dhcpcd-discuss

Hi Kenny

On 19/02/2018 04:43, Kenny Napier wrote:
> The host is instructing the DHCP server my hostname is 'KensDevice' via 
> Option 81.
> Then the server responds to the host via option 81 in the Offer -  your 
> FQDN is actually dhcp-10-0-0-12.mycompany.com 
> <http://dhcp-10-0-0-12.mycompany.com>
> In this situation I have my own code that honors this change and sets 
> the hostname of the device to 'dhcp-10-0-2'.
> This is what the server updated in DNS.  I can use it to ping/reach the 
> device but not the name I first reported 'KensDevice'.
>
> > > It sounds like your node already knows it's hostname, so this is just for getting the DHCP server to update DNS yes?
> *
> *
> Correct .. the reason I am using the 'fqdn=both' option in dhcpcd is so 
> it will report back via the flags if it is willing to do the update or not.
> If it says it will not do the update I have another package that will 
> attempt to do its own DNS update.

What package do you use? Maybe it's something I could include as a 
generic hook in dhcpcd.

Maybe this package could update DNS to add KensDevice as an alias to the 
A record to work around the buggy DHCP server?

> I agree dhcpcd is correctly following the RFC by not sending both options.
> My goal in asking the question was to see if this is a issue others have 
> seen.   Perhaps my server is just misconfigured.
> At the moment I have not got past my IT bureaucracy to find out exactly 
> what type of server software is in use.

No-one has reported this behavior before.
Because the server supports FQDN I would guess the error is on the DHCP 
server.

> **
> This conversation I found using this 'infoblox' software is the closest 
> I have found to what I am experiencing.
> https://community.infoblox.com/t5/DNS-DHCP-IPAM/Generate-Hostname-if-not-Sent-by-Client/td-p/5061
>
> They discuss how the server conf file uses this instruction to pick the 
> auto generated name.
>
> /ddns-hostname = pick ( option fqdn.hostname,option host-name,
> concat *("dhcp-",binary-to-ascii(10,8,"-", leased-address)))*/
> */
> /*
>
> It would be nice if they had similar instructions that indicate how they 
> decide if the host name was omitted by the client or not.

My understanding from the above config statement is that the hostname 
would be one of three things from that statement, picking the first non 
blank entry - so FQDN option hostname part, hostname option, string 
based on leased address.

Now, the problem might stem from dhcpcd encoding the FQDN hostname as a 
DNS label and NOT as a text string. This is because text strings where 
supported in early drafts, but deprecated before it became an actual 
RFC. Some ISC dhcpd server versions do not like DNS label encoding in 
the FQDN hostname.
However, the encoding bit is set correcting in dhcpcd and the supporting 
server HAS to support it as per the RFC.

Roy