[ntp:questions] is USB inherently evil, or only if something else is on the bus?

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Wed Aug 8 22:50:48 UTC 2012


Rick Jones wrote:
> wondering about some of the previous discussion about USB
>  and how it is perhaps not "evil" but considered quite
>  sub-par for serving-up the PPS signal.
>
> Is that unsuitability inherent in USB, so it matters not
>  whether there is anything else on the USB, or is it more
>  a case of being "bad" generally only when other things
>  are on the same USB?  I'm still looking to go serial,
>  but was wondering.

Just, higher 7 less deterministic latency than a real serial port.


> If I happen to have say four servers in a location which
>  might loose its connectivity to the outside world I
>  probably don't want those servers to fall-back on
>  LOCAL(0) right?  Would configuring each to have the other
>  three as "peer" entities be the way to go?
>
> Pointers to the fine manual for any of the above would be welcome.

<http://www.eecis.udel.edu/~mills/ntp/html/orphan.html>
<http://www.eecis.udel.edu/~mills/ntp/html/miscopt.html#tos>
<http://support.ntp.org/bin/view/Support/OrphanMode>

When you have a group of computers on a LAN configured for
  orphan mode, and they lose contact with remote servers,
  the LAN client/servers will follow each other around.

 Then when the remote servers can be contacted again,
  the remote servers are selected.

e.g. I use something similar to this on all PCs / Devices
# ALL (Clients and/or Servers)
tos cohort 1 orphan 11
restrict default limited kod nomodify notrap
restrict 127.0.0.1
restrict source nomodify
keys "/etc/ntp.keys" # e.g. contains: 123 M YOUR_MD5_KEY
trustedkey 123
manycastserver  224.0.1.1
manycastclient  224.0.1.1 key 123 preempt
multicastclient 224.0.1.1 key 123 preempt
broadcastclient

.... and add Server, Pool, Peer and RefClock lines
     to your Primary Server (& Secondary if you have one).

e.g. peer clepsydra.dec.com iburst                    # Corp HP Western Research Laboratory, Palo Alto, CA
     server ntp-cup.external.hp.com iburst prefer     # Corp Cupertino CA (SF Bay area)
     server clock.via.net iburst                      # Local to Palo Alto, CA
     server clock.isc.org iburst                      # Local to Palo Alto, CA
     server 12.230.209.133 iburst                     # AS71 peer 7018
     server sl-crs1-ria-0-3-3-0.sprintlink.net iburst # AS71 peer 1239
     server tardy.usa.hp.com iburst                   # LAN
     pool 0.hp.pool.ntp.org iburst preempt            # HP doesn't actually appear to have a vendor pool?
     pool 0.dec.pool.ntp.org iburst preempt           # DEC doesn't actually appear to have a vendor pool?
     pool us.pool.ntp.org iburst preempt              # Regional pool in lieu of a vendor pool?


You might want to contact for advice:
 "timer at cup.hp.com" & "ntp-admin at wrl-mail.hpl.hp.com"

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