Unreliable LTSP DHCP server: No DHCP offers received on client

[John Hupp]

[Posting this for the group for the revised focus of the question......]

OK, interesting.

But indulge me in some further probing.  /usr/sbin/dhcpd is an 
alternative to the isc-dhcp-server set up under LTSP?  I ask that 
because when I run the long /usr/sbin/dhcpd command on a different LTSP 
test server that boots clients reliably (Lubuntu), it notes that another 
DHCP server is already running.

Another point of interest: On the problematic Ubuntu LTSP server, if I 
first "sudo service isc-dhcp-server start" to successfully start the 
service (much as I noted in the original post), then the output for the 
long /usr/sbin/dhcpd command includes:
     Listening on LPF/eth0/00:50:04:e2:4e:48/192.168.0.0/24
     Sending on LPF/eth0/00:50:04:e2:4e:48/192.168.0.0/24

     Sending on Socket/fallback/fallback-net

And the LTSP client will boot.

I wondered why isc-dhcp-server fails to start during bootup, butI could 
manually start it post-boot, at which point the LTSP client will 
successfully boot.  And why could I start isc-dhcp-server manually if 
there were a missing configuration.

Here's what I did next: Start the client first, then start the server.  
IT WORKS!!

Actually, unless the timing of the startups is right, the client fails 
to PXE boot on its first attempt.  But then restart the client and it 
works!!

Here is what I think is going on: In these little 2-machine networks, 
I'm connecting one server and one client via crossover cable rather than 
with a switch.  (I didn't tell you that, did I?)  But isc-dhcp-server 
apparently won't start on the Ubuntu server unless networking has 
detected that the LTSP interface is connected to a network.

There is still the live question of why my Ubuntu LTSP server requires 
this and the Lubuntu server does not.  Actually, I have two Lubuntu 
servers, and they both will work without starting the client first, at 
least on the combinations of servers and clients I have tested.

So even if my understanding is correct and provides a clumsy 
work-around, someone can still shed some very helpful light on the finer 
mechanisms, and whether I can configure the Ubuntu server so that 
isc-dhcp-server is ready to go even if I have not started the client first.

Thanks, Stéphane, for working the problem with me to date, and providing 
useful impetus.

On 8/22/2012 9:55 PM, Stéphane Graber wrote:
> On 08/22/2012 08:15 PM, John Hupp wrote:
>> A good guess about -q.  OK, that yields:
>>
>> Wrote 6 leases to leases file.
>>
>> No subnet declaration for lxcbr0 (10.0.3.1).
>> ** Ignoring requests on lxcbr0.  If this is not what you want, please
>> write a subnet declaration in your dhcpd.conf file for the network
>> segment to which lxcbr0 is attached.**
>>
>> No subnet declaration for eth1 (10.0.0.8).
>> ** Ignoring requests on eth1.  If this is not what you want, please
>> write a subnet declaration in your dhcpd.conf file for the network
>> segment to which lxcbr0 is attached.**
>>
>> Not configured to listen on any interfaces!
> Well that last line tells you what the problem is, none of your
> interfaces match the configuration in the DHCP server.
>
> You must have an interface in at least one subnet defined in dhcpd.conf
> for it to start.
>
>
>> -----------------------
>>
>> Perhaps useful to know at this point: On my two-interface setup, eth1 is
>> the outward-facing interface, and eth0 is the LTSP interface.  Both were
>> configured via the Network Connections interface.
>>
>> And perhaps worth repeating here is my initial observation that
>> everything works once I restart isc-dhcp-server.
>>
>>
>> On 8/22/2012 7:09 PM, Stéphane Graber wrote:
>>> On 08/22/2012 06:42 PM, John Hupp wrote:
>>>> I got no output from that command string, and I found that on this
>>>> system /run/dhcp-server/dhcpd.pid does not exist - that is an empty folder.
>>> Ah, right, try: (still on one line)
>>> sudo /usr/sbin/dhcpd -f -4 -pf /run/dhcp-server/dhcpd.pid -cf
>>> /etc/ltsp/dhcpd.conf
>>>
>>> My guess is that the -q was making any error/informational message go away.
>>>
>>>> On 8/22/2012 4:57 PM, Stéphane Graber wrote:
>>>>> On 08/22/2012 04:38 PM, John Hupp wrote:
>>>>>> Thanks.
>>>>>>
>>>>>> /var/log/upstart/isc-dhcp-server.log does not exist, but
>>>>>> isc-dhcp-server6.log does (perhaps related to the fact that this is an
>>>>>> LTSP DHCP server and not a regular DHCP server?).
>>>>>>
>>>>>> Its contents:
>>>>>>
>>>>>>      /etc/dhcp/dhcpd6.conf does not exist! - Aborting...
>>>>>>      Please create and configure /etc/dhcp/dhcpd6.conf to fix the problem.
>>>>>>      isc-dhcp-server6 stop/pre-start, process 1094
>>>>>>
>>>>>> But very interestingly, on another server for which the LTSP clients
>>>>>> boot reliably, isc-dhcp-server6.log has the same contents!
>>>>> That's the expected content for isc-dhcp-server6.log for a network
>>>>> without IPv6.
>>>>>
>>>>> Try running (one line):
>>>>> sudo /usr/sbin/dhcpd -f -q -4 -pf /run/dhcp-server/dhcpd.pid -cf
>>>>> /etc/ltsp/dhcpd.conf
>>>>>
>>>>> >From a shell, that should tell you what's failing.
>>>>>
>>>>>> On 8/22/2012 3:21 PM, Stéphane Graber wrote:
>>>>>>> On 08/22/2012 03:02 PM, John Hupp wrote:
>>>>>>>> I have a couple small LTSP networks set up for testing.  On the network
>>>>>>>> with Edubuntu 12.04, the LTSP client boot regularly fails at step one of
>>>>>>>> the PXE boot with the message: "DHCP ..... No DHCP or proxyDHCP offers
>>>>>>>> were received."
>>>>>>>>
>>>>>>>> Restarting the isc-dhcp-server service always works, but something about
>>>>>>>> the boot process regularly causes it to fail to start.  The restart
>>>>>>>> command output:
>>>>>>>>      stop: Unknown instance:
>>>>>>>>      isc-dhcp-server start/running, process (pid goes here)
>>>>>>>>
>>>>>>>> Dmesg includes these lines:
>>>>>>>>      init: isc-dhcp-server main process ended, respawning
>>>>>>>>      init: isc-dhcp-server main process (pid goes here) terminated
>>>>>>>>      init: isc-dhcp-server respawning too fast, stopped
>>>>>>>>
>>>>>>>> Is anyone familiar with this problem?
>>>>>>> Look in /var/log/upstart/isc-dhcp-server.log for details.
>>>>>>>
>>>>>>>




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