Re: [vox-tech] eth0 troubles

[Ken Bloom <kabloom@ucdaMAPSvis.edu>]

On Thu, Aug 12, 2004 at 01:04:01PM -0700, Karalius, Joseph wrote:
> 
> > -----Original Message-----
> > From: vox-tech-bounces@lists.lugod.org
> > [mailto:vox-tech-bounces@lists.lugod.org]On Behalf Of Ken Bloom
> > Sent: Thursday, August 12, 2004 12:38 PM
> > To: lugod's technical discussion forum
> > Subject: Re: [vox-tech] eth0 troubles
> > 
> > 
> > _______________________________________________
> > vox-tech mailing list
> > vox-tech@lists.lugod.org
> > http://lists.lugod.org/mailman/listinfo/vox-tech
> > 
> 
> > Is it possible that the DHCP server is only willing to give out IP
> > addresses to certain machines (based on MAC address for example), and
> > isn't willing to give out addresses to any machine that you might
> > decide to plug into the network?
> >
> > -- 
> 
> I doubt it. We have employees from around the world come visit our site and
> can get IP leases no problem.  I've set up Linux machines on our LAN without
> IT knowing about it and have gotten leases as well.
> 
> You bring up another question though.  When I run /etc/init.d/networking
> restart
> the output shows:
> 
> Listening on LPF/eth0/00:0d:56:93:83:34
> Sending on   LPF/eth0/00:0d:56:93:83:34
> Sending on   Socket/fallback/fallback-net
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 4
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 4
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 10
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 10
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 7
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 7
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 13
> DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 5
> No DHCPOFFERS received.
> No working leases in persistent database.
> 
> Exiting.
> 
> Failed to bring up eth0.
> done.
> 
> Does 'No DHCPOFFERS received. No working leases in persistent database.'
> mean that there was indeed a successful connection to the DHCP server but no
> leases available to that machine or would that message show up in any case
> where there was simply no response?

DHCP runs over UDP (when you run DHCP, the datagram has a source IP
address of 0.0.0.0, and uses a transaction number to identify which
host is intended to recieve and interpret the reply). This means that
DHCP is connectionless. You send out a packet, and hope for the best.
And you would have no way of differentiating the situation you see
here from situations where there is no DHCP server on the network, or
where congestion somewhere in the network causes your DHCPDISCOVER
request to get dropped by a congested router.

(Consequently, that's why DHCP makes several tries to connect - that
way if the first one meets with transient failure, then the others
have a chance of working)

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