SG-500 high cpu utilization

[rbolforski]

Hello,

I have one sg-500-52 acting as L3 switch (router mode) and I'm noticing high cpu utilization - 'show cpu utilization' almost always prints that switch cpu is loaded in 100%, however switch seems to be working without any problems and running 'show cpu input rate' command outputs ~1,7k pps - it's not much for it I perhaps... Switch handles routing between couple of subnets in 2 vlans (~12 subnets - it's about 100 desktops and ~200 linux servers in virtualized environment). Does have any ideas what's wrong?

Best Regards

[paolo bevilacqua]

Wrong forum, post in "small business switches". You can move your post using the Actions panel on the right.

[Tom Watts]

Hi Radoslaw, cn you please provide output of the follow-

show mac address-table count

show cpu input rate

show cpu utilization

show arp (parse the output, I'm only interested in # of entries)

show services tcp-udp

show log file

-Tom
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[rbolforski]

Hello Tom, thanks for reply. I pasted outputs from that commands on pastebin to make them and that thread more readable:

http://pastebin.com/h4jnskpV

It's night now in Poland so there is no people in our office, also that switch has been rebooted couple hours ago. I've just turned on logging (I had it off to lower cpu usage) maybe it catch something while next working day then I will paste it. CPU utilization is now lower - during normal working hours it's 100% all the time.

Best Regards

[Tom Watts]

Right now the switch looks okay but even the cpu at right now is 56% with not much happening.

I'd be curious to see all of those outputs during normal operations.

-Tom
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[rbolforski]

Hello,

http://pastebin.com/AHntZEHt

Above it's output from that commands in normal working hours in our office. There is just more traffic but nothing else seems to be different than outputs from night, however cpu utilization on that switch is hitting ceiling in my dc

Best Regards

[Tom Watts]

Radoslaw, I am thinking this may be normal operation. I am running different tests.

I opened 213 command prompts and pinged the switch SVI in layer 3 mode sending 1500 bytes and I was at 58% cpu utilization while sitting at 500 pps to the cpu. If I do something such as a speed test which my internet is 20 mbit download / 3 mbit upload, the cpu input increases up to 1400 PPS and the utilization hit nearly 90%

This is with my computer using the default gateway of the switch SVI.

If I put my computer back to receiving DHCP from my router and keep my pings running to the switch SVI, it is the same result. 500 PPS and 58%. If I run a speedtest with this condition the cpu utilization of the switch does not change nor does my packets per second.

This obviously indicates the switch as a default gateway ensures there is a route decision which increases the cpu usage of the switch. This also tells us that if the switch is only forwarding request it does not really hit the CPU at all.

Since I do not see any over flow errors or forwarding table errors I wouldn't pay any mind to the CPU information. If there's an actual usage problem then it would be worth investigating if the switch is not performing.

-Tom
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[rbolforski]

Thanks Tom for your attempt to solve my 'problem'. Next week I should get some brand new sg500's then I will check how that switch is displaying utilization in different configurations (maybe one subnet per vlan or something). Swich is working normally so I was a bit confused when I discovered that it display high cpu utilizaiton when it whan not really loaded.

[Tom Watts]

Hi Radoslaw, can you verify something for me?

How many vlans total do you have?

Do you have a "management" vlan and no data traffic passes on it?

As an example, vlan 1 is a default vlan and you have 2 other vlan that carries all traffic?

Or does your management vlan carry user traffic of a sort as well?

-Tom
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[rbolforski]

Hello Tom, sorry for late answer but I was offline for couple of days. Currently I have 3 vlans: 1 - mgmt, 300 - lan, 301 - wan. All user data traffic is sent via lan or wan vlan (depends on traffic type), management vlan is just for admin things such as ssh, snmp and others.

Best Regards