HQoS order of operations. WRED in parent and child policies

[MaximBudyonny]

Hello,

when branch is connected to HQ via  the 512K link QoS is the must.

So, QoS is configured:

policy-map WAN-CHILD

class VOIP-STREAM

   priority percent 70

class VOIP-SIGNALING

   bandwidth remaining percent 5

class PRIORITY-1

   bandwidth remaining percent 10

class PRIORITY-2

   bandwidth remaining percent 15

class class-default

   fair-queue

     random-detect

policy-map 512K

class class-default

   shape average 500000 5000

     random-detect dscp-based

service-policy WAN-CHILD

interface FastEthernet0

bandwidth 512

ip address 172.22.0.18 255.255.255.252

tx-ring-limit 2

tx-queue-limit 2

service-policy output 512K

When link is congested what would be the order of operations? (I have read http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a0080160fc1.shtml )

1. Shaping to the rate configured in the policy 512K
2. Droping packets with WRED configured in the policy 512K
3. Queuing with the CBWFQ child policy WAN-CHILD

Is it mutual exclusive to configure WRED on the parent policy and child policy?

[John Blakley]

I don't think you're going to need to configure a class-default under your WAN-CHILD policy since it will be caught with your 512K policy. Anything else that matches under your WAN-CHILD policy would still be caught, and then your fall back would obviously be the 512K class-default class.

John

[Joseph W. Doherty]

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Posting

Since yours is a hierarchal policy, WRED might be "legal" in the parent policy, but shaper caused congestion should be pushed (mostly) down to the child policy.  I.e. WRED might not see enough congestion at the parent level to activate, but if it does, it will be applied to all packets in that class.

Cisco recommends against such a high bandwidth proportion allocated for LLQ, as you've done in the child policy.

Since you're using bandwidth remaining for your non-LLQ classes, together they can sum up to 100.  From the way you've allocated them, it appears you were trying to allocate the 30% not used by the LLQ class.

If you using a version of IOS pre-HQF, FQ in class-default can distort your non-LLQ bandwidth allocations.

Unless you really understand WRED, recommend you don't use it, especially with its default settings, or together with FQ.

[MaximBudyonny]

Thank you for reply.

So, shaping will be pushed down to the child policy, while WRED would be implemented on the parent level  policy, i.e.

policy-map WAN-CHILD

class VOIP-STREAM

    priority percent 70

class VOIP-SIGNALING

    bandwidth remaining percent 5

class PRIORITY-1

    bandwidth remaining percent 10

class PRIORITY-2

    bandwidth remaining percent 15

    random-detect

!------------ RED was added here because this class matches potentially bursting traffic

!------------ no WRED, because all traffic belongs to one class

class class-default

    fair-queue

!------------- my IOS supports HQoS . In any case, I think  queue per  flow that would be created by the fair-queue

mechanism is more preferable mechanism of bandwidth allocation instead of simple FIFO

!------------- The new one child policy to implement shaping

policy-map WAN-CHILD-2

class class-default

    shape average 500000 5000

service-policy WAN-CHILD

!------------- The new one parent policy

policy-map PARENT

class class-default

     random-detect dscp-based

  service-policy WAN-CHILD2

interface FastEthernet0

bandwidth 512

ip address 172.22.0.18 255.255.255.252

tx-ring-limit 2

tx-queue-limit 2

service-policy output PARENT