[Novalug] getting linux hosts to bind their name to DHCP?

James Ewing Cottrell 3rd JECottrell3@Comcast.NET
Thu Sep 2 22:20:35 EDT 2010


  First, let me deal with Peter's objection. The key word here is 
"dictate". The correct word is "request". There is nothing in the DHCP 
spec that forces a DHCP server to assign the requested name, or even 
assign an address at all. That is up to the Policy of the DHCP Server.

In other words, your Objection has been duly noted and incorporated into 
the spec. You've Already Won.

Likewise, the DNS Server can be configured to only accept updates from 
the DHCP Server. I hear that in the M$ world, that clients generally do 
the update rather

As for Jason's observation, I believe that strictly speaking, leases are 
an IP/MAC pair. Names are secondary. In any case, it seems that eiether 
or both of the client and server are deficient. The client should have 
recorded its lease somewhere, and
attempt to rebind. If the client can determine that it is on the same 
subnet, it need not even contact the Server. But if it does
ask, the Server must answer with the existing lease and do nothing else, 
other than optionally extending the lease.

It also sounds like the coordination between DHCP and DNS could be better.

JIM

In other words, your Objection has been duly noted and incorporated into 
the spec. You Already Won.

On 9/2/2010 3:46 PM, Jason Kohles wrote:
> Generally the DHCP server has to be specifically configured to allow the lease to be taken over by another host, by default the host can only request the name it already had or a name that isn't in use.  On my OS X workstation for example, if I manage to crash the machine so I have to reboot it without releasing the lease then it won't get it's normally assigned name of jkohles-macpro, and will instead show up on the network as jkohles-macpro-1, and then once the lease expires I can get it to switch back.
>
> On Sep 2, 2010, at 3:19 PM, Peter Larsen wrote:
>
>> It always strikes me as a security issue to allow the clients to dictate
>> the host names. Rather easy to take over a www or similar system address
>> that way. Usually I let dhcpd and bind negotiate the client host names.
>> I don't let the client tell the host what names they have.
>>
>> Regards
>>   Peter Larsen
>>
>> On Thu, 2010-09-02 at 12:46 -0400, James Ewing Cottrell 3rd wrote:
>>> On 9/1/2010 10:15 PM, Theodore Ruegsegger wrote:
>>>> Scott wrote:
>>>>> In a post I made a few days back I mentioned that I was having problems
>>>>> with my FIOS router not accepting the hostname for it's DNS, when my
>>>>> linux hosts boot DHCP. They show up as new-host, new-host-1, etc.
>>>>>
>>>>> I did a quick search and it recommends adding the DHCP_HOSTNAME keyword
>>>>> to the ifcfg-eth<?>   file in the /etc/sysconfig/network-scripts dir
>>>>> (since these are RH/Fedora installs).
>>>>>
>>>>> Unfortunately this doesn't seem to work either? What am I missing?
>>>> Not sure whether this is universal or just for Debian and derivatives,
>>>> but I add a line to
>>>> /etc/dhcp3/dhclient.conf:
>>>>
>>>> send host-name "basil";
>>>>
>>>> The file even comes with commented out examples of various options, e.g.,
>>>> #send host-name "andare.fugue.com";
>>>>
>>>> hth
>>>> Ted
>>> It's universal in a fuzzy sense. On RH systems, I have a file named
>>> /etc/dhclient-eth0.conf that contains the
>>> 'send host-name "mypc.example.com";' line. This is the inner, or
>>> low-level configuration file. The outer, or high level configuration
>>> file is indeed /etc/sysconfig/networking-scripts/ifcfg-eth0, and the
>>> controlling line looks like
>>>
>>> DHCP_HOST=mypc.example.com
>>>
>>> and can be set via system-config-network. Of course, your favorite
>>> editor works too.
>>>
>>> JIM
>>>
>>> _______________________________________________
>>> Novalug mailing list
>>> Novalug@calypso.tux.org
>>> http://calypso.tux.org/mailman/listinfo/novalug
>>
>> -- 
>> Best Regards
>>   Peter Larsen
>>
>> Wise words of the day:
>> Actually, typing random strings in the Finder does the equivalent of
>> filename completion.
>> 	-- Discussion on file completion vs. the Mac Finder
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