dhcpcd-discuss

Hi Roy,
 
On Thursday, May 01, 2014 11:44 PM, Roy Marples wrote:
> Hi David
> 
> On 02/05/2014 0:04, David Hauck wrote:
>> I just received a report about something I thought I'd verified a
>> couple months ago. However, I've now verified via Wireshark that my
>> current v6.1.0 dhcpcd client isn't sending option 12 (hostname) in
>> its initial DISCOVER packet, while the same configuration in v6.0.5 does.
>> 
>> Here's the configuration file:
>> # Inform the DHCPv4 server of our hostname for DDNS.
>> # This has been superceded by the FQDN option below, but is included
>> # by default for servers which do not understand it.
>> hostname
>> 
>> # Inform the DHCP server of our hostname for DDNS # and/or query for
>> what it should be.
>> fqdn
>> 
>> # Be sure to handshake our vendor code (for interoperability with
>> NNIT).
>> vendor 01,"0"
>> 
>> There seems to be some interaction between hostname and fqdn options
>> in 6.1.0: when I comment out 'fqdn' above I see option 12 (hostname)
>> show up in the DISCOVER. So there seems to be some weird interaction
>> between hostname and fqdn in 6.1.0 (this same interaction does not
>> seem to be present in 6.0.5 - i.e., the above configuration works
>> fine wrt option 12).
>> 
>> Any explanation for why this might be?
> 
> I had to look some stuff up as to why!
> 
>  From RFC4702
> 3.1. Interaction with Other Options
> 
> 
>     Other DHCP options MAY carry data that is related to the Domain Name
>     field of the Client FQDN option.  The Host Name option [12], for
>     example, contains an ASCII string representation of the client's host
>     name.  In general, a client does not need to send redundant data, and
>     therefore clients that send the Client FQDN option in their messages
>     MUST NOT also send the Host Name option.

Well, that's pretty clear :)!

OK, I think I had enabled both options because some servers needed hostname and some servers needed fqdn. I wonder if there is a way to only provide one option depending on which server the dhcpcd client is talking too (I think you answered this below)? If not, I'll need to work with the servers that only understand hostname to see if they can be configured/upgraded to understand the newer fqdn option.

Thanks,
-David

> Documented in the code here now.
> http://roy.marples.name/projects/dhcpcd/fdiff?v1=40faa5f47107e2a2&v2=e
> aa54368628b9719&sbs=1
> 
> 		/*
> 		 * RFC4702 3.1 States that if we send the Client FQDN option
> 		 * then we MUST NOT also send the Host Name option.
> 		 * Technically we could, but that is not RFC conformant and
> 		 * also seems to break some DHCP server implemetations such as
> 		 * Windows. On the other hand, ISC dhcpd is just as non RFC
> 		 * conformant by not accepting a partially qualified FQDN.
> 		 */
> 
> Also see https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1088682
> 
> This is one RFC bit I disagree with as the client has no way of
> knowing if the server supports the FQDN option, but I don't think
> there's much I can do about it.
> 
> Thanks
> 
> Roy