isc dhcp server weird hostname option value

[Radoslav Pešek]

Thanks for your reply.

What I found si that you don't need any of those three options - option 
host-name caused problems, option dhcp.host-name didn't help but with 
option fqdn.hostname it seemed to work, but then I read man pages for 
dhcp-options and they say:

option fqdn.hostname --never set--;

          This  option should never be set, but it can be read back 
using the option and config-option operators in an expression, in which 
case it returns
          the first label in the fqdn.fqdn suboption - for example, if 
the value of fqdn.fqdn is "foo.example.com.", then fqdn.hostname will be 
"foo".

so I tried it without and everything seems to work (DDNS update 
included). So now I just have

          set mac_6 = suffix(concat("0", binary-to-ascii(16, 8, "", 
substring(hardware, 6, 1))), 2);
          ddns-hostname = concat("vm1", mac_6);

I don't know if it's correct so would appreciate any insight.

But I have another issue, which I initially thought is related to this, 
so would appreciate any halp there too - 
https://lists.isc.org/pipermail/dhcp-users/2017-June/020656.html.

Thanks again, Rado.


On 06/23/2017 04:23 PM, Bill Shirley wrote:
> I have a some devices that don't provide a hostname.  Dynamic DNS
> doesn't get updated without a hostname.  I use:
> # 
> ------------------------------------------------------------------------------
> class "NoName" {
>         match if not (
>                 exists server.ddns-hostname
>                 or exists fqdn.hostname
>                 or exists host-name
>         );
>
>         ddns-hostname = concat("NoName-", binary-to-ascii(16, 8, "", 
> substring(hardware, 4, 3)));
>         option dhcp.host-name = config-option server.ddns-hostname;
> #       option fqdn.hostname = config-option server.ddns-hostname;
> }
> # 
> ------------------------------------------------------------------------------
> to create a hostname for them.  It uses the last 3 bytes of the MAC 
> address
> as part of the host name.  Note: I'm using 'option dhcp.host-name' instead
> of 'option host-name'.  I really don't know if that matters.  You 
> might also
> try 'option fqdn.hostname'.
>
> You can even confine them to a pool:
>         pool {
>                 deny dynamic bootp clients;
>                 allow members of "NoName";
> .
> .
>         }
>
> HTH,
> Bill
>
> On 6/23/2017 7:28 AM, Radoslav Pešek wrote:
>>
>> Hi all,
>>
>> I sent this email few weeks ago (without being subscribed here), and 
>> didn't receive any reply, nor do I see it in lists archive. So I 
>> write once again after subscription, hope it will work now.
>>
>> ~~~~
>>
>> My isc dhcp server behaves strangely - it sends some clients dhcp 
>> hostname option value which I don't know where it is getting it from.
>>
>> It's on Debian 8.5, version 4.3.1. It's in failover mode.
>>
>> I'm using dynamic hostname generation for some clients based on last 
>> byte of their mac address:
>>
>> |set mac_6 = suffix(concat("0", binary-to-ascii(16, 8, "", 
>> substring(hardware, 6, 1))), 2); ddns-hostname = concat("vm1", 
>> mac_6); option host-name = config-option server.ddns-hostname; |
>>
>> So for example client with mac address ending 02 should get hostname 
>> vm102 - and it seems to work correctly - I added logging to my dhcp 
>> config and I see in log file both option host-name and config-option 
>> server.ddns-hostname set to vm102.
>>
>> I also see in dhcpd.leases
>>
>> |set mac_6 = "02"; client-hostname "vm102"; |
>>
>> But when I run tcpdump for this client, I see
>>
>> |Hostname Option 12, length 5: "vm121" |
>>
>> and at least once it changed to vm103.
>>
>> So where is it getting it from? What are the sources for this option 
>> when dhcp server sends DHCPOFFER or DHCPACK?
>>
>> It works after dhcp server restart, but then it starts again after a 
>> whlie.
>>
>> I tried to read isc-dhcp-server's source code but got bit lost as it 
>> was hard to follow.
>>
>> Thanks for any help.
>>
>> Rado.
>>
>>
>>
>>
>> _______________________________________________
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>> dhcp-users at lists.isc.org
>> https://lists.isc.org/mailman/listinfo/dhcp-users
>
>
>
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