[Dnsmasq-discuss] dhcp-host problem/questrions

[Gene Czarcinski]

On 12/19/2012 05:01 PM, Gene Czarcinski wrote:
> On 12/19/2012 11:48 AM, Simon Kelley wrote:
>> On 19/12/12 16:21, Gene Czarcinski wrote:
>>> On 12/19/2012 08:20 AM, Simon Kelley wrote:
>>> Give what you say above about DHCPv6, what needs to be specified by
>>> dhclient so that it can get nailed-address if one is available?  If it
>>> just asks for all of the addresses, how will it know the correct one to
>>> use?
>>>
>> It's the opposite: it shouldn't ask for an address at all, then dnsmasq
>> will offer it the nailed-down address. Deleting the client's saved state
>> should do this.
>>
> Maybe, maybe not.
>
> I ran a little test running wireshark on the system with the dnsmasq 
> dhcp server.  One system was the one with the nailed IP addresses. The 
> second had "regular" dhcp addresses.  I did not erase the lease files.
>
> 1. With the nailed system, there is a series of four DHCPv6 packets: 
> from nailed to server Confirm with nameand the IPv6 address; from 
> server to nailed Reply saying Confirm failed;  from nailed to server 
> Solicit with the name; from server to nailed Advertise with FQDN and 
> IPv6 address.
>
> A little later, there are two more DHCPv6 packets: from nailed to 
> server Request asking for a list of info; and from server to nailed 
> Reply with the answers to the info request.
>
> 2. With the "regular" client there are only two packets: from client 
> to server Request with name and IPv6 address (similar to the one 
> above) followed by from server to client Reply saying "All addresses 
> still on link"
>
> I have the trace files and I can send them but I do not want to put 
> them on the list.  They are not that bit but nevertheless.
>
> What the above says to me is that things were/are working correctly 
> and when the nailed system asked for the confirm, it was denied. But, 
> what does dnsmasq do if it gets another IPv6 address even if the host 
> name is the same?
>
> I believe I can cause the condition where a different IPv6 was 
> assigned.  In addition, I think I can fake things to recreate the 
> condition just before I discover what had happened.
>
> I may be wrong (it would not be the first time) but dnsmasq may not be 
> clean.  No matter what IPv6 address it is given, it should fail the 
> confirm because of the name match.  I suspect that if I used the 
> DHCPv6.client-id, everything would work.
>
> Oops.  I realized I had to run a third test.  Test #2 was with an F18 
> client so I reran the test with a F17 client.  Two packets: Confirm 
> followed by a Reply saying "All addresses still on link. Something in 
> F18 changed things to a Request rather than a Confirm.
>
I have been doing some additional testing and the fact that I ran a 
version of NetworkManager which did not support dynamic DNS cause new 
IPv6 addresses.  It was also interesting that dhclient will nicely 
create a new/different client-id every time it is started and the is no 
lease file ... a new one every time and dnsmasq naturally gives it a new 
IPv5 address.

If you then install the NetworkManager supporting dynamic DNS (which 
also changes the location of dhclient's lease files) and restart you do 
get the yet another client ID but you do not get the nailed address.

When I rebooted back to F17, I get the nailed address because the F17 
client-id/IPv6-address was still in dnsmasq's lease file and dhclient 
was still using the old client-id in the lease file.

I believe there might be an "undesirable feature" in dnsmasq which does 
not always honor/override with the dhcp-host= setting.

I have wireshark captures of all the the tests as well as the 
dnsmasq-leases file if you would like to see them.

Gene