[c-nsp] arp timeout issues

Ed Butler ed.butler at rapidswitch.com
Mon Feb 26 04:51:57 EST 2007


Yes, when the ARP times out we see this:

sh ip cef event | in 1.2.3.4
1y5w:  [Default] 1.2.3.4/32'08 FIB remove (flagged)     [OK]
1y5w:  [Default] 1.2.3.4/32'08 FIB remove (deleted)     [OK] 


Regards,

Ed Butler
RapidSwitch Ltd
DDI: 020 7106 0731

RapidSwitch Ltd, Sovereign House, 227 Marsh Wall, London, E14 9SD

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-----Original Message-----
From: Rodney Dunn [mailto:rodunn at cisco.com] 
Sent: 25 February 2007 18:16
To: Ed Butler
Cc: Cisco-NSP Mailing List
Subject: Re: [c-nsp] arp timeout issues

I don't know about those switches but can you see if there is a 'sh ip
cef event' and see if the adj is being updated when the arp refresh
happens?

I wonder if the hw adj is being updated and while we lock the adjacency
to update it we don't switch packets to it.

Have you put a sniffer on there to make sure the packets are not going
out?


On Sat, Feb 24, 2007 at 08:07:30PM -0000, Ed Butler wrote:
> Fairly standard set up; stack of 3750s running OSPF to 6500s. On the 
> 3750s there are a number of SVIs, with "arp timeout 300" set on them.
> The same VLANs have a MAC againg time of 5 minutes too.
> 
> The behaviour we are seeing is that every six minutes (not 5) traffic 
> to a host on the SVI will die for 500ms or so, and this coincides with

> the ARP entry being refreshed. CPU usage on the 3750 stack averages
15-20%.
> 
> We have a number of similar set up that don't replicate this problem.
> Has anyone seen similar and can recommend a course of action? 
> Hopefully something more sophisiticated than simply increasing the ARP
timeout!
> 
> Regards,
> 
> Ed Butler
> RapidSwitch Ltd
> DDI: 020 7106 0731
> 
> RapidSwitch Ltd, Sovereign House, 227 Marsh Wall, London, E14 9SD
> 
> This email message is intended only for the addressee(s) and contains 
> information that may be confidential and/or copyright.  No 
> representation is made that this email or any attachments are free of 
> viruses. Virus scanning is recommended and is the responsibility of 
> the recipient. RapidSwitch Ltd is registered in England & Wales
Company No.
> 04535693, Registered Address: 3 Beacon Mews, South Road, Weybridge, 
> KT13 9DZ. VAT Registration No. GB 794 3811 96. All prices exclude VAT 
> unless otherwise stated. Quotations valid for seven days.
> 
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