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Document ID: 7925
Contents
Introduction
Prerequisites
Requirements
Components Used
Conventions
Configure
Network Diagram
Configurations
Verify
Troubleshoot
Related Information
Introduction
This document provides a sample configuration for Link Access Procedure, Balanced (LAPB) back-to-back connections. You can use it to verify that your connections and hardware are working properly.
Prerequisites
Requirements
There are no specific prerequisites for this document.
Components Used
The information in this document is based on the software and hardware versions below.
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The DCE side is connected with a WAN DCE cable.
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The DTE side is connected with a WAN DTE cable.
Note: For more information on WAN DCE and DTE cables please refer to the Serial Cables documentation.
The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.
Conventions
For more information on document conventions, see the Cisco Technical Tips Conventions.
Configure
In this section, you are presented with the information to configure the features described in this document.
The default serial encapsulation on Cisco routers is High-Level Data Link Control (HDLC). You must explicitly configure an LAPB encapsulation using the command encapsulation lapb. The keyword 'dce' at the end of this command specifies operation as a data communications equipment (DCE) device.
With a back-to-back serial connection, the router connected to the DCE end of the cable provides the clock signal for the serial link. The clockrate command in the interface configuration mode enables the router at the DCE end (Prasit, in this example) of the cable to provide clock signal for the serial link.Use the show controllers command to see which end of the cable is connected to the serial interface. In this example, the DCE end of the cable is connected to Prasit (hence the clockrate command) and DTE end to Spicey.
Note: Any of the routers can act as logical DCE device, irrespective of which end of the cable it is connected to. For instance, the command encapsulation lapb dce can be placed under the serial interface of either one of the above two routers. In the given example, Prasit is acting as the LAPB DCE device.
For more information on the LAPB encapsulation, please refer to the Command Reference Guide.
Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .
Network Diagram
This document uses the network setup shown in the diagram below.
Configurations
This document uses the configurations shown below.
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Prasit |
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interface Serial0 ip address 5.0.2.1 255.255.255.0 encapsulation lapb dce clockrate 64000 |
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Spicey |
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interface Serial1 ip address 5.0.2.2 255.255.255.0 encapsulation lapb |
Verify
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.
The output shown below is a result of entering these commands on the devices that are used in this sample configuration.
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show controllers - Shows that Prasit is the DCE and Spicey is the DTE. This command gives you information on whether the physical layer is working and what type of cable is connected.
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ping - Used to test the connection.
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show interfaces - Displays statistics for all interfaces configured on the router or access server.
prasit#show controllers serial 0 HD unit 0, idb = 0x1D3A2C, driver structure at 0x1DAFE8 buffer size 1524 HD unit 0, V.35 DCE cable, clockrate 64000 !--- Output suppressed here. spicey#show controllers serial 1 HD unit 1, idb = 0x153E94, driver structure at 0x15A1F8 buffer size 1524 HD unit 1, V.35 DTE cable !--- Output suppressed here.
The following command output is taken from Prasit.
prasit#ping 5.0.2.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 5.0.2.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/36/44 ms
prasit##show interfaces serial 0
Serial0 is up, line protocol is up
Hardware is HD64570
Internet address is 5.0.2.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation LAPB, loopback not set
LAPB DCE, state CONNECT, modulo 8, k 7, N1 12032, N2 20
T1 3000, T2 0, interface outage (partial T3) 0, T4 0, Protocol ip
VS 2, VR 3, tx NR 3, Remote VR 2, Retransmissions 0
Queues: U/S frames 0, I frames 0, unack. 0, reTx 0
IFRAMEs 10/11 RNRs 0/0 REJs 0/0 SABM/Es 1/0 FRMRs 0/0 DISCs 0/0
Last input 00:02:45, output 00:02:45, output hang never
Last clearing of "show interface" counters 00:10:14
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue :0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
12 packets input, 1080 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
14 packets output, 1028 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
The following command output is taken from Spicey.
spicey#ping 5.0.2.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 5.0.2.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/32/32 ms
spicey#show interface serial 0
Serial0 is up, line protocol is up
Hardware is HD64570
Internet address is 5.0.2.2/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation LAPB, loopback not set
LAPB DTE, state CONNECT, modulo 8, k 7, N1 12032, N2 20
T1 3000, T2 0, interface outage (partial T3) 0, T4 0, Protocol ip
VS 3, VR 2, tx NR 2, Remote VR 3, Retransmissions 0
Queues: U/S frames 0, I frames 0, unack. 0, reTx 0
IFRAMEs 11/10 RNRs 0/0 REJs 0/0 SABM/Es 0/1 FRMRs 0/0 DISCs 0/0
Last input 00:00:28, output 00:00:28, output hang never
Last clearing of "show interface" counters 00:06:33
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue :0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
14 packets input, 1028 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
12 packets output, 1080 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 output buffer failures, 0 output buffers swapped out
1 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
Troubleshoot
There is currently no specific troubleshooting information available for this configuration.
Related Information
| Updated: Jun 01, 2005 | Document ID: 7925 |