31 Days Before Your CCNA Exam

Day 16 171The IP address should be correct, and the interface status should be “up” and “up”. Table 16-2summarizes the two status codes and their meanings.Table 16-2Interface Status CodesName Location General MeaningLine status First status code Refers to the Layer 1 status—for example, is the cable installed, is itthe right/wrong cable, is the device on the other end powered on?Protocol Second status code Refers generally to the Layer 2 status. It is always down if the linestatusstatus is down. If the line status is up, a protocol status of down usuallyis caused by mismatched data link layer configuration.Four combinations of settings exist for the status codes when troubleshooting a network. Table 16-3 lists the four combinations, along with an explanation of the typical reasons why an interfacewould be in that state.Table 16-3Combinations of Interface Status CodesLine and Protocol StatusAdministratively down, downdown, downup, downup, upTypical ReasonsThe interface has a shutdown command configured on it.The interface has a no shutdown command configured, but the physicallayer has a problem. For example, no cable has been attached to the interface,or with Ethernet, the switch interface on the other end of the cable isshut down, or the switch is powered off.Almost always refers to data link layer problems, most often configurationproblems. For example, serial links have this combination when onerouter was configured to use PPP, and the other defaults to use HDLC.All is well, interface is functioning.If necessary, use the more verbose show interfaces command if you need to track down a problemwith an interface. Example 16-3 shows the output for FastEthernet 0/0.Example 16-3The show interfaces CommandR1#show interfaces fastethernet 0/0FastEthernet0/0 is up, line protocol is up (connected)Hardware is Lance, address is 0007.eca7.1511 (bia 00e0.f7e4.e47e)Description: R1 LANInternet address is 192.168.1.1/24MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, rely 255/255, load 1/255Encapsulation ARPA, loopback not setARP type: ARPA, ARP Timeout 04:00:00,Last input 00:00:08, output 00:00:05, output hang neverLast clearing of “show interface” counters neverQueueing strategy: fifo