 88 • Share many of the same characteristics as a physical Frame-Relay interface • With multipoint subinterface you: – can have multiple DLCIs assigned to it. – can use frame-relay map & interface dlci statements – can use Inverse-ARP • Remember, with point-to-point subinterfaces you: – cannot have multiple DLCIs associated with a single point-to-point subinterface – cannot use frame-relay map statements – cannot use Inverse-ARP – (can use the frame-relay interface dlci statement for both point-to-point and multipoint) Mulitpoint Point-to-point Multipoint Subinterfaces • interface Serial0/0/0 • no ip address • encapsulation frame-relay • interface Serial0/0/0.1 multipoint • ip address 172.16.1.1 255.255.255.0 • no ip split-horizon • frame-relay interface-dlci 103 • frame-relay interface-dlci 102 Học viện mạng Bach Khoa - Website: www.bkacad.com 89 • interface Serial0/0/0.2 point-to-point • ip address 172.16.2.1 255.255.255.0 • frame-relay interface-dlci 102 • ! • interface Serial0/0/0.3 point-to-point • ip address 172.16.1.1 255.255.255.0 • frame-relay interface-dlci 103 Học viện mạng Bach Khoa - Website: www.bkacad.com 90 • R3-SP1(config-if)#frame-relay lmi-type ansi Học viện mạng Bach Khoa - Website: www.bkacad.com 91 Học viện mạng Bach Khoa - Website: www.bkacad.com 92 Multipoint subinterfaces 172.30.1.0/24 172.30.2.0/24 172.30.3.0/24 Each subinterface is on a separate network or subnet but may have multiple connections, with a different DLCI for each connection. Split horizon still an issue on each Multipoint subinterface. Học viện mạng Bach Khoa - Website: www.bkacad.com 93 • Multipoint subinterfaces are equivalent to using multiple physical “hub to spoke” interfaces. S0 S1 S2 Site A1 Site B1 Site C2 172.30.1.1/24 172.30.2.1/24 172.30.3.1/24 172.30.1.2/24 172.30.2.2/24 172.30.3.3/24 Site A2 172.30.1.3/24 Site B2 172.30.2.3/24 Site C1 172.30.3.2/24 Học viện mạng Bach Khoa - Website: www.bkacad.com 94 Frame Relay Network Headquarters Hub City Satellite Office 1 Spokane Satellite Office 2 Spokomo Serial 0 172.16.3.1 Serial 0 172.16.3.2 Serial 0 172.16.3.3 DLCI 301 DLCI 103 DLCI 302 DLCI 203 Notes • Highly scalable solution • Disable Split Horizon on Hub router when running a distance vector routing protocol Interface Serial0 (for all routers) encapsulation frame-relay no ip address HubCity interface Serial0.1 mulitpoint ip address 172.16.3.3 255.255.255.0 frame-relay interface-dlci 301 frame-relay interface-dlci 302 no ip split-horizon [EIGRP {AS_number}] Spokane interface Serial0.1 point-to-point ip address 172.16.3.1 255.255.255.0 frame-relay interface-dlci 103 Spokomo interface Serial0.1 point-to-point ip address 172.16.3.2 255.255.255.0 frame-relay interface-dlci 203 Multipoint subinterface at the Hub and Point-to-Point Subinterfaces at the Spokes One subnet Học viện mạng Bach Khoa - Website: www.bkacad.com 95 Verifying Frame Relay Operation Học viện mạng Bach Khoa - Website: www.bkacad.com 96 Verifying Frame Relay Operation Học viện mạng Bach Khoa - Website: www.bkacad.com 97 Verifying Frame Relay Operation Học viện mạng Bach Khoa - Website: www.bkacad.com 98 Verifying Frame Relay Operation Học viện mạng Bach Khoa - Website: www.bkacad.com 99 Verifying Frame Relay Operation Học viện mạng Bach Khoa - Website: www.bkacad.com 100 Troubleshooting Frame Relay Configuration Học viện mạng Bach Khoa - Website: www.bkacad.com 101 Troubleshooting Frame Relay Configuration Học viện mạng Bach Khoa - Website: www.bkacad.com 102 Troubleshooting Frame Relay Configuration • When an Inverse ARP request is made, the router updates its map table with three possible LMI connection states. These states are active state, inactive state, and deleted state – ACTIVE States indicates a successful end-to-end (DTE to DTE) circuit. – INACTIVE State indicates a successful connection to the switch (DTE to DCE) without a DTE detected on the other end of the PVC. This can occur due to residual or incorrect configuration on the switch. – DELETED State indicates that the DTE is configured for a DLCI the switch does not recognize as valid for that interface. Học viện mạng Bach Khoa - Website: www.bkacad.com 103 Troubleshooting Frame Relay Configuration • The possible values of the status field are as follows: – 0x0 - The switch has this DLCI programmed, but for some reason it is not usable. The reason could possibly be the other end of the PVC is down. – 0x2 - The Frame Relay switch has the DLCI and everything is operational. – 0x4 - The Frame Relay switch does not have this DLCI programmed for the router, but that it was programmed at some point in the past. This could also be caused by the DLCIs being reversed on the router, or by the PVC being deleted by the service provider in the Frame Relay cloud. Học viện mạng Bach Khoa - Website: www.bkacad.com 104 Troubleshooting Frame Relay Configuration Học viện mạng Bach Khoa - Website: www.bkacad.com 105 Extra: Configure a Router as a FR Switch • Enable frame-relay switching on the router acting as the service provider Frame Relay cloud as follows: FRswitch(config)#frame-relay switching Học viện mạng Bach Khoa - Website: www.bkacad.com 106 Extra: Configure a Router as a FR Switch • The remaining configurations on the Frame Relay switch are specific to the interfaces. On each serial interface, configure the encapsulation to Frame Relay, define the interface as a Frame Relay DCE, and set the clockrate (if the serial interface connects to DCE cable). • The following is an example: FRswitch(config-if)#encapsulation frame-relay FRswitch(config-if)#frame-relay intf-type dce FRswitch(config-if)#clock rate 56000 Học viện mạng Bach Khoa - Website: www.bkacad.com 107 Extra: Configure a Router as a FR Switch • Frame Relay switches identify inbound frames by their data-link connection identifier (DLCI). The DLCI is then referenced in a switching table to determine the outbound port. • Statically define an end-to-end PVC between SanJose1 and London. A static route needs to be configured for each serial interface, as shown in the following: FRswitch(config)#interface serial 0/0 FRswitch(config-if)#frame-relay route 102 interface serial 0/1 201 FRswitch(config-if)#interface serial 0/1 FRswitch(config-if)#frame-relay route 201 interface serial 0/0 102 Học viện mạng Bach Khoa - Website: www.bkacad.com 108 Extra: Configure a Router as a FR Switch • FRswitch(config)#frame-relay switching Học viện mạng Bach Khoa - Website: www.bkacad.com 109 Extra: Configure a Router as a FR Switch FRswitch(config)#interface serial 0/0 FRswitch(config-if)#encapsulation frame-relay {cisco | ietf } FRswitch(config-if)#frame-relay intf-type dce FRswitch(config-if)#clock rate 56000 // option FRswitch(config-if)#frame-relay route 102 interface serial 0/1 201 FRswitch(config-if)#frame-relay lmi-type {cisco|ansi|q933a} //option Học viện mạng Bach Khoa - Website: www.bkacad.com 110 Extra: Configure a Router as a FR Switch FRswitch(config)#interface serial 0/1 FRswitch(config-if)#encapsulation frame-relay {cisco | ietf} FRswitch(config-if)#frame-relay intf-type dce FRswitch(config-if)#clock rate 56000 // option FRswitch(config-if)#frame-relay route 201 interface serial 0/0 102 FRswitch(config-if)#frame-relay lmi-type {cisco|ansi|q933a} //option Học viện mạng Bach Khoa - Website: www.bkacad.com 111 Extra: Configure a Router as a FR Switch • Verifying: HUB • interface Serial0/0/0 • no ip address • encapsulation frame-relay • ! • interface Serial0/0/0.1 multipoint • ip address 192.168.1.4 255.255.255.0 • no ip split-horizon • frame-relay interface-dlci 401 • frame-relay interface-dlci 402 • ! • interface Serial0/0/0.2 point-to-point • ip address 192.168.2.4 255.255.255.0 • frame-relay interface-dlci 403Học viện mạng Bach Khoa - Website: www.bkacad.com 112 SP1 • interface Serial0/0/0 • no ip address • encapsulation frame-relay • ! • interface Serial0/0/0.1 point-to-point • ip address 192.168.1.1 255.255.255.0 • frame-relay interface-dlci 104 Học viện mạng Bach Khoa - Website: www.bkacad.com 113 Học viện mạng Bach Khoa - Website: www.bkacad.com 114 Labs Học viện mạng Bach Khoa - Website: www.bkacad.com 115 Summary Học viện mạng Bach Khoa - Website: www.bkacad.com 116