Installing and Administering Internet Services

292 Chapter7

Conﬁguring the Network Time Protocol (NTP)

Getting Started with NTP

Nonetheless, 85 milliseconds is not too bad for general NTP purposes.

You will generally see dispersion measurements somewhat less than the

ping round-trip times. The NTP daemon has an interesting watershed at

128 milliseconds, but this example server at 85 milliseconds is

comfortably below that. You can use the server at columbia.

/usr/sbin/ntpq -p ntp.ctr.columbia.edu

This time server at Columbia University has a variety of stratum-1,

stratum-2, and stratum-3 sources, which is good. It also has three

sources which are not responding right now (reach=0), and one with very

large delay, offset, and dispersion (tick.CS.UNLV.EDU). As before, this is

due to networking problems between client and server (New York to Las

Vegas, over 3000 km), not some fault with the NTP implementation at

either end. This time server at Columbia is currently synchronized to

NAVOBS1.MIT.EDU, but three others (marked with "+" in column one)

are attractive and could step in immediately if NAVOBS1 failed for any

reason.

Table 7-3 Evaluating Time Servers in Eastern United States

remote refid st t when poll reach delay offset disp

==============================================================================

+clepsydra.dec.c usno.pa-x.dec.c 2 u 927 1024 355 108.49 -18.215 3.63

otc1.psu.edu .WWV. 1 - 17d 1024 0 28.26 -25.362 16000.0

*NAVOBS1.MIT.EDU .USNO. 1 u 214 1024 377 38.48 -0.536 0.90

tick.CS.UNLV.ED tock.CS.UNLV.ED 3 u 721 1024 377 2113.97 1004.94 824.57

132.202.190.65 0.0.0.0 16 - - 1024 0 0.00 0.000 16000.0

unix.tamu.edu orac.brc.tamus. 3 u 636 1024 377 47.99 3.090 9.75

at-gw2-bin.appl 0.0.0.0 16 - - 1024 0 0.00 0.000 16000.0

-cunixd-ether.cc 192.5.41.209 2 u 172 1024 377 3.39 12.573 1.14

cunixd.cc.colum 0.0.0.0 16 u 285 64 0 0.00 0.000 16000.0

+cs.columbia.edu haven.umd.edu 2 u 906 1024 376 2.41 -5.552 15.12

+129.236.2.199 BITSY.MIT.EDU 2 u 423 1024 376 13.43 -14.707 22.60

cucise.cis.colu cs.columbia.edu 3 u 62 1024 377 5.84 -1.975 12.70