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Sidewinder G2 6.1.2 Administration Guide - Glossary of Technical ...

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Appendix B: Setting Up Network Time Protocol<br />

Overview <strong>of</strong> NTP<br />

596<br />

Figure 236: The<br />

<strong>Sidewinder</strong> <strong>G2</strong> as an NTP<br />

server—external time<br />

servers supply time to the<br />

<strong>Sidewinder</strong> <strong>G2</strong>, which<br />

passes time on to the<br />

internal system (multiple<br />

servers provide backup)<br />

As shown in Figure 236, the <strong>Sidewinder</strong> <strong>G2</strong> is receiving time from NTP servers<br />

on an external network and passing the time on to the internal network. This<br />

would be advantageous if your company required constant and precise time<br />

updates to within microseconds <strong>of</strong> world standard time.<br />

Important: Unlike the previous two configurations, an external-to-internal NTP<br />

configuration may introduce security concerns to the <strong>Sidewinder</strong> <strong>G2</strong> and thus to<br />

your network. Therefore, this configuration is only recommended for sites that need<br />

world standard time.<br />

Note: For the configuration shown in Figure 236, the router must be able to handle<br />

NTP traffic.<br />

time from the<br />

<strong>Sidewinder</strong> <strong>G2</strong><br />

time-feed<br />

internal<br />

network<br />

Router<br />

Servers on external network<br />

supply time to the <strong>Sidewinder</strong> <strong>G2</strong><br />

To pass a clock setting to the internal network, the external side <strong>of</strong> the<br />

<strong>Sidewinder</strong> <strong>G2</strong> needs to be configured as a client to the external clocks. The<br />

<strong>Sidewinder</strong> <strong>G2</strong>’s NTP client then takes the “tick” from the remote clock, and<br />

sends it to the on-board system clock. On the internal side <strong>of</strong> the <strong>Sidewinder</strong><br />

<strong>G2</strong>, the NTP server is enabled with the clock type set to “local.” This forces the<br />

<strong>Sidewinder</strong> <strong>G2</strong> to look to its internal clock for the time information, and<br />

configured as an internal server, pass the “tick” to the server on the internal<br />

burb interface.<br />

NTP must also be configured on each <strong>of</strong> the external time servers. For certified<br />

time servers, it is safe to assume that this has already been done correctly.<br />

An external NTP configuration is recommended only for sites that require time<br />

within microseconds <strong>of</strong> world standard time. This is achieved by configuring<br />

NTP on the <strong>Sidewinder</strong> <strong>G2</strong> to accept time signals from one or more certified<br />

time servers located outside your company network. For a list <strong>of</strong> certified time<br />

servers, check the following Web site:<br />

http://ntp.isc.org/bin/view/Servers/WebHome<br />

R

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