Cisco CCNA Exam Tutorial: Troubleshooting Directly Connected Serial Interfaces - 0 views

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  #1 Stender Albrechtsen on 23 Oct 13

   

  CCNA examination success depends largely on noticing the facts, and this is especially true of adjustments involving directly connected serial interfaces. To study additional information, we know people glance at: find out more. And obviously, it's insufficient to observe these details - you have got to understand what to do about them!
  
  A Cisco router is just a DTE by default, but right connecting two DTEs using a DCE/DTE cable isn't enough. In the following example, R1 and R3 are directly linked at their Serial1 interfaces. Stockport Pest Controller Investigation is a compelling library for new information about the reason for it. The line goes up shortly after being exposed, however the line method goes down after about 30 seconds.
  
  R3( config-if )#int s1
  
  R3( config-if )#ip address 172.12.13.3 255.255.255.0
  
  R3( config-if )#no shutdown
  
  2d18h: %LINK-3-UPDOWN: Interface Serial1, changed state to up
  
  2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, improved state to up
  
  R3( config-if )#
  
  2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down
  
  The problem is that one of the hubs wants to become the DCE in order for the line method to come up and stay up. You could just review and take a look at the DTE/DCE cable to view which switch had the DCE end of the cable connected, if this were your CCNA / CCNP home lab. In this example, though, we don't have physical access to the hubs. How do we tell which switch has the DCE end-of the cable connected?
  
  R3#show controller sequential 1
  
  HD uni-t 1, idb = 0x1C44E8, driver structure at 0x1CBAC8
  
  buffer size 1524 HD device 1, V.35 DCE cable
  
  The show operator control gives us this information. (There is a lot more production that this with this command, but it is unimportant for our purposes.) The router with the DCE end of the cable needs to provide a time rate to the DTE, and we'll do just that with the interface-level clockrate command.
  
  R3#conf t
  
  Enter configuration commands, one per line. Be taught further on this partner wiki by browsing to the internet. End with CNTL/Z.
  
  R3( config )#int serial1
  
  R3( config-if )#clockrate 56000
  
  2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, improved state to up
  
  In just a matter of seconds, the line method remains up and goes up.
  
  When troubleshooting an association, often run show screen first. The connection is physically good but realistically down, If you see the mixture found below. That's broadly speaking the result of a needed keepalive maybe not being present. With Frame Relay, it's probably an issue, but with directly related serial interfaces the issue is almost certainly the DCE end of the connection not delivering clockrate.
  
  R3#show interface serial 1
  
  Serial1 is up, line protocol is down
  
  Troubleshooting is a big part of the job, and it's a part of the Cisco CCNA and CCNP programs as well. Know your present and debug commands and you are on the road to passing the CCNA!.

   

  <div class="cArrow"> </div><div class="cContentInner">CCNA examination success depends largely on noticing the facts, and this is especially true of adjustments involving directly connected serial interfaces. To study additional information, we know people glance at: <a rel="nofollow" href="http://passfastnorthwest.co.uk/">find out more</a>. And obviously, it's insufficient to observe these details - you have got to understand what to do about them! <br /> <br /> A Cisco router is just a DTE by default, but right connecting two DTEs using a DCE/DTE cable isn't enough. In the following example, R1 and R3 are directly linked at their Serial1 interfaces. <a rel="nofollow" href="http://www.stockportpestcontroller.co.uk/">Stockport Pest Controller Investigation</a> is a compelling library for new information about the reason for it. The line goes up shortly after being exposed, however the line method goes down after about 30 seconds. <br /> <br /> R3( config-if )#int s1 <br /> <br /> R3( config-if )#ip address 172.12.13.3 255.255.255.0 <br /> <br /> R3( config-if )#no shutdown <br /> <br /> 2d18h: %LINK-3-UPDOWN: Interface Serial1, changed state to up <br /> <br /> 2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, improved state to up <br /> <br /> R3( config-if )# <br /> <br /> 2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down <br /> <br /> The problem is that one of the hubs wants to become the DCE in order for the line method to come up and stay up. You could just review and take a look at the DTE/DCE cable to view which switch had the DCE end of the cable connected, if this were your CCNA / CCNP home lab. In this example, though, we don't have physical access to the hubs. How do we tell which switch has the DCE end-of the cable connected? <br /> <br /> R3#show controller sequential 1 <br /> <br /> HD uni-t 1, idb = 0x1C44E8, driver structure at 0x1CBAC8 <br /> <br /> buffer size 1524 HD device 1, V.35 DCE cable <br /> <br /> The show operator control gives us this information. (There is a lot more production that this with this command, but it is unimportant for our purposes.) The router with the DCE end of the cable needs to provide a time rate to the DTE, and we'll do just that with the interface-level clockrate command. <br /> <br /> R3#conf t <br /> <br /> Enter configuration commands, one per line. Be taught further on this partner wiki by browsing to <a rel="nofollow" href="http://www.stockportpestcontroller.co.uk/">the internet</a>. End with CNTL/Z. <br /> <br /> R3( config )#int serial1 <br /> <br /> R3( config-if )#clockrate 56000 <br /> <br /> 2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, improved state to up <br /> <br /> In just a matter of seconds, the line method remains up and goes up. <br /> <br /> When troubleshooting an association, often run show screen first. The connection is physically good but realistically down, If you see the mixture found below. That's broadly speaking the result of a needed keepalive maybe not being present. With Frame Relay, it's probably an issue, but with directly related serial interfaces the issue is almost certainly the DCE end of the connection not delivering clockrate. <br /> <br /> R3#show interface serial 1 <br /> <br /> Serial1 is up, line protocol is down <br /> <br /> Troubleshooting is a big part of the job, and it's a part of the Cisco CCNA and CCNP programs as well. Know your present and debug commands and you are on the road to passing the CCNA!.</div>

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