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Implementing NTP on Cisco IOS XR Software
Network Time Protocol (NTP) is a protocol designed to time-synchronize devices within a network. The
Cisco IOS XR software implements NTPv4. NTPv4 retains backwards compatibility with the older
versions of NTP, including NTPv3 and NTPv2 but excluding NTPv1, which has been discontinued due
to security vulnerabilities.
This module describes the new and revised tasks you need to implement NTP on your Cisco IOS XR
network.
Note For more information about NTP
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Implementing NTP on Cisco IOS XR Software Prerequisites for Implementing NTP on Cisco IOS XR Software Prerequisites for Implementing NTP on Cisco IOS XR Software The following prerequisites are required to implement NTP in your network operating center (NOC): • You must be in a user group associated with a task group that includes the proper task IDs for CDP commands. Task IDs for commands are listed in the Cisco IOS XR Task ID Reference Guide. For detailed information about user groups and task
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software The communications between machines running NTP (known as “associations”) are usually statically configured; each machine is given the IP address of all machines with which it should form associations. Accurate timekeeping is made possible by exchanging NTP messages between each pair of machines with an association. However, in a LAN environment, NTP can be configured to use IP broadcast messages instead. Thi
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software The following are two most commonly used, poll-based association modes: • Client mode • Symmetric active mode The client and the symmetric active modes should be used when NTP is required to provide a high level of time accuracy and reliability. When a networking device is operating in the client mode, it polls its assigned time serving hosts for the current time. The networking device then picks a host from
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Command or Action Purpose server ip-address [version number][key key-id] Step 3 Forms a server association with another system. [minpoll interval] [maxpoll interval] [source interface-type interface-instance] [prefer] Example: RP/0/RP0/CPU0:router(config-ntp)# server 172.16.22.44 minpoll 8 maxpoll 12 peer ip-address [version number] [key key-id] Step 4 Forms a peer association with another system. [minpoll in
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software When a networking device is operating in the broadcastclient mode, it does not engage in any polling. Instead, it listens for NTP broadcast packets transmitted by broadcast time servers. Consequently, time accuracy can be marginally reduced, because time information flows only one way. Use the broadcast client command to set your networking device to listen for NTP broadcast packets propagated through a netwo
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Command or Action Purpose broadcast [destination ip-address][key key-id] Step 6 Configures the specified interface to send NTP broadcast [version number] packets. Example: RP/0/RP0/CPU0:(config-ntp-int)# broadcast destination 10.50.32.149 end Step 7 Saves configuration changes. or • When you issue the end command, the system prompts commit you to commit changes: Uncommitted changes found, commit them before e
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software If the source IP address matches the access lists for more than one access type, the first type is granted. If no access groups are specified, all access types are granted to all systems. If any access groups are specified, only the specified access types are granted. For details on NTP control queries, see RFC 1305 (NTP version 3). SUMMARY STEPS 1. configure 2. ntp 3. access-group {peer | query-only | serve
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Command or Action Purpose access-group {peer | query-only | serve | Step 3 Creates an access group and applies a basic IP access list to serve-only} access-list-name it. Example: RP/0/RP0/CPU0:router(config-ntp)# access-group peer access1 end Step 4 Saves configuration changes. or • When you issue the end command, the system prompts commit you to commit changes: Uncommitted changes found, commit them before e
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Configuring NTP Authentication This task explains how to configure NTP authentication. Note No specific command enables NTP; the first NTP configuration command that you issue enables NTP. NTP Authentication The encrypted NTP authentication scheme should be used when a reliable form of access control is required. Unlike the access-list-based restriction scheme that is based on IP addresses, the encrypted auth
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software DETAILED STEPS Command or Action Purpose Step 1 configure Enters global configuration mode. Example: RP/0/RP0/CPU0:router# configure Step 2 ntp Enters NTP configuration mode. Example: RP/0/RP0/CPU0:router(config)# ntp Step 3 authenticate Enables the NTP authentication feature. Example: RP/0/RP0/CPU0:router(config-ntp)# authenticate Step 4 authentication-key key-number md5 [clear | Defines the authentication k
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Disabling NTP Services on a Specific Interface This task explains how to disable NTP services on a specific interface. NTP services are disabled on all interfaces by default. NTP is enabled globally when any NTP commands are entered. You can selectively prevent NTP packets from being received through a specific interface by turning off NTP on a given interface. SUMMARY STEPS 1. configure 2. ntp 3. no interfac
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Command or Action Purpose no interface type instance Step 3 Disables NTP services on the specified interface. or interface type instance disable Example: RP/0/RP0/CPU0:router(config-ntp)# no interface pos 0/0/0/1 or RP/0/RP0/CPU0:router(config-ntp)# interface POS 0/0/0/1 disable end Step 4 Saves configuration changes. or • When you issue the end command, the system prompts commit you to commit changes: Uncomm
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Configuring the Source IP Address for NTP Packets This task explains how configure the source IP address for NTP packets. When the system sends an NTP packet, the source IP address is normally set to the address of the interface through which the NTP packet is sent. Note No specific command enables NTP; the first NTP configuration command that you issue enables NTP. SUMMARY STEPS 1. configure 2. ntp 3. source
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Command or Action Purpose source interface-type interface-instance Step 3 Configures an interface from which the IP source address will be taken. Example: Note This interface will be used for the source address for RP/0/RP0/CPU0:router(config-ntp)# source POS all packets sent to all destinations. If a source 0/0/0/1 address is to be used for a specific association, use the source parameter on the peer or serv
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Configuring the System as an Authoritative NTP Server This task explains how to configure the router as an authoritative NTP server. You can configure the router to act as an authoritative NTP server, even if the system is not synchronized to an outside time source Note No specific command enables NTP; the first NTP configuration command that you issue enables NTP. SUMMARY STEPS 1. configure 2. ntp 3. master
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Command or Action Purpose master stratum Step 3 Makes the router an authoritative NTP server. Note Use the master command with caution. It is very Example: easy to override valid time sources using this RP/0/RP0/CPU0:router(config-ntp)# master 9 command, especially if a low stratum number is configured. Configuring multiple machines in the same network with the master command can cause instability in timekeep
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software SUMMARY STEPS 1. configure 2. ntp 3. update-calendar 4. end or commit DETAILED STEPS Command or Action Purpose configure Step 1 Enters global configuration mode. Example: RP/0/RP0/CPU0:router# configure ntp Step 2 Enters NTP configuration mode. Example: RP/0/RP0/CPU0:router(config)# ntp update-calendar Step 3 Configures the system to update its hardware clock from the software clock at periodic intervals. Exa
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Implementing NTP on Cisco IOS XR Software How to Implement NTP on Cisco IOS XR Software Verifying the Status of the External Reference Clock This task explains how to verify the status of NTP components. Note The commands can be entered in any order. SUMMARY STEPS 1. show ntp associations [detail] [location node-id] 2. show ntp status [location node-id] DETAILED STEPS Command or Action Purpose show ntp associations [detail] [location Step 1 Displays the status of NTP associations. node-id] Examp
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Implementing NTP on Cisco IOS XR Software Configuration Examples for Implementing NTP on Cisco IOS XR Software Configuration Examples for Implementing NTP on Cisco IOS XR Software This section contains the following examples: • Configuring Poll-Based Associations: Example, page SMC-188 • Configuring Broadcast-Based Associations: Example, page SMC-188 • Configuring NTP Access Groups: Example, page SMC-188 • Configuring NTP Authentication: Example, page SMC-189 • Disabling NTP on an Interface: Exa
