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CHAPTER 5 NTP DESIGN, CONFIGURATION, AND TROUBLESHOOTING
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NTP-Related Programs and Utilities
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In the network infrastructure environments (routers and switches), it s the show and debug commands that allow for the monitoring of individual NTP devices following their configuration. The show commands allow for the display of NTP status and associations, while the debug commands allow for identification of potential problems with synchronization, including those related to authentication. The Linux/Unix environments offer a series of programs and utilities, as defined in Table 5-3, that facilitate not only the operations but also the administration and management of NTP servers in those environments.
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Table 5-3. Linux/Unix NTP-Related Programs and Utilities Program Name ntpd/xntpd Program Description
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The NTP daemon. This program relies on the configuration statements within the ntp.conf, ntp.drift, and ntp.keys files to keep the server on which it is installed synchronized and its communications secure with the configured time source(s). The daemon operates on a server that s configured as a primary timeserver with a reference clock, or the daemon operates on an NTP client with the time source being a primary timeserver or even a high-level stratum server. The NTP query program. The use of the restrict command with the noquery flag within the ntp.conf file can prevent the local host from answering queries from another device that identifies the local host as a parameter (IP address or hostname) in this command. However, this utility is useful when it comes to NTP troubleshooting if the target host permits it. When the command is executed with the name of a target host as a parameter, it allows for subsequent execution of subcommands for display of the peers, NTP associations, clock variables to determine what kind of a clock is used by the timeserver, and more. A query utility on the order of ntpq but one that uses the mode field value of 7 (instead of 6 for ntpq) in the NTP message header. A utility that allows the setting of date and time via NTP This utility can be executed prior . to starting the NTP daemon to perform a one-time synchronization with a target server, in case the time on the host machine is significantly off. In the event that an administrator determines that running the NTP daemon poses a potential security risk on a client (you don t have much choice on a primary server!), the ntpdate utility can be periodically executed (run as a CRON job) to maintain the client synchronized with a target server. Don t expect a microsecond accuracy of the host clock with UTC, however, if you decide to use ntpdate as your only time synchronization tool, especially if it s run once a week! A utility that allows for the tracing of the chain of NTP servers up to the primary time source. This is not unlike the Traceroute utility in TCP/IP that allows for the tracing of a full route to a target host. A program for generating public and private keys that can be used with the Autokey protocol.
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The Novell NetWare environments offer programs similar to those of Unix but in the form of NetWare Loadable Modules (NLMs). For example, the NTPQ NLM, which corresponds to the ntpq Unix utility, can be executed to operate in an interactive mode (via the i switch) with the prompts and then written to and the commands read from the standard
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CHAPTER 5 NTP DESIGN, CONFIGURATION, AND TROUBLESHOOTING
output and input, respectively. Associations, peers, and numerous variables can be subsequently displayed and monitored. If synchronization is not working at all, it s advisable to execute the xtnpd/ntpd daemon with a d flag to enable debugging and to redirect the debugging output to syslog or to standard output (STDOUT).
NTP Configuration with Monitoring and Troubleshooting in Mind
In the Unix/Linux environments, the logging of NTP events is configured by specifying the location of the statistic collection directory in the ntp.conf file and by enabling the writing of the statistics records, which relate to the clock driver, peers, and loop filter statistics. Loop filter is part of the time-server model as specified in RFC 1305 s Determining Time and Frequency section in Appendix F. Listing 5-14 shows a sample section of the ntp.conf file, illustrating the statistics collection configuration.
Listing 5-14. Statistics Collection Configuration on ntp.conf #Define the location and enable the NTP statistics collection statsdir /var/ntp statistics loopstats peerstats clockstats filegen Apress_stats_set file Apress_NTP_stats type week The previous configuration identifies the /var/ntp directory for statistics collection related to the loop filter, the peers, and the clock driver. The filegen command further enables the management of the set of stat files, Apress_stats_set, and characterizes the individual files based on weekly collection intervals (use of the week variable with the type keyword). The reader is referred to each vendor s specific documentation on the subject of configuring NTP statistics collection. In the Novell NetWare environments, the function of statistics collection that is comparable to that shown in Listing 5-14 is accomplished via the XNTPD NLM. The XNTPD NLM offers long-term collection capabilities related to the clock driver, peers, and filter loop statistics. Statistics collection is most likely to be implemented on stratum 1 and 2 servers. As the NTP hierarchy progresses toward higher stratum levels from the primary timeservers through the networking infrastructure to the desktop environment the level of monitoring of NTP operations is bound to diminish. It is critical, however, that as part of routine network management you always ensure the primary timeserver s IP connectivity to the rest of the network. Subsequently, each NTP vendor will or should have management utilities that allow for monitoring the NTP health of the primary timeserver to verify that it continues to offer accurate synchronization service.
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