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NTP servers

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Last Modified: 2012-05-06
where's the best place to find reliable NTP servers to use? I am on the east coast for what its worth

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if I configure an external NTP server on a router or firewall, do I need to open up udp 123?  if its a stateful firewall, shouldn't it allow the traffic back in?
no you shouldnt have to unless you are specifically blocking the NTP port (udp 123)
you are establishing the connection from the device so you should be fine.


ok, i added those ntp servers you had and this is what I have. is this normal? Is it synched?
Central_FL_Gas#sh ntp stat
Clock is unsynchronized, stratum 16, no reference clock
nominal freq is 250.0000 Hz, actual freq is 249.9984 Hz, precision is 2**18
reference time is CD5AD3D9.60F6E8AE (22:42:33.378 UTC Thu Mar 5 2009)
clock offset is 3.8501 msec, root delay is 152.95 msec
root dispersion is 7.86 msec, peer dispersion is 0.46 msec
Central_FL_Gas#sh ntp assoc
      address         ref clock     st  when  poll reach  delay  offset    disp
 ~          16     -    64    0     0.0    0.00  16000.
 ~          16     -    64    0     0.0    0.00  16000.
 ~          16     -    64    0     0.0    0.00  16000.
 ~          16     -    64    0     0.0    0.00  16000.
 * master (synced), # master (unsynced), + selected, - candidate, ~ configured

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no thats not right at all, thats not connecting to any of the NTP servers...below is what it should look like
is this an edge router or located behind other devices?

show ntp ass
      address         ref clock     st  when  poll reach  delay  offset    disp
+~     .ACTS.            1   697  1024  377     3.0    6.16     2.8
+~      .CDMA.            1   755  1024  377     8.1   -0.07     0.5
*~   .CDMA.            1   710  1024  377     7.7    3.23     0.7
 ~      .ACTS.            1   110  1024  377   111.7   46.91    13.6
 * master (synced), # master (unsynced), + selected, - candidate, ~ configured

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its a remote site, which connects to us via MPLS. Its internet traffic goes out our (headquarters) firewall and router
can you ping the address from the router?


I do have a router (facing the internet) that does have access to an external NTP server. Should I point my routers to that?
yeh what you can do is setup the other router to get the time and then use that as a server for the back one...pretty much what i do so the wan router is a stratum 2 ntp server

just add the ntp master 1 command to the wan router...the 1 is how many stratums away from 0 so assuming that router connections to a stratum 0 router your wan router is in stratum 1

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