[ntp:questions] Re: asyncronous path between "time client" and ntp server

Bob Beers bob.beers at gmail.com
Mon Oct 10 19:37:07 UTC 2005


Thanks for your reply,

BTW, I really meant asymmetrical, not asynchronous, but the former
would likely imply the latter.

>My ntp server gets time info from pool.ntp servers and is looking ~ok to
> me:
> >
> ># ntpq -p
> >remote refid st t when poll reach delay offset jitter
>
> >==============================================================================
> >*gabe.kjsl.com <http://gabe.kjsl.com> <http://gabe.kjsl.com> 208.184.49.9<http://208.184.49.9><
> http://208.184.49.9> 2 u
> >935 1024 377 181.340 5.539 0.125
> >+ns3.dns.pciwest 132.163.4.103 <http://132.163.4.103> <
> http://132.163.4.103> 2 u 1022 1024 377
> >186.187 3.159 1.155
> >rrcs-24-172-8-1 .STEP. 16 u - 1024 0 0.000 0.000 4000.00
> >
> >
> >
> >
> That does not look "fine" to me. You have only three servers
> configured which is ok until something happens to one of them, which it
> has. rrcs-24-172-8-1 is not responding! So you are down to two
> servers, one of which has a round trip delay of 186 milliseconds and the
> other has a delay of only 180 milliseconds.



yes, I only said ~ok. The unit is in Brazil and had been configured
with us.pool.ntp.org <http://us.pool.ntp.org> servers. my bad.

Do try to find some servers a little closer to you in net space. 180
> milliseconds of round trip delay means that the potential error in the
> time you receive is 90 milliseconds. Hopefully the actual error is less
> than that but you are leaving yourself wide open. Try to find at least
> four of them. Unless your internet connection is a 1200 baud dial-up
> modem, you should be able to find servers with delays under 30
> milliseconds.
>
> ISTR that the pool.ntp servers can be specified by region which might
> help you find servers a little closer to home.



I will change to br.ntp.pool.org <http://br.ntp.pool.org>, but how do I
specify 4 unique
servers in br.pool? 0., 1., and 2. seem to work, but 3. does not resolve.
How would I specify all (6) br servers?

>When I traceroute between my client and server, I do not see a common
> public
> >NAT IP address, so I strongly suspect an asynchronous path between the
> two.
> >
> >
> >
> Post your ntp.conf file.
>
>
How does this look?

h:/tmp# cat /etc/ntp.conf
restrict default ignore
restrict 127.0.0.1 <http://127.0.0.1>

server 0.br.pool.ntp.org <http://0.br.pool.ntp.org> iburst
restrict 0.br.pool.ntp.org <http://0.br.pool.ntp.org> nomodify notrap nopeer
noquery
server 1.br.pool.ntp.org <http://1.br.pool.ntp.org> iburst
restrict 1.br.pool.ntp.org <http://1.br.pool.ntp.org> nomodify notrap nopeer
noquery
server 2.br.pool.ntp.org <http://2.br.pool.ntp.org> iburst
restrict 2.br.pool.ntp.org <http://2.br.pool.ntp.org> nomodify notrap nopeer
noquery
server pool.ntp.org <http://pool.ntp.org> iburst
restrict pool.ntp.org <http://pool.ntp.org> nomodify notrap nopeer noquery


fudge 127.127.1.0 <http://127.127.1.0> stratum 10
server 127.127.1.0 <http://127.127.1.0>
logfile /var/log/ntp.log


And with this ntp.conf and running for ~10 minutes:
h:/tmp# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
+200.141.215.162 200.19.74.21 <http://200.19.74.21> 3 u 38 64 177 1.549
21.611 0.796
titan.cais.rnp. 99.117.135.255 <http://99.117.135.255> 2 u 173 256 17
534.701 -273.25 25.107
ima.cipsga.org <http://ima.cipsga.org>. .STEP. 16 u - 1024 0 0.000 0.000
4000.00
*time.uswo.net <http://time.uswo.net> 128.10.252.6 <http://128.10.252.6> 2 u
43 64 177 150.938 26.492 0.902
LOCAL(0) 73.78.73.84 <http://73.78.73.84> 5 l 55 64 177 0.000 0.000 0.001

running for ~15 minutes:

h:/tmp# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
+200.141.215.162 200.19.74.21 <http://200.19.74.21> 3 u 26 64 377 1.039
3.905 15.877
titan.cais.rnp. 104.101.79.255 <http://104.101.79.255> 2 u 106 1024 77
534.701 -273.25 42.700
ima.cipsga.org <http://ima.cipsga.org>. .STEP. 16 u - 1024 0 0.000 0.000
4000.00
*time.uswo.net <http://time.uswo.net> 130.126.24.44 <http://130.126.24.44> 3
u 32 64 377 150.767 -1.882 25.244
LOCAL(0) 73.78.73.84 <http://73.78.73.84> 5 l 50 64 377 0.000 0.000 0.001


-Bob



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