PVE 9.2-1 | Automated Installation | ISO installer dhclient does not request DHCP option 119 (domain-search) which prevents auto install using DNS

[MJ_UI]

Hello,

tl;dr: @ProxmoxVE staff: Could you please add option 119 (domain-search) to the /etc/dhcp/dhclient.conf in your official ISO?

I'm using proxmox-ve_9.2-1.iso and followed the official documentation for Automated Installation to use answer files.
I've prepared an ISO image using the proxmox-auto-install-assistant and set the fetch method (--fetch-from) to http, without explicit --url, to retrieve the URL and Fingerprint via DNS txt records: proxmox-auto-installer.{search domain}
The DNS record is correctly set, validated via dig -t txt proxmox-auto-installer.my-own-search-domain.org
The DHCP server is configured correctly, as it serves option 119 (domain-search), but only when option 119 is requested explicitly via the DHCP client's Parameter Request List.
This appears to be compliant with RFC 2131 Dynamic Host Configuration Protocol:

Under RFC 2131, the server should not return ordinary configuration options that were absent from the client’s Parameter Request List.

Now the problem: The ISC DHCP client dhclient used in the ISO installer system does not set option 119 explicitly in the client's Parameter Request List.
Option 119 is not listed in the ISO installer system's /etc/dhcp/dhclient.conf and it's not on the builtin Request List, as can be seen in a live network dump when DHCP happens, and finally in the log of the DHCP server.
(The Request List is already customized by Proxmox, as "Private" options 250 and 251 are added to /etc/dhcp/dhclient.conf, to make it all work completely with DHCP options only, without DNS TXT records.)

The ISO installer is now aborting with:

INFO: Retrieving default search domain.
INFO: Querying TXT record for 'proxmox-auto-installer.<MY-OWN-DOMAIN-NAME-BUT-NOT-SEARCH-DOMAIN>'
INFO: Fetching answer file via HTTP failed: Got empty response.
ERROR: Aborting: Could not find any answer file!

@ProxmoxVE staff: Could you please add option 119 (domain-search) to the /etc/dhcp/dhclient.conf in your official ISO?
Or am I just missing something else?

Thanks a lot!

 

[j.theisen]

Hi @MJ_UI

thanks for posting on the forum!

So if i understand correctly DHCP option 15 is set and applied correctly but your answer server uses a different domain and this would be supplied in the 119 option, correct?

Best regards
Jonas

 

[MJ_UI]

Hi @j.theisen,

thank you for your interest!

Yes, DHCP option 15 Domain Name is received, set and applied correctly by the DHCP client.
In /etc/resolv.conf, both options domain and search are set to the value of option 15 Domain Name.
I guess that's why the PVE ISO "automatic installation answer fetcher" is able to use a search-domain, but finally it's the wrong value, and therefore the DNS request for the TXT record fails.

I'm wondering how the instructions and examples in the official documentation for Automated Installation work, because the DHCP client apparently doesn't request option 119 from the DHCP server.
Did the author use a DHCP server that “simply” sends option 119 explicitly, without the client in the ISO requesting it?

Answer Fetched via HTTP​

To fetch the answer file via HTTP(S), the installer needs to know the URL. The URL may be provided via the following ways:

• ...
• via a DNS TXT record
  • The DNS TXT record needs to be located at proxmox-auto-installer.{search domain}, where {search domain} is the search domain provided by the DHCP server.

And we indeed must use the search-domain instead of the domain-name.