02-12-2008 12:07 AM - edited 03-05-2019 09:05 PM
Hi,
Does QoS cause Router's CPU overhead?, and if it does, is it acceptable? Especially the router configured with little number of policies.
Thanks
Solved! Go to Solution.
02-12-2008 05:17 AM
"Does QoS cause Router's CPU overhead?"
Usually, some. Especially on pure routers. (L3 switches often support their QoS features within hardware.)
"if it does, is it acceptable?"
Depends much on how busy the router is before you apply the policy and what the QoS policy is doing.
"Especially the router configured with little number of policies."
Not just an issue of number of policies, but it's often more a question of what's being done within the policy or policies.
The question of the impact of QoS configuration to the router's performance is somewhat similar to performance impact questions when adding any other services feature, e.g. ACLs.
My experience has been I've rarely seen more than an additional 5% increase to the CPU load and the benefits make it worthwhile.
02-12-2008 11:33 AM
Both Narayan and David do well to caution about usage of NBAR, which, I think, emphasizes my point about what the QoS policy is actually doing. Some QoS features are much more resource intensive than others.
David's post, indirectly, touches on an issue which I didn't mention, it's possible multiple service interactions can especially degrade performance if the fast switching path reverts to software switching.
If both Narayan and David are implying, proceed with caution, they're certainly correct.
02-12-2008 05:17 AM
"Does QoS cause Router's CPU overhead?"
Usually, some. Especially on pure routers. (L3 switches often support their QoS features within hardware.)
"if it does, is it acceptable?"
Depends much on how busy the router is before you apply the policy and what the QoS policy is doing.
"Especially the router configured with little number of policies."
Not just an issue of number of policies, but it's often more a question of what's being done within the policy or policies.
The question of the impact of QoS configuration to the router's performance is somewhat similar to performance impact questions when adding any other services feature, e.g. ACLs.
My experience has been I've rarely seen more than an additional 5% increase to the CPU load and the benefits make it worthwhile.
02-12-2008 06:11 AM
Just to add on Joseph's post, if you are using NBAR for classifying traffic and have many traffic classes, you might see a considerable increase in the CPU
Narayan
02-12-2008 06:44 AM
This is my experience with Cisco 2621 router.
This router is running IOS 12.3(24) with
firewall feature set. It also has NAT and
CBAC. The router is connected to a cable
modem 5Mbps down and 2Mbps up. CPU is running
at 9% CPU.
When I enable QoS and NBAR on the router to
limit P2P and FTP apps, the CPU goes from
9% to 98%. Not only that, the router locks
up every 3 hours and I can no longer telnet
or ssh into the router, and that I have to
power OFF/ON the router. This happens every
3 hours.
When I disable QoS and NBAR, the issue goes
away.
You need to be careful when using these in
your production environment.
CCIE Security
02-12-2008 11:33 AM
Both Narayan and David do well to caution about usage of NBAR, which, I think, emphasizes my point about what the QoS policy is actually doing. Some QoS features are much more resource intensive than others.
David's post, indirectly, touches on an issue which I didn't mention, it's possible multiple service interactions can especially degrade performance if the fast switching path reverts to software switching.
If both Narayan and David are implying, proceed with caution, they're certainly correct.
02-12-2008 11:45 PM
Hi,
Thank you very much for your helpful opinions, so i'll proceed with caution and get back with the result may be it will help someone else.
Thanks
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