OS6860(E)_AOS_8.1.1.R01_Switch_Management_Guide

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NTP Overview Configuring Network Time Protocol (NTP) Stratum Stratum is the term used to define the relative proximity of a node in a network to a time source (such as a radio clock). Stratum 1 is the server connected to the time source itself. (In most cases the time source and the stratum 1 server are in the same physical location.) An NTP client or server connected to a stratum 1 source would be stratum 2. A client or server connected to a stratum 2 machine would be stratum 3, and so on, as demonstrated in the diagram below: UTC Time Source Stratum 1 Stratum 2 Stratum 3 The farther away from stratum 1 a device is, the more likely there will be discrepancies or errors in the time adjustments done by NTP. A list of stratum 1 and 2 sources available to the public can be found on the Internet. Note. It is not required that NTP be connected to an officially recognized time source (for example, a radio clock). NTP can use any time source to synchronize time in the network. Using NTP in a Network NTP operates on the premise that there is one true standard time (defined by UTC), and that if several servers claiming synchronization to the standard time are in disagreement, then one or more of them must be out of synchronization or not functioning correctly. The stratum gradiation is used to qualify the accuracy of a time source along with other factors, such as advertised precision and the length of the network path between connections. NTP operates with a basic distrust of time information sent from other network entities, and is most effective when multiple NTP time sources are integrated together for checks and crosschecks. To achieve this end, there are several modes of operation that an NTP entity can use when synchronizing time in a network. These modes help predict how the entity behaves when requesting or sending time information, listed below: • A switch can be a client of an NTP server (usually of a lower stratum), receiving time information from the server but not passing it on to other switches. • A switch can be a client of an NTP server, and in turn be a server to another switch or switches. • A switch (regardless of its status as either a client or server) must be peered with another switch. Peering allows NTP entities in the network of the same stratum to regard each other as reliable sources of time and exchange time information. • The OmniSwitch by default will act as an NTP server and be able to respond to NTP client requests, and establish a client/server peering relationship. The OmniSwitch NTP server functionality allows the Omniswitch to establish an active peering relationship with another server, enable broadcast server functionality, disable a given IP for NTP and employ MD5 authentication for clients and active peers. page 11-6 OmniSwitch AOS Release 8 Switch Management Guide May 2014
Configuring Network Time Protocol (NTP) NTP Overview Examples of these are shown in the simple network diagram below: UTC Time Source Stratum 1 NTP Servers 1a 1b NTP Server/Clients Stratum 2 2a 2b Stratum 3 NTP Clients 3a 3b Servers 1a and 1b receive time information from, or synchronize with, a UTC time source such as a radio clock. (In most cases, these servers would not be connected to the same UTC source, though it is shown this way for simplicity.) Servers 1a and 1b become stratum 1 NTP servers and are peered with each other, allowing them to check UTC time information against each other. These machines support machines 2a and 2b as clients, and these clients are synchronized to the higher stratum servers 1a and 1b. Clients 2a and 2b are also peered with each other for time checks, and become stratum 2 NTP servers for more clients (3a and 3b, which are also peered). In this hierarchy, the stratum 1 servers synchronize to the most accurate time source available, then check the time information with peers at the same stratum. The stratum 2 machines synchronize to the stratum 1 servers, but do not send time information to the stratum 1 machines. Machines 2a and 2b in turn provide time information to the stratum 3 machines. It is important to consider the issue of robustness when selecting sources for time synchronization. It is suggested that at least three sources should be available, and at least one should be “close” to you in terms of network topology. It is also suggested that each NTP client is peered with at least three other same stratum clients, so that time information crosschecking is performed. When planning your network, it is helpful to use the following general rules: • It is usually not a good idea to synchronize a local time server with a peer (in other words, a server at the same stratum), unless the latter is receiving time updates from a source that has a lower stratum than from where the former is receiving time updates. This minimizes common points of failure. OmniSwitch AOS Release 8 Switch Management Guide May 2014 page 11-7
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Part No. 060391-10, Rev. A May 2014
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Contents About This Guide .........
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Contents Using the Switch as an FTP
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Contents Account and Password Polic
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Contents Authentication Trap ......
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Contents Firmware Upgrade Files ...
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About This Guide This OmniSwitch AO
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About This Guide Documentation Road
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About This Guide Related Documentat
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1 Logging Into the Switch Logging i
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Logging Into the Switch Quick Steps
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Logging Into the Switch Overview of
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Logging Into the Switch Accessing t
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Logging Into the Switch Setting the
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Logging Into the Switch Using Secur
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Logging Into the Switch Modifying t
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Logging Into the Switch Enabling th
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Logging Into the Switch Enabling th
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2 Managing System Files This chapte
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Managing System Files Switch Admini
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Managing System Files File and Dire
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Managing System Files Loading Softw
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Managing System Files Loading Softw
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Managing System Files Setting the S
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Managing System Files Setting the S
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3 Managing CMM Directory Content Th
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Managing CMM Directory Content CMM
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Managing CMM Directory Content Mana
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Managing CMM Directory Content Usin
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4 Using the CLI Alcatel-Lucent’s
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Using the CLI Command Entry Rules a
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Using the CLI Command Help -> sh vl
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Using the CLI Logging CLI Commands
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Using the CLI Customizing the Scree
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5 Working With Configuration Files
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Working With Configuration Files Tu
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Working With Configuration Files Qu
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Working With Configuration Files Cr
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Working With Configuration Files Cr
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6 Managing Switch User Accounts Swi
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Managing Switch User Accounts User
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Managing Switch User Accounts Overv
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Managing Switch User Accounts Creat
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Managing Switch User Accounts Setti
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Managing Switch User Accounts Multi
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7 Managing Switch Security Switch s
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Managing Switch Security Switch Sec
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Managing Switch Security Authentica
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Managing Switch Security Quick Step
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Managing Switch Security Setting Up
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Managing Switch Security Configurin
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8 Using WebView The switch can be m
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Using WebView WebView CLI Commands
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Page 137 and 138: 9 Using SNMP The Simple Network Man
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Configuring Virtual Chassis Configu
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Configuring Virtual Chassis Configu
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Configuring Virtual Chassis Display
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A Software License and Copyright St
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Alcatel-Lucent License Agreement Al
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B SNMP Trap Information This append
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SNMP Traps Table No. Trap Name Obje
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Index Symbols !! command 4-6 A aaa
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Index Network Time Protocol see NTP
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