Clockrate Command

Daniel333Daniel333 Posts: 2,077Member ■■■■■■□□□□
Alright, sorry to be bothering you guys so much today. But hey, what I ask today, might help someone tomorrow. I am studying for the CCNA-Intro exam, so the books I have are kind limited. They alll give examples of either setting the clockrate on the DCE at either 64000 or 128000, which seems off to me. Should be we setting that much higher to support the 10Mpbs the router's Serial ports should be supporting?

Where have I gone wrong on this assumption?
-Daniel

Comments

  • PashPash Posts: 1,601Member ■■■■■□□□□□
    Well yes, if this is a lab or simulation you are trying to test on you could set your speed as much as allowed by your serial port (infact im not sure of the speeds, you could probably find out from the cisco website dependent on several factors). However, most of the examples provided by cisco press and other study vendors will mention 64k and 128k many times because the DCE equipment in real world scenarios usually sits in an ISP centre, because obviously they decide the physical speed of your p2p connection, if the customer were allowed to set the clockrate then....well you get the idea.
    DevOps Engineer and Security Champion. https://blog.pash.by - I am trying to find my writing style, so please bear with me.
  • mikej412mikej412 Posts: 10,090Member
    Most of the time 56k or 64k is chosen because those speeds will work with most Synchronous or Asyncronous Serial ports. 128k may be chosen because that's the max for the async serial port.

    Clock rate options for Synchronous Serial port
    R2511-2(config-if)#clock rate ?
            Speed (bits per second)
      1200
      2400
      4800
      9600
      19200
      38400
      56000
      64000
      72000
      125000
      148000
      250000
      500000
      800000
      1000000
      1300000
      2000000
      4000000
    
      <300-4000000>    Choose clockrate from list above
    

    And from an Asynchronous Serial port
    R3620-4(config-if)#clock rate ?
            Speed (bits per second)
      300
      1200
      2400
      4800
      9600
      14400
      19200
      28800
      32000
      38400
      56000
      57600
      64000
      72000
      115200
      128000
    
      <300-4000000>    Choose clockrate from list above
    

    HSSI interfaces may run up to 52Mbps -- but I don't have any in my home lab.
    :mike: Cisco Certifications -- Collect the Entire Set!
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