From mbrett@rgs0.london.waii.com Sat Oct 24 18:14:15 PDT 1998 Article: 7373 of comp.protocols.time.ntp From: Marc Brett Newsgroups: comp.protocols.time.ntp Subject: Re: Why NTP? Date: 21 Oct 1998 09:04:21 GMT Organization: Western Geophysical, Div. of Western Atlas Int'l, Houston, TX Lines: 73 Distribution: inet Message-ID: <70k82l$i8m$1@mail1.wg.waii.com> References: <362BA1AD.E211A084@pp.inet.fi> NNTP-Posting-Host: rgs0.london.waii.com X-Newsreader: TIN [UNIX 1.3 unoff BETA 970424; IP12 IRIX 5.3] Path: news1.meer.net!news3.best.com!news1.best.com!su-news-hub1.bbnplanet.com!news.bbnplanet.com!newsfeed.corridex.com!ameritech.ais.net!jamie!ais.net!ameritech.net!uunet!in2.uu.net!diamond.waii.com!not-for-mail Xref: news1.meer.net comp.protocols.time.ntp:7373 Kimmo wrote: > I have a presentation to make about NTP and time in > computer networks. For introduction I need really strong > arguments for: why NTP is needed. > Who or what benefits of accurate time? > Is it the same if my time in our company network is same, > although different from "real time"? One of our servers > could start playing Stratum 1.... > We have several different computer systems in various servers. > We have databases and groupware products... > I think we need ntp. I just need arguments for selling it? These arguments were used to justify NTP in our company. Not everybody is sold on the idea, though. YMMV. I. The importance of clock synchronization in distributed networks. A. Time based security i. Most security schemes defeat replay attacks by using timestamped transactions. Therefore, they depend on synchronized clocks. ii. Logs on different machines are more easily compared if the timestamps are identical. B. Many distributed applications require synchronized clocks. i. "Make" on NFS-mounted file systems depends on accurate relative times of the NFS server and client. ii. Some parallel programming paradigms require clock synchronization between compute servers. IBM states that the SP series clocks must be synchronized. C. Synchronizing clocks between hosts helps insure against wildly incorrect clocks, an event which has caused major problems (above and beyond those previously mentioned) in the past. D. Synchronizing clocks automatically eliminates operator errors in trying to set the clocks by hand. II. Absolute time is better than relative time. A. Absolute time is legally tracable and can be admitted as evidence, should such be required. B. Different organizations can use different sources of absolute time, yet have their clocks synchronized. This eliminates the need for those organizations to share time services in order to internetwork. C. By using absolute time, there is never any question about which clock is "correct". Thus, if different organizations need to have synchronized clocks to support cooperative activities, no issues arise about which organization's clocks are "more correct". D. Real-time applications usually require absolute time for proper function. E. Many software protection schemes rely on the real-time clock to be reasonable accurate to determine when the software license expires. In at least one instance, a wildly erroneous clock on a Unix host caused some third party software to be disabled until new license codes could be received from the vendor, even after the host clock was corrected. F. Some financial applications require absolute time for auditability and accountability. III. Multiple radio clocks are desirable A. Redundant sources of absolute time provide for robustness during network failures, host downtimes, and radio clock failures. B. By owning its own radio clocks, the company avoids dependance on other outside sources for this critical, albeit minor, resource. C. Redundant sources, intelligently deployed, can reduce the network traffic required to keep different centers synchronized. D. Radio clocks are cheap insurance. A clock costs between $1600 US and $4500 US, depending on type and configuration, and requires almost no maintenance, yet helps to prevent many types of problems. -- Marc Brett +44 181 560 3160 Western Geophysical Marc.Brett@waii.com 455 London Road, Isleworth FAX: +44 181 847 5711 Middlesex TW7 5AB UK