how to get F12 to 'send host-name' in dhcp request?

[M. Milanuk]

Hello,

I have a couple virtual machines hooked together on a virtual LAN inside 
Virtualbox.  The server box has CentOS 5.4 running dnsmasq providing 
local name resolution, dns caching, and dhcp.  Specifically, it is 
configured so that when a client sends a dhcp request containing 'send 
host-name "demandred.local", dnsmasq will check /etc/hosts on the 
server, and give the requesting dhcp client the corresponding ip address 
listed in /etc/hosts.

I have three 'client' VMs: desktop installs of Ubuntu 9.10, Debian 
Lenny, and Fedora 12.

In Ubuntu 9.10, running Network Manager this was fairly simple: I set it 
to send a DHCP Client ID of 'asmodean', and voila! it gets the address 
10.0.0.2 as listed in the /etc/hosts on the gateway server box.

In Debian Lenny, I had to make a minor edit to /etc/dhcp3/dhclient.conf, 
basically creating a line that said 'send host-name "lanfear" and bam!, 
that machine got its ip address (10.0.0.4) exactly as listed in 
/etc/hosts on the server.

In Fedora 12, running Network Manager, with the name 'demandred' entered 
just as I did on the Ubuntu box... I get a random ip from the pool.  I 
*do not* get the ip that is associated with that name in the /etc/hosts 
file on the server, like the other two machines did.

I've checked the spelling, in the /etc/hosts file, in the 
/etc/dnsmasq.conf file, and on the F12 client.  Everything looks good. 
If I change the dnsmasq.conf file on the server to id the client by MAC 
address, then the F12 box gets its ip as intended.  But not if I just 
specify the client id in Network Manager.  I've looked, and because 
there *is* Network Manager, there doesn't seem to be a dhclient.conf 
anymore.  I've heard various rumors of there being interface specific 
variants, but so far I'm not having any luck finding out where the F12 
equivalent of dhclient.conf is.  One person mentioned 
/var/run/nm-dhclient-eth0.conf, which does contain 'send 
dhcp-client-identifier "demandred"; along with some comments that the 
file was created by Network manager and that line was added by it.

So... while I can 'make' this work (by including the MAC address) if I 
need it, I still am at a loss as to why it doesn't seem to be working 
*right*.  At this point I'm starting to wonder if the 'send 
dhcp-client-identifier "demandred" bit is getting to the dnsmasq server, 
or if its just not accepting it because its expecting 'send host-name...'?

Can someone help me out here?  This is driving me nutty.  How do I make 
F12 send the right request to the dhcp server?

TIA,

Monte

[Bill Davidsen]

M. Milanuk wrote:
>  On 12/17/2009 2:47 AM, Tom Horsley wrote:
> > On Wed, 16 Dec 2009 21:29:46 -0800
> > M. Milanuk wrote:
> >
> >> Can someone help me out here?  This is driving me nutty.  How do I make
> >> F12 send the right request to the dhcp server?
> >
> > Every distro seems to do this differently (sometimes each distro
> > changes between releases :-), but for fedora/redhat what has
> > always worked for me is to edit the ifcfg-eth0 script
> > and add:
> >
> > DHCP_HOSTNAME="whatever"
> >
> > to the parameters.
> >
>  
>  
>  Hello Tom,
>  
>  Thanks for the help.  I took a look in that script, and I see what 
>  you're talking about.  I may end up going that route in the end, or just 
>  editing the dnsmasq.conf file on the server to use dhcp-client-id 
>  instead of dhcp-host.
>  
>  In the mean time, its still bugging me as to what exactly is going on 
>  here.  On further inspection, the /var/run/nm-dhclient-eth0.conf files 
>  for both the F12 machine and the U9.10 machine are nearly the same they 
>  *both* have Network Manager adding the same line to the end ('send 
>  dhcp-client-identifier "demandred" '), but the file in U9.10 looks like 
>  they just copied over /etc/dhcp3/dhclient.conf (which they still have) 
>  into the NM file, with one line uncommented:
>  
>      send host-hame "<hostname>";
>  
>  I don't know if that gets expanded when the script is run to take the 
>  machines hostname and send it as part of the dhcp request, and thats why 
>  it gets the proper dhcp lease as it should, and F12 doesn't?
>  
>   From the sounds of things, it appears I'm going to have to learn a bit 
>  about wireshark and start trying to capture the network traffic when the 
>  client machines send their dhcp requests and see what is and isn't being 
>  sent.
>   
Learning wireshark and tcpdump are valuable goals for anyone who is getting into 
checking that network traffic is proper.

I thought I had taken the easy way out by just setting the MAC address of 
virtual machines so I can control the name and IP address in one place. Nothing 
I see in this thread makes me think there's a better way. ;-)

Having all the name/IP/MAC information in one place has made my life easier many 
times, both for administration and documentation.


-- 
Bill Davidsen <davidsen(a)tmr.com&gt;
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

[M. Milanuk]

On 12/17/2009 2:47 AM, Tom Horsley wrote:
>  On Wed, 16 Dec 2009 21:29:46 -0800
>  M. Milanuk wrote:
>
> > Can someone help me out here?  This is driving me nutty.  How do I make
> > F12 send the right request to the dhcp server?
>
>  Every distro seems to do this differently (sometimes each distro
>  changes between releases :-), but for fedora/redhat what has
>  always worked for me is to edit the ifcfg-eth0 script
>  and add:
>
>  DHCP_HOSTNAME="whatever"
>
>  to the parameters.
>  

Hello Tom,

Thanks for the help.  I took a look in that script, and I see what 
you're talking about.  I may end up going that route in the end, or just 
editing the dnsmasq.conf file on the server to use dhcp-client-id 
instead of dhcp-host.

In the mean time, its still bugging me as to what exactly is going on 
here.  On further inspection, the /var/run/nm-dhclient-eth0.conf files 
for both the F12 machine and the U9.10 machine are nearly the same they 
*both* have Network Manager adding the same line to the end ('send 
dhcp-client-identifier "demandred" '), but the file in U9.10 looks like 
they just copied over /etc/dhcp3/dhclient.conf (which they still have) 
into the NM file, with one line uncommented:

	send host-hame "<hostname>";

I don't know if that gets expanded when the script is run to take the 
machines hostname and send it as part of the dhcp request, and thats why 
it gets the proper dhcp lease as it should, and F12 doesn't?

 From the sounds of things, it appears I'm going to have to learn a bit 
about wireshark and start trying to capture the network traffic when the 
client machines send their dhcp requests and see what is and isn't being 
sent.

Thanks,

Monte

[Tom Horsley]

On Wed, 16 Dec 2009 21:29:46 -0800
M. Milanuk wrote:

>  Can someone help me out here?  This is driving me nutty.  How do I
> make 
>  F12 send the right request to the dhcp server? 
Every distro seems to do this differently (sometimes each distro
changes between releases :-), but for fedora/redhat what has
always worked for me is to edit the ifcfg-eth0 script
and add:

DHCP_HOSTNAME="whatever"

to the parameters.