[OLPC Networking] Re: NTP core dump

[Marc Blanchet]

Le 06-04-18 à 15:46, Jim Gettys a écrit :

> On Tue, 2006-04-18 at 01:33 -0700, Hal Murray wrote:
>>
>> I think the right way for most users to configure NTP is to  
>> specify the
>> servers via DHCP.  The DHCP RFCs have allocated a slot for NTP,  
>> but I don't
>> think anybody does this yet.

I used to do it in my dhclient.conf file on my freebsd.

>> Or at least not much.  Maybe some distribution
>> rewrites /etc/ntp.conf, the normal parameter/configuration file  
>> for ntpd.
>
> No, I suspect that mDNS is a better way these days.
>
> DHCP doesn't even exist in the conventional sense in IPv6. (though  
> there
> are some things like it).

DHCPv6 exist the "same" way as DHCP (v4). It does more. However, for  
interface autoconfiguration, dhcpv6 is not required. another method  
exist.

>
>
>>
>> There is a chicken/egg mess in here.  Most ISPs don't run NTP  
>> servers for
>> their customers so they don't have any IP Addresses to plug into  
>> their DHCP
>> answers (or web pages) so that path isn't well supported.
>
> We're talking to Vint at Google around IPv6 deployment; would be good
> maybe to use a set of servers they might provide world wide, for  
> the top
> stratum.

A colleague ported ntp to ipv6 a while ago (~2000). We then had the  
first ipv6 stratum-1 ntp server. Since then, I remember some have  
deployed it, but I don't have the details in hand. So I can confirm  
it is doable to run an ipv6-ntp server.

>
>>
>> For running your own stratum 1 server, the best deal I know of  
>> today is the
>> Garmin GPS-18 LVC.  You can get one for under $100.  Some assembly  
>> required.
>> The typical hack is to power it from USB.  (Beware, there are two  
>> other
>> versions of the GPS-18.  They don't support the PPS signal that  
>> you need for
>> good timekeeping.)
>
> Interesting; might be cheap enough to put one in each school or so.

remember: GPS signal might not be great (i.e. does not work) inside.  
so need to put the antenna kinda outside or very very close to a window.

>>
>> The other approach is for each base station to run a NTP server  
>> and for the
>> nodes of the local mesh to all use it as their (primary) server.   
>> Are you
>> going to use DHCP?  Does the answer come from the base station?   
>> If so, that
>> seems like a reasonable fit, assuming somebody can teach NTP to  
>> use DHCP.
>
> Probably advertise the base station NTP server via mDNS.

make sense to me.

>   See
> www.avahi.org.
>
>>
>> That brings up the next question.  What sort of connectivity are  
>> you going to
>> have from a base station (if that is even a reasonable concept) to  
>> the rest
>> of the world?  What's the ratio of end/mesh nodes to base  
>> stations?  Is it
>> reasonable to manually configure base stations?  .
>
> Depends.
>
> Anything from a wet string, or IP over avian carriers,

be careful on avian flu... ;-)

Marc.