[ntp:questions] negative estbdelay?

Dave Johnson djohnson at sw.starentnetworks.com
Thu Oct 25 17:45:56 UTC 2007


Danny Mayer writes:
> Dave Johnson wrote:
> > Danny Mayer writes:
> >> If you are not using autokey authentication then it doesn't do the
> >> autokey dance and as a result is unable to estimate the delay between
> >> the broadcast client and the broadcast server. You didn't include the
> >> client or server config file so it's hard to be sure.
> >>
> >> Danny
> > 
> > Even though, it should be doing a burst on startup to calculate some
> > sort of delay right?  I usually see 0.004 sec on all clients.
> > Shouldn't some sanity checking of the calcualted delay catch this?
> > 
> > 
> > No auth is on. This is an isolated, unconnected subnet.  Once host is
> > setup for broadcasting as a local reference, all other hosts are
> > clients of that one host.
> > 
> 
> Authentication is OFF. disable auth disables authentication. Therefore
> your client is totally passive and never sends a packet to the server
> and therefore it cannot estimate the delay.
> 
> Danny

It sends a burst when it first learns of a new broadcaster.  See
capture below.  It may not do this again as long as the broadcaster is
still sending, but it does it once at startup.

Somehow the system calcuated a negative broadcast delay.  That
shouldn't make any sense.  The broadcast delay should always be
positive right?

If this occurs what is the expected behaviour?  Throw away the peer and
try again once another broadcst is received?  Should it be marked
reject?  It seems the processing code is putting alot of trust in the
broadcast delay.  Should this be taken into account when selecting the
peer?




$ killall ntpd
$ ntpq -c lpeers
No association ID's returned

13:24:32.365788 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010375 ref EXTL at 3402321863.366989850 orig 0.000000000 rec -0.000000000 xmt -892645423.633241474 (DF) (ttl 64, id 0, len 76)

$ ntpq -c lpeers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 card8           .INIT.          16 u    -   64    0    0.000    0.000   0.001

13:24:47.366006 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010360 ref EXTL at 3402321879.366804718 orig 0.000000000 rec -0.000000000 xmt -892645408.633279383 (DF) (ttl 64, id 0, len 76)
13:25:03.367060 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010345 ref EXTL at 3402321895.366625756 orig 0.000000000 rec -0.000000000 xmt -892645392.632467150 (DF) (ttl 64, id 0, len 76)

$ ntpq -c lpeers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 card8           .EXTL.           1 u    2   64    1    0.077    0.371   0.001

13:25:19.787318 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 0 poll 6 prec -20 dist 0.000000 disp 0.000793 ref (unspec)@0.000000000 orig 0.000000000 rec -0.000000000 xmt -892645376.212694391 (DF) (ttl 64, id 0, len 76)
13:25:19.787423 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010360 ref EXTL at 3402321910.367581784 orig 3402321919.787305593 rec +0.000409111 xmt +0.000449330 (DF) (ttl 64, id 0, len 76)
13:25:20.366904 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010375 ref EXTL at 3402321910.367581784 orig 0.000000000 rec -0.000000000 xmt -892645375.632789134 (DF) (ttl 64, id 0, len 76)
13:25:21.787061 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 0 poll 6 prec -20 dist 0.000000 disp 0.000823 ref (unspec)@0.000000000 orig 3402321919.787754952 rec -0.000332315 xmt +1.999295771 (DF) (ttl 64, id 0, len 76)
13:25:21.787240 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010391 ref EXTL at 3402321910.367581784 orig 3402321921.787050724 rec +0.000427884 xmt +0.000471846 (DF) (ttl 64, id 0, len 76)
13:25:23.786813 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 0 poll 6 prec -20 dist 0.000000 disp 0.000854 ref (unspec)@0.000000000 orig 3402321921.787522554 rec -0.000282834 xmt +1.999278306 (DF) (ttl 64, id 0, len 76)
13:25:23.786956 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010421 ref EXTL at 3402321910.367581784 orig 3402321923.786800861 rec +0.000390036 xmt +0.000426804 (DF) (ttl 64, id 0, len 76)
13:25:25.787562 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 0 poll 6 prec -20 dist 0.000000 disp 0.000869 ref (unspec)@0.000000000 orig 3402321923.787227690 rec -0.000271731 xmt +2.000322920 (DF) (ttl 64, id 0, len 76)
13:25:25.787701 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010208 ref EXTL at 3402321925.367535859 orig 3402321925.787550568 rec +0.000396255 xmt +0.000433951 (DF) (ttl 64, id 0, len 76)

$ ntpq -c lpeers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*card8           .EXTL.           1 u    2   64    1    0.077    0.371   0.041

13:25:27.788290 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 2 poll 6 prec -20 dist 0.000106 disp 0.948120 ref 172.16.7.1 at 3402321925.787700772 orig 3402321925.787984549 rec -0.000283778 xmt +2.000297443 (DF) (ttl 64, id 0, len 76)
13:25:27.788453 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010238 ref EXTL at 3402321925.367535859 orig 3402321927.788281977 rec +0.000370007 xmt +0.000414823 (DF) (ttl 64, id 0, len 76)
13:25:29.788027 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 2 poll 6 prec -20 dist 0.000106 disp 0.948150 ref 172.16.7.1 at 3402321925.787700772 orig 3402321927.788696825 rec -0.000244078 xmt +1.999322175 (DF) (ttl 64, id 0, len 76)
13:25:29.788153 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010269 ref EXTL at 3402321925.367535859 orig 3402321929.788019001 rec +0.000344565 xmt +0.000375777 (DF) (ttl 64, id 0, len 76)
13:25:31.786769 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 2 poll 6 prec -20 dist 0.000106 disp 0.948165 ref 172.16.7.1 at 3402321925.787700772 orig 3402321929.788394749 rec -0.000241787 xmt +1.998362958 (DF) (ttl 64, id 0, len 76)
13:25:31.786906 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010299 ref EXTL at 3402321925.367535859 orig 3402321931.786757707 rec +0.000372182 xmt +0.000416864 (DF) (ttl 64, id 0, len 76)
13:25:33.786497 172.16.5.1.123 > 172.16.7.1.123:  [udp sum ok] v4 client strat 2 poll 6 prec -20 dist 0.000106 disp 0.948196 ref 172.16.7.1 at 3402321925.787700772 orig 3402321931.787174582 rec -0.000268849 xmt +1.999311208 (DF) (ttl 64, id 0, len 76)
13:25:33.786656 172.16.7.1.123 > 172.16.5.1.123:  [udp sum ok] v4 server strat 1 poll 6 prec -20 dist 0.000000 disp 0.010330 ref EXTL at 3402321925.367535859 orig 3402321933.786485791 rec +0.000355906 xmt +0.000394069 (DF) (ttl 64, id 0, len 76)



13:25:36.365777 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010375 ref EXTL at 3402321925.367535859 orig 0.000000000 rec -0.000000000 xmt -892645359.633967041 (DF) (ttl 64, id 0, len 76)
13:25:52.365645 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010375 ref EXTL at 3402321942.366216987 orig 0.000000000 rec -0.000000000 xmt -892645343.634139358 (DF) (ttl 64, id 0, len 76)
13:26:08.366496 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010391 ref EXTL at 3402321957.367191970 orig 0.000000000 rec -0.000000000 xmt -892645327.633341073 (DF) (ttl 64, id 0, len 76)
13:26:26.366027 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010406 ref EXTL at 3402321975.366708934 orig 0.000000000 rec -0.000000000 xmt -892645309.633792281 (DF) (ttl 64, id 0, len 76)
13:26:44.366631 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010421 ref EXTL at 3402321991.366525799 orig 0.000000000 rec -0.000000000 xmt -892645291.633217096 (DF) (ttl 64, id 0, len 76)
13:26:59.366564 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010406 ref EXTL at 3402322007.367342650 orig 0.000000000 rec -0.000000000 xmt -892645276.633299350 (DF) (ttl 64, id 0, len 76)
13:27:15.365424 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010406 ref EXTL at 3402322024.367021739 orig 0.000000000 rec -0.000000000 xmt -892645260.634476065 (DF) (ttl 64, id 0, len 76)
13:27:33.365983 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010421 ref EXTL at 3402322041.365706652 orig 0.000000000 rec -0.000000000 xmt -892645242.633927106 (DF) (ttl 64, id 0, len 76)
13:27:48.366942 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010391 ref EXTL at 3402322057.366526752 orig 0.000000000 rec -0.000000000 xmt -892645227.632979989 (DF) (ttl 64, id 0, len 76)
13:28:03.366907 172.16.7.1.123 > 172.16.63.255.123:  [udp sum ok] v4 bcast strat 1 poll 4 prec -20 dist 0.000000 disp 0.010375 ref EXTL at 3402322073.366334915 orig 0.000000000 rec -0.000000000 xmt -892645212.633028149 (DF) (ttl 64, id 0, len 76)

-- 
Dave Johnson
Starent Networks




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