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  • Content created by Rene Molenaar (CCIE #41726)


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Notable Replies

  1. Hi Rene, Great explanation of shaping, its quite hard to find this sort of detail in an easy to understand format. One question regarding rate-limiting vs shaping. Although rate-limiting does not buffer/queue packets, is it capable of slowing the rate to the contracted bandwidth? For example, if I have a 1GB fibre to a provider switch but only have say 50mb contracted, can I use rate-limiting to prevent the router transmitting at a 1GB clock rate or is shaping the only method of achieving this?

  2. Hi Brendan, glad to hear you like it. Do you refer to rate-limiting on a router or switch?

    On routers you have the "rate-limit" command but it's the "legacy QoS" method of configuring policing, it can be applied inbound or outbound.

    On the Catalyst Switches (eg 3560) you can use the "srr-queue bandwidth limit " to limit outgoing traffic but I believe this is a shaper.

  3. This is one awesome posts about QoS policing and shaping .U don't find like this many out there.And I should thank U for this.
    BTW, I have few questions reg this,

    1.In this example that you have demonstrated on what basis the Tc (Time Interval) value was chosen. i,e 62.5 in this case ? (62.5 + 62.5 =125).Is there any logic behind it?

    Expecting the earliest reply..

    Thanks in Advance,

  4. Hi Sai,

    I'm glad to hear that you like it. Cisco routers have a default Tc of 125 ms so that there are 8 intervals, not sure why they decided to go with this value. You can change it if you like it to a lower value (10 ms on most Cisco routers) which is a good idea for VoIP traffic...


  5. Hi Rene.Thanks for your Perfect article. Lets say traffic is passing from R1 to R2 and I configured shaping (avarage shaping 1mbps).

    show policy-map interface 
      Service-policy output: TEST
        Class-map: class-default (match-any)  
          13774 packets, 1089848 bytes
          30 second offered rate 0000 bps, drop rate 0000 bps
          Match: any 
          queue limit 64 packets
          (queue depth/total drops/no-buffer drops) 0/0/0
          (pkts output/bytes output) 358/43444
          shape (average) cir 1000000, bc 4000, be 4000
          target shape rate 1000000

    This is a CSR1000V and default Tc value is 4 ms

    it means we have 250 section. From each section during the 4 ms , 4000 token(bit) can pass. On condition that more bits pass through the R1 druring the 4 ms , (not 4000 bit lets say 6000 bit) they wil drop. Can you explain me please, when the fragmentation will occur in this case?

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