Backup traffic is killing our WAN link and want to know if this policy makes sense

[agreenwald]

Hi,

  We are trying to make sure that our backup servers do not kill our WAN bandwidth.  We have a Cisco 3640 router with 100 Megabit link that is limited to  30 Megabits/sec.  Here is a policy we came up with.  Will this make sure the classes of traffic are guaranteed bandwidth during congestion and that the backup traffic only gets 1% when we hit close to 30Meg/sec.  Will my class-default take the 9% of traffic,

Thank you.

policy-map MYQOS

class voice

  priority percent 80

class apps

  bandwidth remaining percent 60

  random-detect dscp-based

  set ip dscp af31

class signalling

  bandwidth remaining percent 30

  random-detect dscp-based

class backuptraffic

  bandwidth percent 1

class class-default

  fair-queue

  random-detect dscp-based

policy-map SHAPER

class class-default

  shape average 30000000

  service-policy MYQOS

[Giuseppe Larosa]

Hello Agreenwald,

your QoS configuration looks like correct with a parent shaper creating a 30 Mbps pipe and the nested policy implementing queueing.

CBWFQ is elastic so each class can use more then stated percentages when congestion does not occur that in nested policies means if aggregate traffic rate is less then 30 Mbps. So the percentages are the guaranteed minimum values when the pipe is full and shaping is occurring on the parent policy.

However, this handles the outbound direction only.

A similar setup is needed on the router on the other end of the WAN link to handle the other direction

Hope  to help

Giuseppe

[Joseph W. Doherty]

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Posting

What you have is basically correct, although application of the policy might balk over mixing remaining percent and percent in different classes.

Some suggestions include:

Your LLQ percentage is very high.  Generally recommendation is to not exceed about 1/3 of bandwidth.

On pre-HQF CBWFQ, activation of FQ in class-default can "steal" bandwidth from your other classes.

I generally recommend not using WRED, unless you're really understand how to use it.

You might just want to try:

policy-map MYQOS

class voice

  priority percent 30

class backuptraffic

  bandwidth remaining percent 1

class class-default

  fair-queue

policy-map SHAPER

class class-default

  shape average 30000000

  service-policy MYQOS

Also to support VoIP, you may want to reduce tx-ring-limit on the egress interface, and with an older IOS, adjust the shaper's Bc so Tc is 10ms or less.

If you still really need to mark your apps with AF31, that could be done on an ingress policy (the above, with pre-HQF CBWFQ, preserves FQ for your app traffic too).