Need explanations about server-name, next-server...

[Glenn Satchell]

>Date: Mon, 5 Mar 2007 18:01:02 +0100
>From: Jeremie Le Hen <jeremie at le-hen.org>
>To: dhcp-users at isc.org
>
>Hi list,
>
>On Sun, Mar 04, 2007 at 08:49:40PM +0100, Jeremie Le Hen wrote:
>> I have been looking for PXE HOWTOs and I saw numerous options that
>> seems to overlap themselves.  I've read what I could in dhcpd.conf(5)
>> manpage and glanced at RFC1533 as well but I'm still bewildered.
>> 
>> Some setups use "server-name", some others "next-server".  I even
>> saw "option tftp-server-name" sometimes.  Most of the time they
>> all have the same value.
>> 
>> I think that "server-name" is just a string identifying the DHCP
>> server, though I don't really understand the purpose of such an option.
>> The "next-server" option seems to describe the IP address (or
>> FQDN) or the TFTP server.
>> 
>> Am I right ?  In this case, what's the usefulness of
>> "option tftp-server-name" ?
>> 
>> I would be glad of someone could point out the reference or a
>> description for this.
>
>I think I succeeded to gather enough informations about this to
>reply myself, for the record.
>
>* "server-name" is just an informative name, giving the real name
>  of the DHCP server.

man dhcpd.conf

       server-name name ;

       The server-name statement can be used to inform the client
       of the name of the server from which it is booting.   Name
       should be the name that will be provided to the client.

My reading is that this is the name of the dhcp server.

>* "next-server" is the ``address of the server to use in the next step
>  of the client's bootstrap process''.  No protocol is specified and
>  hence I assume this is implementation-defined.

man dhcpd.conf

       next-server server-name;

       The next-server statement is  used  to  specify  the  host
       address  of  the  server  from which the initial boot file
       (specified in the filename statement)  is  to  be  loaded.
       Server-name  should  be  a  numeric IP address or a domain
       name.

The protocol could be tftp, or ftp or nfs or something else. It is
something that is configured on the appropriate server knowing the
behaviur of the client. Often, however, it does use tftp. Whatever
follows once the initial boot file has been downloaded is up to the
client. It is asumed that the client either knows what to do next, or
that information is in the bootfile.

>* "tfp-server-name" is just an informative name as well, when the
>  "sname" (server-name) field has been used for DHCP options.

man dhcp-options

     option tftp-server-name text;

       This option is used to identify a TFTP server and, if sup-
       ported  by  the client, should have the same effect as the
       server-name declaration.   BOOTP clients are  unlikely  to
       support  this  option.  Some DHCP clients will support it,
       and others actually require it.

This is carried as a different dhcp option number, so it is different
to next-server. It is specific to tftp. Not all clients can use this
option.

For a full description of these concepts you could refer to RFC2131 -
this is the dhcp RFC. However, the names are specific to ISC dhcp
server.

HTH.

regards,
-glenn