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NeDi Software Specific => Discovery => Topic started by: Falcon8484 on February 24, 2009, 03:41:15 PM

Title: Switch discovery load a lot the CPU(switch)
Post by: Falcon8484 on February 24, 2009, 03:41:15 PM
Hi !

I'm trying to light my discovery because NeDi load my switch CPU ! The normal usage is 8% with the discovery he fly to 70% !

I found that NeDi take a wild trying to match MAC adress of all my network and Vlan... There's a solution to match the MAC adress with Vlan for just the one behind my switch ?

Thanks for your help
Title: Re: Switch discovery load a lot the CPU(switch)
Post by: rufer on February 25, 2009, 09:01:17 AM
What model of switch?
I never had such a problem with Cisco Catalyst.

Greetings
Rufer
Title: Re: Switch discovery load a lot the CPU(switch)
Post by: Falcon8484 on February 25, 2009, 09:07:40 AM
It's a Cisco Catalyse 3750...

I wasn't expecting that ! Do you have a idea ?

Thanks
Title: Re: Switch discovery load a lot the CPU(switch)
Post by: rickli on February 25, 2009, 05:51:53 PM
How many vlans do you have configured on that thing?
Title: Re: Switch discovery load a lot the CPU(switch)
Post by: Falcon8484 on February 26, 2009, 08:10:20 AM
We have 200 Vlans ... Do you thing it's the reason ?

In Nedi it show 8% but we I check the value directly on the switch it goes up to 70% (by Sabbix)... I saw NeDi take most of the time, matched the MAC address with the Vlan... 
Title: Re: Switch discovery load a lot the CPU(switch)
Post by: rufer on February 26, 2009, 09:15:04 AM
Which IOS version do you have? The old 3750 IOS are quite buggy.
So the CPU usage goes up to 70% momentarly when Nedi discovers the switch? I wouldn't worry too much about that, after your first post I thought that it is on 70% all time. Read the Cisco release notes for your IOS, often it is noted that SNMP can consume a lot of CPU. But at least with current IOS this doesn't degrade switch performance.

If you really worry about this, add a custom rate limiter for SNMP packets (but this will probably slow down Nedi discovery).

Greetings
Rufer
Title: Re: Switch discovery load a lot the CPU(switch)
Post by: rickli on March 01, 2009, 02:00:41 PM
The problem is in order to read forwarding tables on Cisco switches NeDi needs to do something calle vlan community indexing. Effectively NeDi walks the forwarding mib with each vlan appended to the community (e.g. public@1, public@2 and so forth) in order to collect all nodes. You typically see a lot of warnings related to empty forwarding tables in this case as well.

Because of this I implemented the CLI alternative for getting forwarding tables. NeDi then uses telnet or SSH to get the info via CLI. As I just got a donation in regards to this topic I'm going to write some more documentation here:http://www.nedi.ch/doku.php?id=discovery:discovery (http://www.nedi.ch/doku.php?id=discovery:discovery)