[klibc] Bug#594638: klibc-utils: ipconfig assumes dhcp server is nameserver

[Vagrant Cascadian]

On Tue, Aug 31, 2010 at 02:21:56PM +0200, maximilian attems wrote:
> On Fri, 27 Aug 2010, Vagrant Cascadian wrote:

> > ipconfig apparently assumes that the dhcp server's ip address is the
> > nameserver when dhcp gives it no nameservers, dhcp gives the nameserver
> > 0.0.0.0, or the nameservers are not ip addresses (i.e. ns1.example.org).
> > while these scenarios are probably not extremely common, i'm not sure
> > this is a good default with no way to disable it. 
> 
> hmm, several questions at mind, what do you mean my "dhcp gives the
> nameserver" is this the ISC dhcp 3 client?

in this case, i tested with isc-dhcp-server, with the domain-name-servers option:

  option domain-name-servers ns1.example.org, ns2.example.org;

or
  
  option domain-name-servers 0.0.0.0;

or having no domain-name-servers specified.

though i suspect any DHCP server configured with one of the above mentioned
cases would trigger the issue in ipconfig.

i know the udhcpc client doesn't respond in the same way, haven't yet tested
isc-dhcp-client.

> is that really a sensible thing to do?
> what do standards say (aka RFC's pointers)?

i don't know off the top of my head... i'll look into it a bit more.
 
> we could set it to the public available google server,
> as this one might be better working as this guess of
> the el cheapy router box?

without reading RFC's, it doesn't necessarily seem invalid to me to have no
nameservers on a network, and supplying a guessed default may cause problems.
  
> > it prints out the message:
> > 
> >   IP-Config: eth0 guessed nameserver address 192.168.0.1
> 
> according to git history this was added on day 0 of ipconfig,
> not that this would justify it.

i didn't notice the issue till recently, when we configured ltsp to actually
use the nameserver configuration that ipconfig recieves from the DHCP reply
(Debian Bug #593770), and decided to play around with some unusual
corner-cases...

thanks for working on ipconfig!

live well,
  vagrant