Routing

Hi Experts

What is the difference between shaping and policing? According to Juniper documentation shaping is defined in terms of Committed information rate (CIR) and Peak Information rate (PIR) but I believe when we define policer then we define CIR and PIR (in two rate thee colour policer). So I did not get what is actually shaping?

Thanks

Hi,

I usually use below representative to differentiate policing and shaping. If you see the difference, policing is strict in cutting off the traffic which is above CIR and Shaping uses buffers to allow more traffic without exceeding CIR. However with shaping there are latency issues as it buffers certain amount of traffic.

Regards

Surya Prakash

Also, policing (e.g. firewall policers) takes place before shaping.

Thanks Surya

Also, a way to think about it is this.... difference between policing and shaping.... which word sounds worse?  You guessed it... policing sounds worse than shaping.  Because it is.  Policer drops any traffic over a certain allowed amount, shaping doesn't drop it right away, as shaping will try it's best to send it, but in a delayed manner.  As someone else mentioned, shaping will buffer the overage, and try to send it at some later time interval... but the point is, it tries.  Policing doesn't try.... policing just drops it.

Also, I've learned that if your traffic is getting policed at a certain rate, and you need to fit more traffic through a policing mechanism upstream, then you will need to shape your traffic at your egress before ingressing the policing node.

I also beleive there isn't a replacement to more bandwidth... and if you need more sustained bandwidth, then you will probably need to purchase it.  QoS solves some things, but QoS won't create more bandwidth over the long term.  Shaping will solve occassional burst above a policed rate, but, shaping will not solve long lasting sustained traffic above the policed rate.  You can overwhelm a shaper thus causing the shaper to run out of its buffer space and thus drop packets.... but it won't be because the shaper didn't try 🙂  ...it will be because you are overflowing the shaper.