Recipe 14.3 Setting the Time Zone

14.3.1 Problem

You want to change the time zone on the router.

14.3.2 Solution

To configure the router's local time zone, use the following configuration command:

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#clock timezone EST -5
Router(config)#end
Router#

The clock timezone configuration command accepts any freeform zone name (EST, PST, Eastern, etc.) followed by an offset from the UTC (-24 to 24 hours), and an optional offset from UTC in minutes for areas that require it.

14.3.3 Discussion

By default, the router uses UTC, also called Coordinated Universal Time. UTC, formerly known as Greenwich Mean Time (GMT), has become the worldwide standard for time and date. The principles for calculating local time zones from UTC are the same as for GMT. The only difference is that UTC is based on precise atomic clocks, shortwave radio signals, and satellites to ensure accuracy. These devices do not actually need to be located in Greenwich, England.

It is useful to set the router's internal system clock to display the time in the local time zone. North American clocks set to UTC, for example, display the time between five and eight hours ahead of the local time. This means that somebody reading the clock has to do some mental arithmetic to translate to local time, which is sometimes awkward and makes correlating the times of network problems more difficult than it needs to be.

You can view the current time zone information with the show clock detail command:

Router>show clock detail
14:27:31.415 EST Wed Mar 9 2003
Time source is NTP
Router>

Many organizations choose to configure all of their routers to the same time zone to make problem correlation easier, regardless of router location. The network administrators will configure all of their routers to the same time zone, even if they are physically located in a different part of the world. We recommend doing this because it simplifies troubleshooting by eliminating the need to do a lot of mental arithmetic that can unnecessarily slow down an already difficult and stressful situation.

Table 14-1 shows the configuration for several of the most commonly used time zones in North America.

Table 14-1. North American time zones

Time Zone

Abbr.

Offset from UTC

Configuration Command

Hawaiian Standard Time

HST

UTC -10

clock timezone HST -10

Alaska Standard Time

AKST

UTC -9

clock timezone AKST -9

Pacific Standard Time

PST

UTC -8

clock timezone PST -8

Mountain Standard Time

MST

UTC -7

clock timezone MST -7

Central Standard Time

CST

UTC -6

clock timezone CST -6

Eastern Standard Time

EST

UTC -5

clock timezone EST -5

Atlantic Standard Time

AST

UTC -4

clock timezone AST -4

Newfoundland Standard Time

NST

UTC -3.5

clock timezone NST -3 30

Table 14-1. North American time zones
Time Zone	Abbr.	Offset from UTC	Configuration Command
Hawaiian Standard Time	HST	UTC -10	clock timezone HST -10
Alaska Standard Time	AKST	UTC -9	clock timezone AKST -9
Pacific Standard Time	PST	UTC -8	clock timezone PST -8
Mountain Standard Time	MST	UTC -7	clock timezone MST -7
Central Standard Time	CST	UTC -6	clock timezone CST -6
Eastern Standard Time	EST	UTC -5	clock timezone EST -5
Atlantic Standard Time	AST	UTC -4	clock timezone AST -4
Newfoundland Standard Time	NST	UTC -3.5	clock timezone NST -3 30

14.3.4 See Also

Recipe 14.4; Recipe 14.5

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