Cisco time synchronisation & summer time

Having accurate time configured on Cisco routers is important, if for nothing else being able to look through log files and understand when something happened is imperative. Configuring time on Cisco routers requires three different configuration elements:

• Configuring an external time source, usually NTP
• Configuring the device to adjust for summer time/daylight savings
• (Optionally) using the adjusted time in debugging and logs

Configuring a router to make use of NTP is straightforward, Browse the NTP Pool project website and locate a time source reasonably close to you. Once you have the address of a time server, issue the following configuration commands:

Router#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#ntp server uk.pool.ntp.org

The next step is to configure the timezone to be used on the router. To do this we give our timezone a name and specify the hour/minute offset from UTC:

Router(config)#clock timezone BST 0 0

If summer time is to be used, this can be configured with the “clock summer-time” commands. This assigns the adjustments to the timezone we created with the previous command. The command is a bit of a mouthful, but is fairly self explanatory. For the UK this is as follows:

clock summer-time BST recurring last Sun Mar 1:00 last Sun Oct 2:00

Finally, it’s likely you’ll want the adjusted time to appear in log files and debug output. This is configured with the following service options:

service timestamps debug datetime msec localtime
service timestamps log datetime msec localtime

With everything configured issuing “show clock detail” will show that the device is synchronising with NTP and our summer time / daylight savings configuration:

Router#sh clock detail
18:22:29.839 BST Wed Apr 16 2014
Time source is NTP
Summer time starts 01:00:00 GMT Sun Mar 30 2014
Summer time ends 02:00:00 BST Sun Oct 26 2014