QOS based on IP subnets

Unanswered Question
Apr 25th, 2008

Hey guys,

I was wondering if it would be possible to do prioritization based on IP subnets? I have one subnet for internet access but runs through the same switches as the most important traffic. How could I give priority to the more important subnet? Thanks in advance!

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Overall Rating: 5 (2 ratings)
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PAUL TRIVINO Fri, 04/25/2008 - 15:40

Surely. You simply set up your subnet to be matched:

ip access-list extended priority-subnet

permit ip any 192.168.1.0 255.255.255.0 <= if by destination

permit ip 192.168.1.0 255.255.255.0 any <= if by source

Then do a class for that ACL:

class-map match-all CLASS-PRIO-NET

match access-group name priority-subnet

Then put it in a policy:

policy-map QOS-POLICY

class CLASS-PRIO-NET

priority percent 35

Hope that's not too much info or oversimplified.

Paul

justinfvoeller Mon, 04/28/2008 - 07:13

Thank you for that!!!

If I wanted to give one subnet 95% of the bandwidth, what would happen to the other subnets?

Also, is there a way that I can push this to switches to do qos at their level?

PAUL TRIVINO Mon, 04/28/2008 - 07:46

Not a simple question, but basically the bandwidth limits you set are only in cases where there is not enough bandwidth. If you give a class 95%, and 95% is available, it gets it. The exception is LLQ - "priority" keyword - where anything that exceeds the LLQ bandwidth is dropped. I.e., you can burst UP into LLQ bandwidth if it's available, but you can't burst down (exceed LLQ limits).

*Generally* (and it's a HUGE generalization), you use switches to mark traffic at the edge and use routers to enforce the limits, at least at remote sites. You can do limits on switches but it is not easy (compared to MQC).

Check the QoS SRND Guide, it is an excellent resource. http://www.cisco.com/en/US/netsol/ns656/networking_solutions_program_home.html

Paul

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