NTP Server IP Address ?

Question

Hi,
I have configured a Cisco 6509 core switch as a NTP master and allowed all my access switches to get their time synchronised with the core switch. Now, I want to configure the core switch to get itself synchronised with other public NTP server which would be reliable and genuine as our organisation is serving for healthcare. One of my friend has told me to use these IPs 128.249.1.1 or 128.2.136.71 as a NTP Server in the core switch. Should I use them?
Is Cisco recommends any Public IP for  NTP Server synchronisation? Please suggest.
Thanks & Regards,
Anil K. 

Answer 1

Disclaimer: I have no affiliation with Cisco in any way except where I work, we use some Cisco products (sw/hw). So take it however you will.
Personally, I would rather adopt the following approach suggested at http://www.pool.ntp.org/en/use.html, than hardcoding a couple of public NTP servers in a remote region:
"As pool.ntp.org will assign you timeservers from all over the world, time quality will not be ideal. You get a bit better result if you use the continental zones (For example europe, north-america, oceania or asia.pool.ntp.org), and even better time if you use the country zone (like ch.pool.ntp.org in Switzerland) - for all these zones, you can again use the 0, 1 or 2 prefixes, like 0.ch.pool.ntp.org. Note, however, that the country zone might not exist for your country, or might contain only one or two timeservers. If you know timeservers that are really close to you (measured by network distance, with traceroute or ping), time probably will be even better. "
Of course, if time sync is REALLY that important, one might consider buying/installing commercial GPS-based NTP appliances. That's not what you're looking for, obviously.