[ale] possibility of running an NTP server

[mike at trausch.us]

On 01/12/2012 01:12 AM, Ron Frazier wrote:
> The docs say you have to have a static IP and a permanent connection. 
> However, since the DynDNS service continually remaps the dynamic IP to a 
> fixed hostname, I thought it might work anyway. I think I can get 
> incoming queries if I port forward the router to the server. I'm not 
> familiar with bastion.

If you are going to run a public service, then yes, you need to have a
static IP (lots of clients will cache IP addresses so that they can
continue to work in the face of a DNS failure).

Even on a home network, you want to use a static IP, because DHCP only
allows you to to specify an IP address, not a hostname.  You can have
clients contact the NTP server directly, or you can configure them to do
one of the following:

 - On an IPv4 network, have clients listen on the network's broadcast
   address for time update announcements.

 - On an IPv4 network or an IPv6 network, have clients join the NTP
   multicast group and listen for time update announcements there.

IANA has reserved 224.0.1.1 on IPv4 and node address 0x0101 for IPv6 for
NTP.  IPv6 has different multicast scopes, but the node address stays
the same; for example, ff02::101 is the multicast address for "all NTP
servers on the local network segment" and ff08::101 is the multicast
address for "all NTP servers within an organization".

See http://en.wikipedia.org/wiki/Multicast_address for more base
information on multicast.

	--- Mike

-- 
A man who reasons deliberately, manages it better after studying Logic
than he could before, if he is sincere about it and has common sense.
                                   --- Carveth Read, “Logic”