Subject: Re: [dhcwg] IP address vs. FQDN discussion

From: Danny Mayer <[email-masked]>
Date: Sat, 01 Dec 2012 09:54:39 -0500

On 11/30/2012 12:25 PM, Danny Mayer wrote:
> On 11/30/2012 9:08 AM, Ted Lemon wrote:
>> On Nov 29, 2012, at 10:14 PM, Danny Mayer <[email-masked]> wrote:
>>> NTP will use all addresses it can get up to 10 if you use the pool
>>> option but it can only do that with FQDN addresses.
>>
>> So you can't give it a list of ten IP addresses, but you can give it
> an FQDN? If true, this is simply an implementation bug, and requires no
> protocol action to correct.
> 
> 
> No that's not true and an assumption on your part. The pool option is an
> implementation design and not a protocol issue. If you use the pool DNS
> servers (pool.ntp.org) you will get a different list of addresses every
> time you ask. Failure of one address will cause it to go out and find
> new addresses.
> 

Here's additional detail about the pool option:

The answers returned by the pool servers have a short TTL.  They get
rotated quickly.  ntpd will use what it gets, then try again,
occasionally, until it gets enough unique working addresses.  Addresses
that don't respond get dropped.  During startup, it may add more than it
needs if some of the ones added recently haven't responded yet.  The
extras will get dropped.

Danny