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NTP issue

Anyone know what validity checks are done with NTP. I've got a hierarchy of a GPS receiver, core 6500s which have NTP server pointing to GPS, and across a WAN, remote 6500s which point to core site 6500s. These remote 6500s NTP sync OK to the core 6500s, but downstream 2950s, 7206s initially NTP sync to the remote 6500s, but then lose sync after a few minutes. Every possible NTP debug turned on gives no error messages other than: no select intersection (from NTP debug select) and nothing from NTP validity. Working w/TAC indicates a possible validity problem, but no NTP debug validity messages are output.


Have you tried the remote 2950s / 7206s pointing directly at the core 6509s (just as a test)? Also, try having one of the 7200s point just to one of the remote 6500s - that should help rule out validity issues. Also, if you have any authentication turned on, try turning it off and seeing if things get better....

Yes, thank you for replying. The remote 2950s/7206s pointing across the WAN directly to the far end core 6509s that have the VLAN that the GPS receiver resides in works fine (NTP syncs ok). It also works if pointing them to the far end 7513s which terminate the WAN links coming from the remote site. Only when I point the remote 2950s/7206s directly to the remote 6509s (both at the same site) does it fail. NTP syncs up initially, but then fails after anywhere from 3-8 minutes, but never with any NTP debug failure msg, other than "NTP: no select intersection", which I believe is just telling me it failed for some reason.

Also, to answer the rest of your reply, the 2950/7206s only have 1 NTP server statement (don't point them to both local 6500s). I've also got no NTP authentication turned on.