QOS on ME3400

pbenin · ‎03-14-2007

Hi,

I?d like to highlight a problem we have configuring "Priority with Police" on a CiscoME3400 switch.

Following the indications in the configuration guide, once the service policy is applied to the interface on the switch the following error occurs:

class-map match-all GOLD

match ip dscp ef

class-map match-all BE

match ip dscp default

class-map match-all BRONZE

match ip dscp af21

class-map match-all SILVER

match ip dscp af11

!

policy-map LLQ

class GOLD

police cir 512000

priority

class SILVER

shape average 256000

class BRONZE

bandwidth 1000

policy-map SHAPING-OUT

class class-default

shape average 2000000

service-policy LLQ

ME3400_amps(config-pmap-c)#INT FA0/3

ME3400_amps(config-if)#Speed 10

ME3400_amps(config-if)#Duplex Full

ME3400_amps(config-if)#SERvice-policy OUtput SHAPING-OUT

QoS: Configuration failed. The configured rate is not achievable in hw within 1

% of configuration.

Closest value(s) are: 526315 bps, 500000 bps

The error does not occur while modifying the bandwidth in the policy map (for example to 256Kbps).

Similar errors have occurred during configurations which involve Class Based Shaping (QoS Parent-Child).

Are there specific indications or calculations for defining bandwidth parameters?

Look forward to receiving any suggestions on resolving these problems.

Thanks.

doddsb · ‎03-19-2007

Here is the answer from TAC when I asked the same question in Jan 07.

The error message can be explained by the fact that Hardware interface shaping granularity is (1-16/N) times the line rate where N=17...64000.

For example for Gigabit the shape rates would become: 58.8M =(1-16/17)x1G, 111.1M, 157.9M, 200.0M, 238.1M, 272.7M, 304.3M, 333.3M, ..., 999.6M, 999.7M, 999.8M =(1-16/64000)x1G.

For 100M interface this mean that minimum is about 6M.

In other words, the low end granularity is very coarse but the high end granularity is very fine. This is actually due to the hardware architecture, meaning also that this is something that cannot be changed.

The error message suggests you the closest value permitted:

"Closest value(s) are: 526315 bps, 500000 bps"

With these values the configuration will be accepted.