3750 hierarchical MQC

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Aug 5th, 2009
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I have a requirement on the 3750 to shape traffic for Vlan 15 and 16 to 4 Mb while giving vlan 16 priority over vlan 15. Vlan 16 can suck all the bandwidth and make vlan 15 starve.

I implemented MQC with nested policied but didnt work. First I used the following:

class-map match-any VLAN15OR16

match vlan 15

match vlan 16

class-map match-any VLAN16

match vlan 16

policy-map CHILD

class VLAN16

bandwidth 4000

policy-map PARENT

class VLAN15OR16

shape average 4000000

service-policy child

when applying the service policy on the ES port it gives me the following error:

QoS: Invalid class policy CHILD

QoS: Invalid child policy CHILD

I replaced the "bandwidth 4000" with "priority" command then I got the following error when applying the policy:

"Priority is not allowed in logical class"

QoS with 3750 seems to work in a diff manner. Any suggestions on how to implement the requirement above!



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paolo bevilacqua Sat, 08/08/2009 - 11:12
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Priority doesn't make much sense on a switch.

Fast interfaces are never congested, so no priority is ever needed.

ali.mousawi Sun, 08/09/2009 - 22:07
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ok no priority but how can i acheive the requirement? Using IPP will put traffic in the right Qs and it works but the client do not want to do any additional config on their equipment and am left by matching on VLANs.

Pavel Bykov Thu, 01/28/2010 - 08:20
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Paolo, how come you think that?

Quite on the contrary, switch interfaces are always "congested", if by congestion we are talking about the interface is in "ON" state (sending a packet) and there are some packets that are in queue waiting for departure.

The more packets you have in queue, the more they have to wait. All queues are serviced using some round robins, and we don't want for a voice packet to wait it's turn to be sent or share the bandwidth for other flows for that matter. Just think of an almost 100 MB buffer on 6708 linecard. That's quite some wait time - about 80 miliseconds even on 10G interface.

So pripority queue is extremely important, because we don't want some packets to gain 80 ms delay on one node, when there are still 10 nodes to go in the way.

anders.nordseth Thu, 01/21/2010 - 03:58
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I believe policy-maps are case sensitive, and you have a mismatch using both 'child' and 'CHILD'.


Pavel Bykov Thu, 01/28/2010 - 08:25
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From QoS perspective, 3750ME is a special case.

You can imagine it better if you imagine 3750-24TS with a SIP-400-type router attached via 2Gbps internal etherchannel to it.

So you need to do QoS on 3750 part and on ES part separately.

Because ES ports are connected via internal VLAN they can only match DSCP in the packet, or copy COS to EXP. No special mathes are allowed on ES ports, since packet never carries information on what VLAN it originated from, what port, etc.

If you'll do QoS for ES ports just like for the router, matching DSCP/EXP, IP information, etc, and do standard "mls qos" for the standard ports, it will all work.

Just remember, ES facility is very limited performance-wise since it's a software platform. So the more functions you type, the slower it'll become, just like 7201 router.


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