Some IOS default settings when configuring Frame Relay:

• LMI tyep is automatically sensed
• Encapsulation is Cisco (vs. IETF)
• DLCIs of the PVCs are learned via LMI status messages
• Inverse ARP is enabled

The most basic Frame Relay command that tells the routers to use Frame Relay dat-link protocols instead of the default HDLC:

#encapsulation frame-relay

If another router is not Cisco, you must use IETF encapsulation:

#encapsulation frame-relay ieft

The encapsulation command applies to all VCs on that interface.

If a change of LMI is necessary, configure the physical interface for the router as:

#frame-relay lmi-type ansi | q933a

Note: The LMI setting is a per-physical-interface setting, even if subinterfaces are used.

Frame Relay Address Mapping

• Frame Relay mapping “maps” a Layer 3 (IP) address and its corresponding Layer 2 (DLCI) address
• Inverse Arp
  • dynamically creates a mapping between the Layer 3 address and the Layer 2 address.
  • As soon as the LMI signals the VC is up, Inverse ARP learns the DLCI of its VCs, then it announces its own Layer 3 address.
  • To see the result of the inverse arp, use the following command to see the Frame Relay map table:

#show frame-relay map

• Static Frame Relay Mapping
  • Instead of using Inverse Arp, manually configuring static maps is possible:

#no frame-relay inverse-arp
#frame-relay map ip 199.1.1.2 52 broadcast

• • • The IP address 199.1.1.2 in the example is the IP address of the next-hop router
    • “52″ is the DLCI used to reach the router with the 199.1.1.2 ip address.
    • “broadcast” keyword allows the routers to send broadcasts or multicasts to neighboring router – for routing protocols such as RIP, OSPF, EIGRP, etc.
    • the “no frame-relay inverse arp” obviously means no frame-relay inverse arp!

Point-to-point Configuration

R1(config)#interface s0/0/0
R1(config-if)#encapsulation frame-relay

R1(config-if)#interface s0/0/0.1 point-to-point
R1(config-subif)#ip address 140.1.1.1 255.255.255.0
R1(config-subif)#frame-relay interface-dlci 52

R1(config-fr-dlci)#interface s0/0/0.2 point-to-point
R1(config-subif)#ip address 140.1.2.1 255.255.255.0
R1(config-subif)#frame-relay interface-dlci 53

R1(config-fr-dlci)#interface s0/0/0.3 point-to-point
R1(config-subif)#ip address 140.1.3.1 255.255.255.0
R1(config-subif)#frame-relay interface dlci 53

• The interface s0/0/0.1 point-to-point command creates logical subinterface number 1 under physical interface s0/0/0.
  • the subinterface numbers do not have to match on the router on the other end of the PVC, nor does the DLCI number.
• The frame-relay interface-dlci subinterface command tells the router which single DLCI is associated with that subinterface
  • associates the correct PVC with the subinterface
  • an alternative command to use in place of this is frame-relay map command. For example, frame-relay map ip 140.1.1.2 52 broadcast .
    • if frame-relay map command is used, Inverse ARP is disabled. Therefore the router on the other end of the VC will nor receive any Inverse ARP messages and may need to be configured with the frame-relay map command as well.

Global and Local Addressing (as pertains to the CCNA exam

• For three or more routers in a diagram, if it shows a main site with 3 PVCs, one to each remote site:
  • If only one DLCI is shown beside the main site router, it implies the use of global addressing.
  • If the diagram shows a DLCI for each PVC beside the main site router, it is using local DLCI
• If there are only 2 routers, you need to read into the question, answers, or any configuration.
  • On any given router, only local DLCI values are in the configuration or show commands.

Frame Relay Verification

• #show frame-relay pvc
  • lists useful management information such as:
    • packet counters for each VC
    • counters for FECN and BECN
    • shows PVC status
    • comparison of packets/bytes sent on one router vs. counters on packets received on the router on the other end of the VC.
• #show frame-relay map
  • lists mapping information:
    • for example, for fully meshed network in which the configuration did not use any subinterfaces, a Layer 3 address is listed with each DLCI
    • for instances where subinterfaces are used on a point-to-point network, there is no Layer 3 address shown.
      • subinterfaces require the use of frame-relay interface-dlci command.
      • Inverse ARP or static frame-relay map statements is needed only when more than two VCs terminate on the interface or subinterface, because those are instances in which confusion over which DLCI to use might occur.
• #debug frame-relay lmi
  • Lists information for the sending and receiving LMI inquiries.
  • The switch sends the status message.
  • The DTE (router) sends the status inquiry.
  • Cisco default is to send, and expect to receive theses status messages.
  • no keepalive command is used to disable the use of LMI status messages.
  • Unlike other interfaces, Cisco keepalive messages do not flow from router to router over Frame Relay. Instead, they are simply used to detect whether the router has connectivity to its local Frame Relay switch.

Hybrid Network

R1(config)#interface s0/0/0
R1(config-if)#encapsulation frame-relay

R1(config-if)#interface s0/0/0.1 multipoint
R1(config-subif)#ip address 140.1.1.1 255.255.255.0
R1(config-subif)#frame-relay interface-dlci 502
R1(config-subif)#frame-relay interface-dlci 503

R1(config-fr-dlci)#interface s0/0/0.2 point-to-point
R1(config-subif)#ip address 140.1.2.1 255.255.255.0
R1(config-subif)#frame-relay interface-dlci 504

R1(config-fr-dlci)#interface s0/0/0.3 point-to-point
R1(config-subif)#ip address 140.1.3.1 255.255.255.0
R1(config-subif)#frame-relay interface dlci 505

R2(config)#interface s0/0/0
R2(config-if)#encapsulation frame-relay

R2(config-if)#interface s0/0/0.1 multipoint
R2(config-subif)#ip address 140.1.1.2 255.255.255.0
R2(config-subif)#frame-relay interface-dlci 501
R2(config-subif)#frame-relay interface-dlci 503

R3(config)#interface s0/0/0
R3(config-if)#encapsulation frame-relay

R3(config-if)#interface s0/0/0.1 multipoint
R3(config-subif)#ip address 140.1.1.3 255.255.255.0
R3(config-subif)#frame-relay interface-dlci 501
R3(config-subif)#frame-relay interface-dlci 502

R4(config)#interface s0/0/0
R4(config-if)#encapsulation frame-relay

R4(config-if)#interface s0/0/0.1 point-to-point
R4(config-subif)#ip address 140.1.2.4 255.255.255.0
R4(config-subif)#frame-relay interface-dlci 501

R5(config)#interface s0/0/0
R5(config-if)#encapsulation frame-relay

R5(config-if)#interface s0/0/0.1 point-to-point
R5(config-subif)#ip address 140.1.3.5 255.255.255.0
R5(config-subif)#frame-relay interface-dlci 501

• Multipoint
  • Multipoint means there is more than one VC. That means you can send and receive to and from more than one VC on the subinterface.
  • Multipoint subinterfaces work best on a full mesh network.
  • Like point-to-point subinterfaces, you use the frame-relay interface-dlci x command to configure it.
  • On the diagram above, R1 configures s0/0/0.1 subinterface as a multipoint and lists DLCIs for R2 and R3.
    • Whereas on the point-to-point interfaces s0/0/0.2 and s0/0/0.3, only a single DLCI (for the one PVC connected to each) is configured.
    • In fact only one frame-relay interface-dlci command is allowed on a point-to-point subinterface because only one VC is allowed.
  • Mapping Statements:
    • Multipoint subinterfaces – non are required because Inverse ARP is enabled by default on multipoint subinterfaces.
    • Point-to-point – no mapping is ever needed because the only DLCI associated with the interface is statically configured with the frame-relay interface-dlci command.
  • show frame-relay map
    • The output of the show frame-relay map will show the mapping information learned by Inverse ARP on the multipoint subinterfaces.
    • The output will show Layer 3 information because there are more than one DLCI associated with a multipoint interface therefore the router needs the mapping information to match the next-hop IP address to the correct DLCI.