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QOS using CBWFQ - with Scenario's

Hello All,

I have a MPLS Circuit as Primary Link. Backup VPN over Internet as Secondary Link.

Internet Link Capacity is 10 Mbps & i need to use QOS using CBWFQ to Rate-Limit the Bandwidth as: 6 Mbps for Backup VPN over Internet & only 4 Mbps for Internet Usage.

My Scenario's are:

1. MPLS Link - UP

* Internet Utilization should be limited to only 4 Mbps

* Backup VPN Link should have dedicated 6 Mbps Bandwidth allocated.

2. MPLS Link - DOWN

* Backup VPN Link gets Activated

* Backup VPN Link Capacity should be 6 Mbps & it should be expandable even upto 8 Mbps + more of Utilization (if Incoming & Outgoing is High) inorder to avoid the Burst of Traffic

* Whereas rest of the availaible Bandwidth is for Internet in this Scenario

* Consider High Priority for traffic over Backup VPN & Low Priority for Internet Traffic

* Also, If Backup VPN Link Utilization is less than 6 Mbps means Internet Usage can expand to 4 Mbps & not more than 4 Mbps of Bandwidth

Can anyone help me with the Sample Configuration for this Setup & Scenario's

Thanks in Advance ! ! ! !

Thanks & Regards,

Guru Prasad R

Cisco Employee

Re: QOS using CBWFQ - with Scenario's


given your requirements the closest implementation I can think of looks like this:

interface Ethernet0

description Internet link

max-res 80

class-map match-any VPNBackup

match ip adress 100

!ACL 100 should describe your backup VPN link traffic

policy-map ToInet

class VPNBackup

bandwidth 8000

class class-default



shape average 4000000

This does not exactly do, what you want, but is as close as it can be. What it does:

1) limits internet access to 4 Mbps at any time (shape command) as requested

2) guarantees 8 Mbps to backup VPN traffic, IF there is so much traffic.

In fact, Backup VPN traffic can use the whole interface bandwidth if there is no other traffic - this is how CBWFQ works.

Be aware, that unfortunately there is no possibility for QoS "if, then" configuration.

Also be aware that this only controls the uplink direction. There is no guarantee for the download direction unless the ISP is invoked and applies a similar QoS policy on his equipment for your interface.

Hope this helps!

Regards, Martin

Re: QOS using CBWFQ - with Scenario's

HI Martin,

Thanks for your Sample's. What is "max-res 80" - ? ? ? ?

I would like to add some more commentes in my requirement.

I am going to configure QOS using CBWFQ for this Requirement in my Internal Interface of the Internet Router. Service Provider is just providing me a 10 Mbps Link only & no QOS definitions on ISP Side.

Internet Router:


Interface Fast Eth 0/0

----Connected to Service provider MUX

Interface Fast Eth 0/1

----Connected to my DMZ Switch

Infact, i need to apply this QOS using CBWFQ in Interface Fast Eth 0/1.

Can you provide samples on:


1. Backup is 6 Mbps only & it can "expand/grow" upto 8 Mbps + more if INCOMING & OUTGOING is HIGH

2. Rest of the availaible Bandwidth is only for Internet

3. ie., High priority for Backup VPN & LOW Priority for Internet

4. No Backup VPN Usage(ie., MPLS=UP) / Backup Usage is less than 6 Mbps means Internet Usage should grow only upto 4 Mbps at any point of time.

NOTE: Can you please judge whether my requirement is like "if, then" - as you say it is not possible with QOS

Thanks for your previous Post with samples, helped me a lot. Expecting your earlier Advices with samples to proceed further.

Best Regards,

Guru Prasad R