Re: [dhcwg] New Version Notification for draft-wing-dhc-dns-reconfigure-01.txt

["Prashanth Patil (praspati)" <[e-mail]>]

Hi Ted,

On 02/07/13 12:28 AM, "Ted Lemon" <[e-mail]> wrote:

>(ad hat off)
>
>On Jul 1, 2013, at 9:32 AM, Prashanth Patil (praspati)
><[e-mail]> wrote:
>> Yes, this was one of the suggestions made earlier. Notification from
>>relay
>> then becomes generic and not specific to DNS. The server decides
>>whatever
>> actions need to be done, such as reconfiguring DNS server lists.
>
>I'm sorry, but you did not answer my question.   The question was this:
>
>>> Why don't you just configure the DHCP server to return DNS servers in a
>>> different order for different links?   Links are identified by relay
>>> agent, so this gets you the precise behavior you want, but with a
>>> centralized configuration file rather than with per-relay
>>>configuration.
>
>That is, I am not suggesting this as an alternative.   I am asking you
>why you don't consider this to be a better alternative.
>
>The reason I ask is that what you are proposing is extremely harmful.
>You are requiring new special protocol extension with new special-case
>code to be added to the DHCP server to handle this use case, and you are
>requiring that relay agents throughout the network be individually
>configured to specify behavior on the DHCP server, which is a maintenance
>nightmare.
>
>So if you want to do something this harmful, you should have a good
>explanation for why it's better than the alternative.

A static DNS order for different links introduces sub-optimal behavior
during transitions unless the servers are re-prioritized or until the host
stack re-initializes.
The draft proposes that a relay indicate dynamic transitions of the host
to the server which the server cannot learn otherwise or at best until the
next request eg: Dual-Stack-only to IPv6-only transition. With some
generalization to the proposal, a DHCP server could provide desired config
updates in a more responsive manner when the relay notifies host mode
changes without specifying behavior eg "Host changed from mode X to mode
Y".

-Prashanth



>