HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 89

Configuring the Switch NTP Configuration Step 4 Step 5 Command or Action Purpose switch(config)# exit Returns to EXEC mode. switch# show running-config | include Verifies the time zone configuration. summer-time The following example adjusts the daylight savings time for the U.S. Pacific daylight time by 60 minutes starting the second Sunday in March at 2 a.m. and ending the first Sunday in November at 2 a.m: switch# configure terminal switch(config)# clock summer-time PDT 1 Sunday March 02:00 5 Sunday November 02:00 60 NTP Configuration A Network Time Protocol (NTP) server provides a precise time source (radio clock or atomic clock) to synchronize the system clocks of network devices. NTP uses User Datagram Protocol (UDP) on port 123 as its transport layer. An NTP server receives its time from a reference time source, such as a radio clock or atomic clock, attached to the server. NTP distributes this time across the network. All NTP communications use Universal Time Coordinated (UTC). About NTP In a large enterprise network, having one time standard for all network devices is critical for management reporting and event logging functions when trying to correlate interacting events logged across multiple devices. Many enterprise customers with extremely mission-critical networks maintain their own stratum-11 NTP source. Time synchronization happens when several frames are exchanged between clients and servers. The switches in client mode know the address of one or more NTP servers. The servers act as the time source and receive client synchronization requests. By configuring an IP address as a peer, the switch will obtain and provide time as required. The peer is capable of providing time on its own and is capable of having a server configured. If both these instances point to different time servers, your NTP service is more reliable. Even if the active server link is lost, you can still maintain the right time due to the presence of the peer. If an active server fails, a configured peer helps in providing the NTP time. Provide a direct NTP server association and configure a peer to ensure backup support if the active server fails. If you only configure a peer, the most accurate peer takes on the role of the NTP server and the other peer(s) acts as a peer(s). NTP Configuration Guidelines The following guidelines apply to all NTP configurations: • You should have a peer association with another switch only when you are sure that your clock is reliable (which means that you are a client of a reliable NTP server). • A peer configured alone takes on the role of a server and should be used as backup. If you have two servers, then you can have several switches point to one server, and the remaining switches to the other 1 NTP uses a hierarchical, layered system of levels of clock sources. Each level of this hierarchy is termed a stratum. Stratum 0 devices are atomic clocks, GPS clocks, or other radio clocks and are typically not directly connected to the network. Stratum 1 devices are directly attached to a Stratum 0 device as well as to the network and are referred to as time servers. OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 43