Lab Objective:
The objective of this lab exercise is to configure back-to-back Serial interfaces between two Cisco routers. By default, router Serial interfaces receive their clocking information from an external device such as a CSU/DSU.
Lab Purpose:
Back-to-back Serial interface configuration is a fundamental skill. Because routers typically receive clocking from an external device such as a CSU/DSU, it is imperative to understand how to bring up a back-to-back Serial connection between two routers to set up your home lab, for example. As a Cisco engineer, as well as in the Cisco CCNA exam, you will be expected to know how to configure back-to-back Serial connections.
Certification Level:
This lab is suitable for both CCENT and CCNA certification exam preparation.
Lab Difficulty:
This lab has a difficulty rating of 3/10.
Readiness Assessment:
When you are ready for your certification exam, you should complete this lab in no more than 10 minutes.
Lab Topology:
Please use the following topology to complete this lab exercise:
Task 1:
Configure hostnames on R1 and R2 as illustrated in the topology.
Task 2:
Enable Serial interfaces on R1 and R2. The Serial0/0 interface on R2 is identified as the DCE in the topology. Use the appropriate show command to verify that this interface is indeed the DCE.
Task 3:
Configure the DCE interface on R2 to provide clocking to R1. The clock speed should be 256 Kbps. Remember that 1 Kbps = 1000 bps. Verify that R1 receives clocking information from R2.
Task 4:
Configure IP addressing on R1 and R2 Serial0/0 interfaces as illustrated in the topology.
Task 5:
Verify your interface status and ping between R1 and R2 to validate connectivity.
Configuration and Verification
Task 1:
For reference information on configuring hostnames, please refer to earlier labs.
Task 2:
R1(config)#interface serial0/0 R1(config-if)#no shut *Mar 1 00:36:47.282: %LINK-3-UPDOWN: Interface Serial0/0, changed state to down R1(config-if)#end R1# R2(config)#interface serial0/0 R2(config-if)#no shut *Mar 1 00:36:47.282: %LINK-3-UPDOWN: Interface Serial0/0, changed state to down R2(config-if)#end R2#show controllers serial 0/0 Interface Serial0/0 Hardware is PowerQUICC MPC860 DCE V.35, no clock
NOTE: The show controllers command will tell you whether the interface is the DCE side (which provides the clocking) or the DTE side (which receives the clocking) on a particular router interface. Note that GNS3 doesn’t use actual cables so there is no need to configure clocking.
Task 3:
R2#conf t Enter configuration commands, one per line. End with CTRL/Z. R2(config)#interface serial0/0 R2(config-if)#clock rate 256000 R2(config-if)#end R2#show controllers serial0/0 Interface Serial0/0 Hardware is PowerQUICC MPC860 DCE V.35, clock rate 256000 R1#show controllers serial0/2 Interface Serial0/0 Hardware is PowerQUICC MPC860 DTE V.35 TX and RX clocks detected.
Task 4:
For reference information on configuring IP addressing, please refer to earlier labs.
Task 5:
R1#show ip interface brief Interface IP-Address OK? Method Status Protocol Serial0/0 172.30.100.1 YES manual up up R1#ping 172.30.100.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.30.100.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms R2#show ip interface brief Interface IP-Address OK? Method Status Protocol Serial0/0 172.30.100.2 YES manual up up R2#ping 172.30.100.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.30.100.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms