DHCPREQUEST of <null address>
Glenn Satchell
Glenn.Satchell at uniq.com.au
Sun May 4 13:07:48 UTC 2008
>Date: Sun, 04 May 2008 13:31:45 +0100
>From: Alan Jenkins <aj504 at cs.york.ac.uk>
>To: dhcp-users at isc.org
>Subject: DHCPREQUEST of <null address>
>
>Before I start: my network configuration is somewhat awkward. I'll
>explain it for completeness so I'm not accused of holding anything back,
>but I'm only really interested in these strange DHCPREQUESTs (see subject).
>
>Second point: I'm using Ubuntu's dhclient. I will retry using the
>latest version without any potentially malign distro patches. It'll
>take a bit longer though and I've just nailed down the issue, so I'm
>posting here with details as a first step. Maybe my problem is
>familiar, or maybe it'll go away if I use the pure version and provide a
>little more hard evidence that the distro pacakges suck :-).
>
>OK, I'm in university dorms with ethernet and an authentication
>mechanism which is handled by wpa_supplicant. I hacked up some
>network-manager scripts so it all works nicely. Admittedly, sometimes
>it starts up confused, and I'm assigned an "unauthenticated" IP address
>which starts "172." (authenticated addresses start with "144.") and my
>net access doesn't work. But I can just reconnect a couple of times
>(by kicking network-manager) and it eventually gets an authenticated IP
>address.
>
>Back to these strange messages, "DHCPREQUEST of <null address>".
>
>Does this mean that dhclient has run out of valid leases? This type of
>DHCPREQUEST is happening very frequently for me - suggesting that
>there's a problem where dhclient is failing to renew the current lease
>before it expires. [For whatever reason. No criticism of dhclient
>implied].
>
>But it's not even that. Have a look at this log:
>
>May 4 11:52:18 alan-eeepc last message repeated 2 times
>May 4 11:52:36 alan-eeepc dhclient: DHCPREQUEST of <null address> on
>eth1 to 255.255.255.255 port 67
>May 4 11:52:36 alan-eeepc dhclient: DHCPACK of 144.32.61.4 from
>144.32.129.66
>May 4 11:52:36 alan-eeepc NetworkManager: <info> DHCP daemon state is
>now 3 (renew) for interface eth1
>May 4 11:52:36 alan-eeepc dhclient: bound to 144.32.61.4 -- renewal in
>1579 seconds.
>May 4 12:18:55 alan-eeepc dhclient: DHCPREQUEST of <null address> on
>eth1 to 144.32.129.66 port 67
>May 4 12:19:19 alan-eeepc last message repeated 3 times
>May 4 12:20:15 alan-eeepc last message repeated 3 times
>May 4 12:21:26 alan-eeepc last message repeated 5 times
>
>We see that the renewal time is about 25 minutes, and the <null address>
>requests happen at the renewal time. So dhclient thinks the lease has
>expired as soon as it tries to renew it! But look at the expiry time in
>the leases file:
>
>lease {
> interface "eth1";
> fixed-address 144.32.61.4;
> option subnet-mask 255.255.255.0;
> option routers 144.32.61.1;
> option dhcp-lease-time 2840;
> option dhcp-message-type 5;
> option domain-name-servers 144.32.128.228,144.32.129.66;
> option dhcp-server-identifier 144.32.129.66;
> option domain-name "york.ac.uk";
> renew 0 2008/5/4 12:08:23;
> rebind 0 2008/5/4 12:26:41;
> expire 0 2008/5/4 12:32:36;
>}
>
>So the lease shouldn't have expired that quickly.
>
>I think this is causing a certain amount of difficulty; the DHCP server
>isn't responding until... well, in this sequence the next DHCPACK is at
>12:45. Really. Which doesn't make any sense, but then neither does my
>"unauthenticated address" problem. I do think the DHCP server generally
>sucks, but that doesn't really explain what dhclient is doing here.
>
>Alan
I've got no idea on the <null address>.
Most dhcp clients attempt to renew the lease about 50% of the way
through. This lets them keep the same IP address for a long time, even
if the lease time is short.
regards,
-glenn
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