TamTam roundup.

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Sun May 20 19:51:36 EDT 2007


[your mail violates RFC2822 for the In-Reply-To header which breaks
threading display, probably a mailer bug]

On 21.05.2007 00:52, Hal Murray wrote:
>> If any magic name has to be used, try pool.ntp.org. Maybe not nice,
>> but better than a newly invented name.
> If anybody isn't already familiar with the UWisc/Netgear story, here's the 
> URL:
>   http://www.cs.wisc.edu/~plonka/netgear-sntp/
>   Flawed Routers Flood University of Wisconsin Internet Time Server
> I call it required reading for anybody interested in networking.
> Unless you have permission from the owner, it's a really really bad idea to 
> wire a name or IP address into any system and them ship zillions of those 
> boxes.

That's why I suggested pool.ntp.org. It exists exactly for that purpose.

> Even if you do have permission, you should probably use a name or address of 
> your own in order to avoid an external dependency on some infrastructure that 
> you don't have any control over.

Valid point.

>> There is a standard for time serving via DHCP.
> That's not time serving itself.  That's distributing the IP Address of a time 
> server.

It should have been clear from the context that I meant exactly that.

> ntpd doesn't support getting the server address directly via DHCP.

But as you show below, it can be fed with the server address obtained
via DHCP.

> gentoo has a NTP wiki page that includes using DHCP
>   http://gentoo-wiki.com/HOWTO_NTP
> Basically, they are rewriting ntp.conf on the fly
> None of the systems I've worked with have done that.

This means the systems you've worked with have room for improvement.

> ntpd has a couple of multicast/broadcast modes.  They may be appropriate.
> I've never worked with them.

I gave a few pointers in the mail you replied to. They even deal with
network load of such multicast/broadcast approaches. Maybe I should be
more verbose next time.

> How are the XOs going to find their backup server?

You can provide a list of NTP servers via DHCP. Quoting from RFC 2132:
"Network Time Protocol Servers Option
 This option specifies a list of IP addresses indicating NTP
 servers available to the client.  Servers SHOULD be listed in order
 of preference."

In a multicast/manycast/broadcast configuration, having a second NTP
server should suffice.


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