Killing time


mills@dcn6.arpa
14-Feb-86 07:37:08-UT


Folks,

It has been about six months since the series of experiments on Internet clock
synchronization reported in RFC-756 et seq, so I thought you might enjoy a
capsule description of a recent repeat of some of them. Some fascinating (at
least to a slightly fractured bunch of us) phenomena seem to be oozing from
the data which might have to wait detailed archeological excavation; however,
some tidbits sticking from the murk are relishable in this note.

The experiments involved sending datagrams between intrepid fuzzball DCN6 to
each and every one of the 2135 hosts listed in the latest NIC file HOSTS.TXT.
Three protocols were used, one with ICMP Timestamp messages, a second with the
TIME protocol based on UDP and the third with the new NTP protocol, also based
on UDP. Four messages in each of the three protocols were sent to each host
and each reply recorded and processed to produce an offset estimate
representing the difference, in milliseconds, between the clock at the target
machine and the clock at DCN6. The DCN6 clock is synchronized using local-net
protocols to within a few milliseconds of a WWVB radio clock, so for the
purposes here its clock can be considered a reference standard.

Before describinb the results of the experiments themselves, it might be of
interest (says he coyly) to reflect on the health of the Internet innards in
which these datagrams were digested. The following menus summarize the
metabolic products of the three-course meal, which took over 24 hours and
25000 datagrams to swallow. ICMP Timestamp, UDP/NTP and UDP/TIME volleys were
sent to each host one after the other, so that accurate comparisons could be
made between them. If at least one valid reply was received for a protocol,
the volley was recorded as successful; while, if not, the last received error
message (if available) or "no response" was recorded.

2135 ICMP timestamp request sent
722 ICMP timestamp valid reply
72 ICMP invalid timestamp reply (marked unknown or invalid time)
170 ICMP host unreachable
111 ICMP net unreachable
11 ICMP time exceeded (probably a loop)
4 Local host down
1215 No response

2135 UDP/TIME request sent
229 UDP/TIME valid reply
4 UDP invalid packet format (echo host swapped ports)
161 ICMP host unreachable
114 ICMP net unreachable
433 ICMP port unreachable (TIME not implemented)
42 ICMP protocol unreachable (UDP not implemented)
11 ICMP time exceeded (probably a loop)
4 Local host down
1137 No response

2135 UDP/NTP request sent
24 UDP/NTP valid reply
178 ICMP host unreachable
115 ICMP net unreachable
521 ICMP port unreachable (NTP not implemented)
42 ICMP protocol unreachable (UDP not implemented)
10 ICMP time exceeded (probably a loop)
4 Local host down
1241 No response

The most disturbing feature of the above is the astonishing incidence of black
holes (no response). The scarred old warriors among us hate these things
passionately, since they often result in long hours of snoop when something
breaks. A little prying revealed that some number of these were the result of
dropping an otherwise valid reply due to IP or UDP format or checksum problems
at the sender. These provoke more deja vu than surprise, since similar bugs
have been reported and re-reported in famous implementations for years. One
inspired felon even returned all ICMP error messages with a runt ICMP header
too short by four octets. I did manage to explain all the ICMP-time-exceeded
and local-host-down complaints (except one) as originating in our swamp.

Turning now to the valid sample population, it is apparent that the discipline
of the truth-timetellers is somewhat better than last time - only one host was
found nearly exactly one day off (sic) and two were found with blatently
nonsense ICMP times. Taking just the 139 hosts (298 total replies) with
samples from two or more of the three protocols, for example, reveals the
following summary:

Host Address ICMP NTP UDP Notes
-------------------------------------------------------------------------
DCN6.ARPA [128.4.0.6] 0 -48 612
DCN-WWVB.ARPA [128.4.0.15] 1 -466 WWVB echo
ETAM-ECHO.ARP [4.0.0.62] -3 105 -199 IP echo
ISI-ECHO.ARPA [10.1.254.27] -6 26 -22 IP echo
DCN5.ARPA [128.4.0.5] 7 -20 -168
DCN1.ARPA [128.4.0.1] -8 -35 -162
DCN8.ARPA [128.4.0.8] -21 -29 -514
GW.UMICH.EDU [35.1.1.1] -48 -7 -219
TANUM-ECHO.AR [4.0.0.64] -48 3528 -3718 IP echo
WWV.UMICH.EDU [35.1.1.17] -58 -627 WWV echo
FORD1.ARPA [128.5.0.1] 62 -6 -16
DCN-WWV.ARPA [128.4.0.14] -75 -11 WWV echo
UMD1.UMD.EDU [128.8.0.1] 100 55 360
SATNET-ECHO.A [4.0.0.40] 277 180 703 IP echo
GOONHILLY-ECH [4.0.0.63] 294 141 -3021 IP echo
XYZZY.UMICH.E [35.1.1.3] -321 -315 -578
RAISTING-ECHO [4.0.0.77] 479 -12 -4821 IP echo
ORNL-MSR.ARPA [26.3.0.41] 497 -915
STC.ARPA [128.16.9.9] -665 3 -2858 IP echo
SALLY.UTEXAS. [10.2.0.62] -1478 -2542
AMES.ARPA [26.0.0.16] -1490 -1294 -1408
IPTO-FAX.ARPA [192.5.18.51] -1975 -2119 -1882
IPTO-ECHO.ARP [192.5.18.52] -2000 -627 UDP echo
ORION.ARPA [192.12.49.2] 2074 914 1314
USC-OBERON.AR [10.0.0.121] 2484 932
ROCHESTER.ARP [10.0.0.15] 3633 2500
SCORPIO.THINK [192.5.104.195] 5196 4395
C.CS.UIUC.EDU [192.5.69.3] 5242 4568
MIT-MULTICS.A [10.0.0.6] -6606 -7651
BRAND.USC.EDU [192.5.10.61] 7887 6792
DWORKIN.USC.E [192.5.10.64] 8516 7306
GRANITE.ARPA [128.45.0.101] -10023 -10790
A.CS.UIUC.EDU [10.3.0.37] -10373 -10988
ICSC.UCI.EDU [192.5.19.3] 10414 9654
ICSD.UCI.EDU [192.5.19.4] 11184 12025
NETWOLF.UMD.E [128.8.1.13] -11498 -12204
COLUMBIA.EDU [10.3.0.89] -11868 -14486
NYU-CSD2.ARPA [192.5.15.132] -14138 -14036
DOCKMASTER.AR [26.0.0.57] -15842 -17585
DCN9.ARPA [128.4.0.9] -16860 -16866 -17677
NOSC-GUPPY.AR [128.49.0.3] -17211 -17908
TRANTOR.UMD.E [128.8.0.14] 17922 17938 16846
HI-MULTICS.AR [10.1.0.94] 21274 20242
TB.CC.CMU.EDU [128.2.253.34] 22848 24304
SU-SAFE.ARPA [36.44.0.193] 25114 25908
PATCH.ARPA [26.6.0.2] -26211 -27396
BBNCC5.ARPA [128.89.0.88] -27836 -32280
ATRP.MIT.EDU [18.85.0.3] 30453 29554
NPRDC-PACIFIC [192.5.65.2] -31432 -32233
TF.CC.CMU.EDU [128.2.253.38] 33023 34611
GARFIELD.COLU [128.59.16.2] -36358 -35630
TC.CC.CMU.EDU [128.2.253.35] 39542 40695
USGS2-MULTICS [26.0.0.69] -45500 -46397
B.CS.UIUC.EDU [192.5.69.2] -51185 -52065
CU-ARPA.CS.CO [10.3.0.96] -54810 -55610
ICSE.UCI.EDU [192.5.19.5] -58193 -59623
USC-ISIC.ARPA [10.0.0.52] -59430 -59212
TD.CC.CMU.EDU [128.2.253.36] 59699 60560
NPRDC.ARPA [26.3.0.3] 67029 64915
UCI.EDU [192.5.19.1] -70709 -71224
CIP3.UCI.EDU [192.5.19.8] -74679 -76161
SU-AIMVAX.ARP [36.45.0.193] 84666 83903
NYU-ACF5.ARPA [192.5.15.13] -88445 -91559
MERLIN.PURDUE [192.5.48.3] 88691 87860
MITRE-BEDFORD [26.3.0.66] 90742 90366
NS2.CS.UCL.AC [128.16.5.2] 97395 96411
MEDIA-LAB.ARP [18.85.0.2] 100189 99256
TE.CC.CMU.EDU [128.2.253.37] 107915 108221
CIP4.UCI.EDU [192.5.19.11] -109144 -109610
BLAYS.PURDUE. [128.10.2.7] 123395 119781
FAS.RI.CMU.ED [128.2.254.138] -129306 -130533
CAD.CS.CMU.ED [128.2.254.133] -134145 -135394
THEORY.CS.CMU [128.2.254.182] -137348 -138211
GANDALF.CS.CM [128.2.254.140] -139830 -140677
CIVE.RI.CMU.E [128.2.254.177] -139857 -140732
H.CS.CMU.EDU [128.2.254.156] -140138 -141135
SAM.CS.CMU.ED [128.2.254.181] -140886 -141504
K.CS.CMU.EDU [128.2.254.137] -143272 -144436
SENSOR.RI.CMU [128.2.254.147] -144797 -145883
SPEECH1.CS.CM [128.2.254.145] -145322 -146576
ME.RI.CMU.EDU [128.2.254.142] -145774 -146565
CIP.UCI.EDU [192.5.19.6] -146244 -146019
NYU-ACF2.ARPA [192.5.15.9] 146843 145399
C.CS.CMU.EDU [10.3.0.14] 149915 150837
IUS1.CS.CMU.E [128.2.254.128] -150642 -151298
VI.RI.CMU.EDU [128.2.254.158] -150781 -151567
SPICE.CS.CMU. [128.2.254.139] -151411 -152188
ARM.RI.CMU.ED [128.2.254.151] -152310 -153136
MAPS.CS.CMU.E [128.2.254.184] -152825 -153692
ISL1.RI.CMU.E [128.2.254.143] -154190 -155976
ML.RI.CMU.EDU [128.2.254.178] -155618 -156754
IUS2.CS.CMU.E [128.2.254.176] -157583 -158408
A.SEI.CMU.EDU [128.2.254.131] -158382 -159449
SU-MOJAVE.ARP [36.10.0.14] -162822 -163537
SPEECH2.CS.CM [128.2.254.179] -165127 -166118
SU-SONOMA.ARP [36.20.0.99] -167543 -167882
PT.CS.CMU.EDU [128.2.254.155] -198025 -198966
MITRE.ARPA [26.0.0.17] 201594 200484
NYU.ARPA [26.0.0.58] 207805 207160
SU-ARGUS.ARPA [36.9.0.10] -216438 -216367
ROVER.RI.CMU. [128.2.254.157] -218641 -219583
MIT-HERA.ARPA [18.58.0.3] -226707 -227641
MIT-APOLLO.AR [18.58.0.10] -233509 -234152
SU-HELENS.ARP [36.2.0.5] 241465 240527
MIT-DEMETER.A [18.58.0.4] -265113 -266357
MIT-APHRODITE [18.58.0.12] -265862 -266957
MIT-CASTOR.AR [18.71.0.5] -267411 -268406
MIT-ATLAS.ARP [18.58.0.15] -268763 -269762
MIT-HELEN.ARP [18.71.0.11] -269498 -270900
MIT-HECTOR.AR [18.71.0.13] -275008 -275890
MIT-THESEUS.A [18.71.0.2] -280386 -281468
MIT-ARTEMIS.A [18.58.0.11] -282770 -283816
MIT-ORPHEUS.A [18.71.0.4] -286828 -287853
MIT-MENELAUS. [18.71.0.17] -294194 -294229
SU-FUJI.ARPA [36.2.0.9] 295277 294896
MIT-JASON.ARP [18.71.0.7] -296300 -297382
MICRO.UDEL.ED [192.5.39.4] 297334 296792
MIT-PRIAM.ARP [18.71.0.14] -300702 -301975
MIT-PARIS.ARP [18.71.0.12] -301652 -302932
ATHENA.MIT.ED [18.58.0.1] -301792 -303244
MIT-ODYSSEUS. [18.71.0.15] -303007 -304354
MIT-ZEUS.ARPA [18.58.0.2] -305836 -307120
MIT-HERACLES. [18.71.0.3] -309782 -310816
RADC-MULTICS. [26.0.0.18] -313852 -314576
MIT-POSEIDON. [18.58.0.6] -321949 -322546
DEWEY.UDEL.ED [192.5.39.2] 322621 322913
SU-COYOTE.ARP [36.18.0.215] -322956 -323303
BBNG.ARPA [192.1.2.67] -331109 -331111
UW-KRAKATOA.A [192.5.8.45] -333876 -334815
MIT-AGAMEMNON [18.71.0.16] -341461 -342518
NYU-ACF4.ARPA [192.5.15.133] -419460 -420123
CIP2.UCI.EDU [192.5.19.7] -435654 -435619
SU-LINDY.ARPA [36.9.0.11] -449513 -448490
VLSI.CS.CMU.E [128.2.254.129] -480627 -481678
NYU-CSD1.ARPA [192.5.15.131] -715648 -717005
SU-PESCADERO. [36.8.0.8] -751799 -751814
AMES-ATLAS.AR [192.12.49.50] -792499 -793442
S1-A.ARPA [26.1.0.95] 114428000 -773226
SU-AI.ARPA [10.0.0.11] 115126000 -76368

Notes
WWVB echo Synchronized to WWVB radio; swaps addresses and ports
WWV echo Synchronized to WWV radio; swaps addresses and ports
GOES echo Synchronized to GOES satellite; swaps addresses and ports
UDP echo Swaps addresses and ports
IP echo Swaps addresses

If anybody is interested in further details, raw data or pretty pics to light
up your Sun, please tinkle me directly.

Dave
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