Troubleshooting Frame Relay

This section discusses troubleshooting procedures for connectivity problems related to Frame Relay links. It describes specific Frame Relay symptoms, the problems that are likely to cause each symptom, and the solutions to those problems.

The following sections cover the most common network issues in Frame Relay networks:

•Frame Relay: Frame Relay Link Is Down

•Frame Relay: Cannot ping Remote Router

•Frame Relay: Cannot ping End to End

Frame Relay: Frame Relay Link Is Down

Symptom: Connections over a Frame Relay link fail. The output of the show interfaces serial exec command shows that the interface and line protocol are down, or that the interface is up and the line protocol is down.

Table 18-1 outlines the problems that might cause this symptom and describes solutions to those problems.

Table 18-1 Frame Relay: Frame Relay Link Is Down 

Possible Problem	Solution
A cabling, hardware, or carrier problem has occurred.	Perform these steps for the local and remote router: 1. Use the show interfaces serial command to see whether the interface and line protocol are up. 2. If the interface and line protocol are down, check the cable to make sure that it is a DTE1 serial cable. Make sure that cables are securely attached. 3. If the cable is correct, try moving it to a different port. If that port works, then the first port is defective. Replace either the card or the router. 4. If the cable doesn't work on the second port, try replacing the cable. If it still doesn't work, there might be a problem with the DCE2 . Contact your carrier about the problem. For detailed information on troubleshooting serial lines, refer to Chapter 15, "Troubleshooting Serial Lines."
An LMI3 type mismatch has occurred.	1. Use the show interfaces serial command to check the state of the interface. 2. If the output shows that the interface is up but the line protocol is down, use the show frame-relay lmi exec command to see which LMI type is configured on the Frame Relay interface. 3. Make sure that the LMI type is the same for all devices in the path from source to destination. Use the frame-relay lmi-type {ansi | cisco | q933a} interface configuration command to change the LMI type on the router.
Keepalives are not being sent.	1. Enter the show interfaces command to find out whether keepalives are configured. If you see a line that says "keepalives not set," keepalives are not configured. 2. Use the keepalive seconds interface configuration command to configure keepalives. The default value for this command is 10 seconds.
Encapsulation mismatch has occurred.	1. When connecting Cisco devices with non-Cisco devices, you must use IETF4 encapsulation on both devices. Check the encapsulation type on the Cisco device with the show frame-relay map exec command. 2. If the Cisco device is not using IETF encapsulation, use the encapsulation frame-relay ietf interface configuration command to configure IETF encapsulation on the Cisco Frame Relay interface. For information on viewing or changing the configuration of the non-Cisco device, refer to the vendor documentation.
The DLCI5 is inactive or has been deleted.	1. Use the show frame-relay pvc exec command to view the status of the interface's PVC. 2. If the output shows that the PVC6 is inactive or deleted, there is a problem along the path to the remote router. Check the remote router or contact your carrier to check the status of the PVC.
The DLCI is assigned to the wrong subinterface.	1. Use the show frame-relay pvc privileged exec command to check the assigned DLCIs. Make sure that the correct DLCIs are assigned to the correct subinterface. If the DLCI is incorrect, use the no frame-relay map interface-dlci command to delete the incorrect DLCI number entry under the interface. Use the frame-relay map interface-dlci interface configuration command to define the mapping between an address and the correct DLCI used to connect to the address. Syntax: frame-relay map protocol protocol-address dlci [broadcast] [ietf | cisco] Syntax description: •protocol—Supported protocols: AppleTalk, DECnet, IP, XNS, IPX, and VINES. •protocol-address—Address for the protocol. •dlci—DLCI number for the interface. •broadcast—(Optional) Broadcasts should be forwarded to this address when multicast is not enabled. •ietf—(Optional) IETF form of Frame Relay encapsulation. Use when the communication server is connected to another vendor's equipment across a Frame Relay network. •cisco—(Optional) Cisco encapsulation method. Example: The following example maps IP address 131.108.123.1 to DLCI 100: interface serial 0 frame-relay map ip 131.108.123.1 100 broadcast 2. If the DLCIs appear to be correct, shut down the main interface using the shutdown interface configuration command, and then bring the interface back up using the no shutdown command.

1 DTE = data terminal equipment 2 DCE = data circuit-terminating equipment 3 LMI = Local Management Interface 4 IETF = Internet Engineering Task Force 5 DLCI = Data link connection identifier 6 PVC = permanent virtual circuit

Frame Relay: Cannot ping Remote Router

Symptom: Attempts to ping the remote router across a Frame Relay connection fail.

Table 18-2 outlines the problems that might cause this symptom and describes solutions to those problems.

Table 18-2 Frame Relay: Cannot ping Remote Router 

Possible Problem	Solution
Encapsulation mismatch has occurred.	1. When connecting Cisco devices with non-Cisco devices, you must use IETF encapsulation on both devices. Check the encapsulation type on the Cisco device with the show frame-relay map exec command. 2. If the Cisco device is not using IETF encapsulation, use the encapsulation frame-relay ietf interface configuration command to configure IETF encapsulation on the Cisco Frame Relay interface. For information on viewing or changing the configuration of the non-Cisco device, refer to the vendor documentation.
DLCI is inactive or has been deleted.	1. Use the show frame-relay pvc exec command to view the status of the interface's PVC. 2. If the output shows that the PVC is inactive or deleted, there is a problem along the path to the remote router. Check the remote router, or contact your carrier to check the status of the PVC.
DLCI is assigned to the wrong subinterface.	1. Use the show frame-relay pvc privileged exec command to check the assigned DLCIs. Make sure that the correct DLCIs are assigned to the correct subinterfaces. 2. If the DLCIs appear to be correct, shut down the main interface using the shutdown interface configuration command, and then bring the interface back up using the no shutdown command.
An access list was misconfigured.	1. Use the show access-list privileged exec command to see whether there are access lists configured on the router. 2. If there are access lists configured, test connectivity by disabling access lists using the no access-group global configuration command. Check whether connectivity is restored. 3. If connections work, re-enable access lists one at a time, checking connections after enabling each access list. 4. If enabling an access list blocks connections, make sure that the access list does not deny necessary traffic. Make sure to configure explicit permit statements for any traffic that you want to pass. 5. Continue testing access lists until all access lists are restored and connections still work.
The frame-relay map command is missing.	1. Use the show frame-relay map privileged exec command to see whether an address map is configured for the DLCI. 2. If you do not see an address map for the DLCI, enter the clear frame-relay-inarp privileged exec command and then use the show frame-relay map command again to see whether there is now a map to the DLCI. 3. If there is no map to the DLCI, add a static address map. Use the frame-relay map interface configuration command. Syntax: •frame-relay map protocol protocol-address dlci [broadcast] [ietf | cisco] Syntax Description: •protocol—Supported protocols: AppleTalk, DECnet, IP, XNS, IPX, and VINES. •protocol-address—Address for the protocol. •dlci—DLCI number for the interface. •broadcast—(Optional) Broadcasts should be forwarded to this address when multicast is not enabled. •ietf—(Optional) IETF form of Frame Relay encapsulation. Use when the communication server is connected to another vendor's equipment across a Frame Relay network. •cisco—(Optional) Cisco encapsulation method. Example: The following example maps IP address 131.108.123.1 to DLCI 100: interface serial 0 frame-relay map ip 131.108.123.1 100 broadcast 4. Make sure that the DLCIs and next-hop addresses specified in frame-relay map commands are correct. The specified protocol address should be in the same network as your local Frame Relay interface. For complete information on configuring Frame Relay address maps, refer to the Cisco IOS Wide-Area Networking Configuration Guide.
No broadcast keyword is found in frame-relay map statements.	1. Use the show running-config privileged exec command on local and remote routers to view the router configuration. Check frame-relay map command entries to see whether the broadcast keyword is specified. 2. If the keyword is not specified, add the broadcast keyword to all frame-relay map commands. Syntax: frame-relay map protocol protocol-address dlci [broadcast] [ietf | cisco] Syntax Description: •protocol—Supported protocols: AppleTalk, DECnet, IP, XNS, IPX, and VINES. •protocol-address—Address for the protocol. •dlci—DLCI number for the interface. •broadcast—(Optional) Broadcasts should be forwarded to this address when multicast is not enabled. •ietf—(Optional) IETF form of Frame Relay encapsulation. Use when the communication server is connected to another vendor's equipment across a Frame Relay network. •cisco—(Optional) Cisco encapsulation method. Example: The following example maps IP address 131.108.123.1 to DLCI 100: interface serial 0 frame-relay map ip 131.108.123.1 100 broadcast Note: By default, the broadcast keyword is added to dynamic maps learned via Inverse ARP1 .

1 ARP = Address Resolution Protocol

Frame Relay: Cannot ping End to End

Symptom: Attempts to ping devices on a remote network across a Frame Relay connection fail.

Table 18-3 outlines the problems that might cause this symptom and describes solutions to those problems.

Table 18-3 Frame Relay: Cannot ping End to End

Possible Problem	Solution
Split horizon problem	In a hub-and-spoke Frame Relay environment, you must configure subinterfaces to avoid problems with split horizon. For detailed information on configuring subinterfaces, refer to the Cisco IOS Wide-Area Networking Configuration Guide and Wide-Area Networking Command Reference. Frame Relay subinterfaces provide a mechanism for supporting partially meshed Frame Relay networks. Most protocols assume transitivity on a logical network; that is, if station A can talk to station B, and station B can talk to station C, then station A should be capable of talking to station C directly. Transitivity is true on LANs, but not on Frame Relay networks, unless A is directly connected to C. Additionally, certain protocols such as AppleTalk and transparent bridging cannot be supported on partially meshed networks because they require split horizon, in which a packet received on an interface cannot be transmitted out the same interface even if the packet is received and transmitted on different virtual circuits. Configuring Frame Relay subinterfaces ensures that a single physical interface is treated as multiple virtual interfaces. This capability enables us to overcome split horizon rules. Packets received on one virtual interface can now be forwarded out another virtual interface, even if they are configured on the same physical interface. Subinterfaces address the limitations of Frame Relay networks by providing a way to subdivide a partially meshed Frame Relay network into a number of smaller, fully meshed (or point-to-point) subnetworks. Each subnetwork is assigned its own network number and appears to the protocols as if it is reachable through a separate interface. (Note that point-to-point subinterfaces can be unnumbered for use with IP, reducing the addressing burden that might otherwise result.)
No default gateway on workstation	1. From the local workstation or server, try to ping the remote workstation or server. Make several attempts to ping the remote device if the first ping is unsuccessful. 2. If all your attempts fail, check whether the local workstation or server can ping the local router's Frame Relay interface. 3. If you are unable to ping the local interface, check the local workstation or server to see whether it is configured with a default gateway specification. 4. If no default gateway is specified, configure the device with a default gateway. The default gateway should be the address of the local router's LAN interface. For information on viewing or changing the workstation or server's default gateway specification, refer to the vendor documentation.

3. Configure frame-relay
3.1 Configure FR Switch as a Frame Relay switch and create a PVC between R1 and R2
FR-Switch(config)# frame-relay switching
FR-Switch(config)# interface serial 0/0/0
FR-Switch(config)# clock rate 64000
FR-Switch(config-if)# encapsulation frame-relay
FR-Switch(config-if)# frame-relay intf-type dce
FR-Switch(config-if)# frame-relay route 102 interface serial 0/0/1 201
FR-Switch(config-if)# interface serial 0/0/1
FR-Switch(config-if)# clock rate 64000
FR-Switch(config-if)# encapsulation frame-relay
FR-Switch(config-if)# frame-relay intf-type dce
FR-Switch(config-if)# frame-relay route 201 interface serial 0/0/0 102
FR-Switch(config-if)# no shutdown

FR-Switch# show frame-relay pvc
FR-Switch# show frame-relay route

R1(config)# interface serial 0/0/1
R1(config-if)# encapsulation frame-relay
R1(config-if)# no frame-relay inverse-arp
R1(config-if)# frame-relay map ip 10.1.1.2 102 broadcast
R1(config-if)# no shutdown


R2(config)# interface serial 0/0/0
R2(config-if)# encapsulation frame-relay
R2(config-if)# no frame-relay inverse-arp
R2(config-if)# frame-relay map ip 10.1.1.1 201 broadcast
R1(config-if)# no shutdown

DLCI stand for?
show frame-relay pvc
show frame-relay route]
show ip route
show ip route

4. Verify the configuration
4.1 ping from R1 to R2 and from R2 to R1
4.2 Get PVC information
R1#show frame-relay pvc
R2#show frame-rely pvc
FR Switch#show frame-relay pvc
4.3 Verify Frame Relay mappings
R1# show frame-relay map
R2# show frame-relay map
FR switch: none
4.4 Debug the Frame Relay LMI
R1# debug frame-relay lmi

5. Troubleshooting Frame Relay
5.1 Remove the frame-relay map from R1
R1# configure terminal
R1(config)# interface serial 0/0/1
R1(config-if)# encapsulation frame-relay
R1(config-if)# no frame-relay map ip 10.1.1.2 102 broadcast

5.2 ping R1 dari R2 (Ping ke yang tidak ada frame-relay map ip nya)
R2# ping 10.1.1.1
Ping should be failed

5.3 Issue the debug ip icmp command on R1(Router yang tidak ada frame-relay map ip nya)
R1# debug ip icmp

5.4 Ping R1 dari R2
R2# ping 10.1.1.1

5.5
As is shown by this debug message, the ICMP packet from R2 is reaching R1.

5.6 Issuing the show frame-relay map command
R1# show frame-relay map

6. Change the Frame Relay encapsulation type
6.1 Change the frame relay encapsulation on serial0/0/1 on R2 to IETF (Notice: interface that goes to router R1)
R2(config-if)# encapsulation frame-relay ietf
Notice:
1. no EIGRP break-up
2. FR Switch dan R2 still passing traffic

6.1 Change the encapsulation type back to the default:
R2(config-if)# encapsulation frame-relay

7. Change the LMI type
7.1 On R2
R2# configure terminal
R2(config)# interface serial 0/0/1
R2(config-if)# encapsulation frame-relay
R2(config-if)# frame-relay lmi-type ansi
R2(config-if)# ^Z
R2# copy run start

7.2 Show interface on R2
Serial0/0/1 is up, line protocol is down

7.3 Show frame-relay lmi on R2
R2# show frame-relay lmi

7.4 Issue debug frame-relay lmi command on R2. Notice that LMI packets are no longer showing up in pairs.
R2# debug frame-relay lmi

7.5 Leave debugging on and restore the LMI type to Cisco on R2
R2(config-if)# frame-relay lmi-type cisco


8. Configure frame-relay and subinterfaces
a. point-to-point sub interfaces
b. point-to-multipoint subinterfaces. Point-to-point

8.1 On FR switch, create a new PVC between R1 and R2
FR-Switch(config)# interface serial 0/0
FR-Switch(config-if)# frame-relay route 112 interface serial 0/0/1 212
FR-Switch(config-if)# interface serial0/0/1
FR-Switch(config-if)# frame-relay route 212 interface serial0/0/0 112

8.2 Create and configure a point-to-point subinterface on R1
Create subinterface 112 as a point-to-point interface. Frame Relay encapsulation must be specified on the physical interface before subinterface can be created:
R1(config)# interface serial 0/0/1.112 point-to-point
R1(config-if)# ip address 10.1.1.5 255.255.255.252
R1(config-if)# frame-relay interface-dlci 112

8.3 Create and configure a point-to-point sub-interface on R2
R2(config)# interface serial 0/0/1.212 point-to-point
R2(config-if)# ip address 10.1.1.6 255.255.255.252
R2(config-subif)# frame-relay interface-dlci 212

8.4 Verify connectivity
8.4.1 Ping R2 dari R1
R1# ping 10.1.1.6
R2# ping 10.1.1.5

R1# show frame-relay pvc
R2# show frame-relay pvc
FR-Switch# show frame-relay pvc

R1# show frame-relay map
R2# show frame-relay map
FR-Switch# show frame-relay route

8.5 Debug the frame-relay LMI