"DHCP set the hostname"

Tim Peiffer peiffer at umn.edu
Thu Mar 1 11:50:38 UTC 2007

It matters only in 2 cases.  In the netbios context, a duplicate name is 
as bad as a duplicate IP address.  In the DHCP informs Dynamic DNS, I 
think that only the last update will win the duplicate name issue.  In 
the long run, if a name doesn't leak out of the box, then the name is 
private..  think RFC1918 private IP space. If there is multiple use of 
an IP, it is ok as long as the address is not leaked into the public space.

With use of DDNS and the large predominance of the use of SRV records to 
promote services, I can see the name leaking out fairly easily albeit in 
error.  How many people really turn off services they don't need, like 
file sharing, or print sharing?
I can see it easy on the LAN for situations to arise where someone 
broadcasts for printer service resolution, and his neighbor says sure..  
a printer is located at 'joes printer'@localhost.localdomain.

I do have approximately 80,000 devices that are maintained by people 
whose qualifications to do so span the spectrum.  That  said, I have not 
really seen any of the above in the last 10 years.


Carl Karsten wrote:
> Thanks.  Not quite as definitive as I had hoped for, but good enough.
> Next Q: what are the implications of multiple machines with the same hostname? 
> In other words: does it matter if they are all left set to localhost.localdomain?
> Carl K
> Tim Peiffer wrote:
>> A read of the manual page for dhcp-option(5) and dhclient-script(5) is 
>> useful.  An excerpt from the man page says:
>>        option host-name string;
>>           This option specifies the name of the client.  The name may  
>> or  may
>>           not be qualified with the local domain name (it is preferable 
>> to use
>>           the domain-name option to specify the domain name).   See  
>> RFC  1035
>>           for  character  set  restrictions.   This  option is only 
>> honored by
>>           dhclient-script(8) if the hostname for the  client  machine  
>> is  not
>>           set.
>> The use of the host-name specified is optional and depends upon how the 
>> client is configured.  Now the next logical question, is how does this 
>> work in Winderz?
>> Carl Karsten wrote:
>>> host-name is optional, right?
>>> I am sure I know the answer, but can't find support for it.
>>> This is for a olpc bugreport that goes like this:
>>> cjb: doesn't DHCP set the hostname, though?
>>> CarlFK: it can, but from what I have seen dhcp doesn't always happen
>>> CarlFK: and it isn't guaranteed
>>> cjb: if dhcp doesn't happen, we're not on a network and don't care that we don't 
>>> have a unique hostname.
>>> Carl K

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