From owner-freebsd-net@FreeBSD.ORG  Tue Dec 27 13:06:19 2005
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Date: Tue, 27 Dec 2005 13:06:14 +0000
From: Brian Candler <B.Candler@pobox.com>
To: Skylar Thompson <skylar@cs.earlham.edu>
Message-ID: <20051227130614.GA3148@uk.tiscali.com>
References: <43B03332.2010904@cs.earlham.edu>
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Cc: freebsd-net@freebsd.org
Subject: Re: DHCP oddity
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On Mon, Dec 26, 2005 at 12:15:14PM -0600, Skylar Thompson wrote:
> While doing some network stress-tests from a dual-CPU x86 FreeBSD 5.4 
> server, I noticed that a "ping -f" drives dhcpd's CPU usage way up. I 
> put dhcpd into debug mode and didn't  get any error messages. I then ran 
> dhcpd with strace, and saw loads of these messages when I started the 
> ping flood:
> 
> select(8, [?], [?], [?], NULL)          = 1 ()
> gettimeofday({...}, NULL)               = 0
> recvfrom(4, 0xbfbfe090, 1500, 0, {...}, [?]) = 84
> select(8, [?], [?], [?], NULL)          = 1 ()
> gettimeofday({...}, NULL)               = 0
> recvfrom(4, 0xbfbfe090, 1500, 0, {...}, [?]) = 84
> 
> Does anyone know why this would happen?

Were you running tcpdump or similar at the same time, such that the
interface was put into promiscuous mode?

Check using ifconfig that it is not (i.e. there is no PROMISC flag shown)