[c-nsp] Cisco 3400 port shaping message limitation

[Tassos Chatzithomaoglou]

This has to do with the granularity of the ME-3400 hardware for the shaping action.

There is a formula for port shaping ( 1 - 16/N ) * rate, where N is from 17 to 64K, that can give you all the possible 
values (rate is the interface speed). As you can see from the formula, you have awful granularity at the low end and 
very good granularity at the high end. The opposite is happening with class-based shaping.

Btw, ME-3400E is much better on this one.


--
Tassos

Pavel Skovajsa wrote on 07/10/2009 19:20:
> Hello all,
> 
> I was in the middle of the configuration of ME-3400-24TS-A
> (12.2(50)SE1) for port-shaping and run into interesting message:
> 
> censw(config-if)#!
> censw(config-if)#!
> censw(config-if)#interface FastEthernet0/12
> censw(config-if)#service-policy output UNI-out-internet-1024kbps
> censw(config-if)#service-policy input UNI-in-internet-1024kbps
> censw(config-if)#!
> censw(config-if)#!
> censw(config-if)#interface FastEthernet0/22
> censw(config-if)#service-policy output UNI-out-internet-1024kbps
> censw(config-if)#service-policy input UNI-in-internet-1024kbps
> censw(config-if)#!
> censw(config-if)#!
> censw(config-if)#interface FastEthernet0/5
> censw(config-if)#service-policy output UNI-out-internet-1024kbps
> QoS: Configuration failed.  The configured rate 1024000 bps is not
> achievable in hw within 1% of configuration.
>         Closest value(s) are: 1111111 bps, 1000000 bps
> censw(config-if)#service-policy input UNI-in-internet-1024kbps
> censw(config-if)#
> censw(config-if)#service-policy output UNI-out-internet-1024kbps
> QoS: Configuration failed.  The configured rate 1024000 bps is not
> achievable in hw within 1% of configuration.
>         Closest value(s) are: 1111111 bps, 1000000 bps
> censw(config-if)#service-policy output UNI-out-internet-1024kbps
> QoS: Configuration failed.  The configured rate 1024000 bps is not
> achievable in hw within 1% of configuration.
>         Closest value(s) are: 1111111 bps, 1000000 bps
> 
> 
> The configuration of the policy-map is straightforward:
> policy-map UNI-out-internet-1024kbps
>  class class-default
>     shape average 1024000
>     queue-limit 272
> 
> The setting of the queue-limit is configured according to the
> recommendation over here:
> http://www.cisco.com/en/US/docs/switches/metro/me3400/software/release/12.2_52_se/configuration/guide/swqos.html#wp1497063
> 
> After little experimenting I figured out that when I change the
> policy-map to this:
> policy-map UNI-out-internet-1024kbps
>  class class-default
>     shape average 1000000
>     queue-limit 272
> 
> It starts to work fine. The question still remains, what does this
> error message actually mean, and why it got triggered when I applied
> the policy to the 3rd interface in a row....
> 
> Can somebody shed some light into this?
> 
> Regards,
> Pavel Skovajsa
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