DHCP oddity



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?

--
-- Skylar Thompson (skylar@xxxxxxxxxxxxxx)
-- http://www.cs.earlham.edu/~skylar/

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Relevant Pages

  • Re: DHCP oddity
    ... I put dhcpd into debug mode and didn't get any error messages. ... interface was put into promiscuous mode? ...
    (freebsd-net)
  • Re: DHCP oddity
    ... > put dhcpd into debug mode and didn't get any error messages. ... interface was put into promiscuous mode? ...
    (freebsd-net)
  • Re: DHCP oddity
    ... 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. ... At a guess, dhcpd isn't using a PCAP/BPF filter to restrict itself to only paying attention to the traffic which it should care about, so it has to spend CPU in userland to process and discard all of the extra traffic. ... I suppose you need to pay attention to ICMP too, if you are going to ping-test IPs before assigning leases. ...
    (freebsd-net)