Re: [Fwd: Re: openntpd and ntpq]

[Arvid Grøtting <arvidg@netfonds.no>]

Peter Hessler <phessler@theapt.org> writes:

> My definition of worst case:  Loosing sync.

Hey!  That's my definition, too!

Well, one of them.  I like to look at what happens afterwards, too.

> xntpd refuses to reply to requests.  openntpd responds with system
> time.
>
> In this case openntpd behaves better than xntpd.  In my case, that
> was the main reason for switching.

Now, there are several possibilities here:

- openntpd runs as a client only, so responding doesn't apply.  (This
  is, after all, the default config.)

- an openntpd runs as the sole server of a network, or any number of
  openntpd servers that do, lose sync at the same time.  (This is a
  case where continuing to respond with system time is arguably a good
  thing.)

- one (set of) openntpd server(s) for a network loses sync, while
  another stays synced to an external source.[1]

Now, the first case isn't interesting.  What I find most interesting
about the second case is how to distinguish it from the third.  And
in the third case, I'm wondering:

How do clients (including other servers) know which servers are synced
to an external source and which ones aren't?

If they don't, what's keeping the network from drifting forever due to
a time-sync loop?


[1] example network:

ext1  ext2    ext3  ext4    ext5  ext6
  |    |        |    |        |    |
  -    -        -    -        |    |
  |    |        |    |        |    |
 openntp1------openntp2------openntp3
     |             |             |
     |             |             |
     a great number of sntp clients

ntpd.conf for openntp1:

server ext1
server ext2
server openntp2
server openntp3
listen on *

ditto for openntp2, openntp3.  openntp1 and 2 have lost external sync.

ntpd.conf for clients:

server openntp1
server openntp2
server openntp3

(The above is a normal and reasonably sensible NTP configuration, but
not a recommended SNTP configuration according to RFC 2030.  If it's
totally unsupported in the beating-head-against-wall sense, that's OK,
but then I think the manual should say so.)
-- 

Arvid

deceased equine flagellator from Norway, home of the trolls.