Implementing NTP

Network Time Protocol (NTP) is a protocol designed to time-synchronize devices within a network. 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.

The Cisco implementation of NTP supports both IPv4 and IPv6 addresses and supports VRF.

This module describes the tasks you need to implement NTP on the Cisco IOS XR software.

For more information about NTP on the Cisco IOS XR software and complete descriptions of the NTP commands listed in this module, see Related Documents. To locate documentation for other commands that might appear in the course of running a configuration task, search online in Cisco IOS XR Commands Master List for the Cisco CRS Router.

Table 1 Feature History for Implementing NTP on Cisco IOS XR Software

Release

Modification

Release 2.0

This feature was introduced.

Release 3.8.0

Support was added for IPv6 addresses, VRFs, multicast-based associations, and burst and iburst modes for poll-based associations.

This module contains the following topics:

Prerequisites for Implementing NTP on Cisco IOS XR Software

You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Information About Implementing NTP

NTP synchronizes timekeeping among a set of distributed time servers and clients. This synchronization allows events to be correlated when system logs are created and other time-specific events occur.

NTP uses the User Datagram Protocol (UDP) as its transport protocol. All NTP communication uses Coordinated Universal Time (UTC). An NTP network usually receives its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server. NTP distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two machines to within a millisecond of each other.

NTP uses the concept of a “stratum” to describe how many NTP “hops” away a machine is from an authoritative time source. A “stratum 1” time server typically has an authoritative time source (such as a radio or atomic clock, or a GPS time source) directly attached, a “stratum 2” time server receives its time via NTP from a “stratum 1” time server, and so on.

NTP avoids synchronizing to a machine whose time may not be accurate, in two ways. First, NTP never synchronizes to a machine that is not synchronized itself. Second, NTP compares the time reported by several machines and does not synchronize to a machine whose time is significantly different than the others, even if its stratum is lower. This strategy effectively builds a self-organizing tree of NTP servers.

The Cisco implementation of NTP does not support stratum 1 service; in other words, it is not possible to connect to a radio or atomic clock (for some specific platforms, however, you can connect a GPS time-source device). We recommend that time service for your network be derived from the public NTP servers available in the IP Internet.

If the network is isolated from the Internet, the Cisco implementation of NTP allows a machine to be configured so that it acts as though it is synchronized via NTP, when in fact it has determined the time using other means. Other machines can then synchronize to that machine via NTP.

Several manufacturers include NTP software for their host systems, and a publicly available version for systems running UNIX and its various derivatives is also available. This software also allows UNIX-derivative servers to acquire the time directly from an atomic clock, which would subsequently propagate time information along to Cisco routers.

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.

The Cisco implementation of NTP supports three ways that a networking device can obtain NTP time information on a network:

  • By polling host servers
  • By listening to NTP broadcasts
  • By listening to NTP multicasts

In a LAN environment, NTP can be configured to use IP broadcast or multicast messages. As compared to polling, IP broadcast or multicast messages reduce configuration complexity, because each machine can simply be configured to send or receive broadcast or multicast messages. However, the accuracy of timekeeping is marginally reduced because the information flow is one-way only.

An NTP broadcast client listens for broadcast messages sent by an NTP broadcast server at a designated IPv4 address. The client synchronizes the local clock using the first received broadcast message.

An NTP multicast server periodically sends a message to a designated IPv4 or IPv6 local multicast group address. An NTP multicast client listens on this address for NTP messages.

The time kept on a machine is a critical resource, so we strongly recommend that you use the security features of NTP to avoid the accidental or malicious setting of incorrect time. Two mechanisms are available: an access list-based restriction scheme and an encrypted authentication mechanism.

When multiple sources of time (VINES, hardware clock, manual configuration) are available, NTP is always considered to be more authoritative. NTP time overrides the time set by any other method.

How to Implement NTP

Configuring Poll-Based Associations


Note

No specific command enables NTP; the first NTP configuration command that you issue enables NTP.

You can configure the following types of poll-based associations between the router and other devices (which may also be routers):

  • 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 all the polled time servers to synchronize with. Because the relationship that is established in this case is a client-host relationship, the host does not capture or use any time information sent by the local client device. This mode is most suited for file-server and workstation clients that are not required to provide any form of time synchronization to other local clients. Use the server command to individually specify the time-serving hosts that you want your networking device to consider synchronizing with and to set your networking device to operate in the client mode.

When a networking device is operating in the symmetric active mode, it polls its assigned time-serving hosts for the current time and it responds to polls by its hosts. Because this is a peer-to-peer relationship, the host also retains time-related information about the local networking device that it is communicating with. This mode should be used when there are several mutually redundant servers that are interconnected via diverse network paths. Most stratum 1 and stratum 2 servers on the Internet today adopt this form of network setup. Use the peer command to individually specify the time-serving hosts that you want your networking device to consider synchronizing with and to set your networking device to operate in the symmetric active mode.

When the router polls several other devices for the time, the router selects one device with which to synchronize.


Note

To configure a peer-to-peer association between the router and another device, you must also configure the router as a peer on the other device.

You can configure multiple peers and servers, but you cannot configure a single IP address as both a peer and a server at the same time.

To change the configuration of a specific IP address from peer to server or from server to peer, use the no form of the peer or server command to remove the current configuration before you perform the new configuration. If you do not remove the old configuration before performing the new configuration, the new configuration does not overwrite the old configuration.

SUMMARY STEPS

    1.    configure

    2.    ntp

    3.    server ip-address [version number] [key key-id] [minpoll interval] [maxpoll interval] [source type interface-path-id] [prefer] [burst] [iburst]

    4.    peer ip-address [version number] [key key-id] [minpoll interval] [maxpoll interval] [source type interface-path-id] [prefer]

    5.    Use one of the following commands:

    • end
    • commit


DETAILED STEPS
     Command or ActionPurpose
    Step 1 configure
          		 
    Step 2 ntp


    Example: 
    RP/0/RP0/CPU0:router(config)# ntp
     

    Enters NTP configuration mode.

     
    Step 3 server ip-address [version number] [key key-id] [minpoll interval] [maxpoll interval] [source type interface-path-id] [prefer] [burst] [iburst]


    Example: 
    RP/0/RP0/CPU0:router(config-ntp)# server 172.16.22.44 
    minpoll 8 maxpoll 12
     

    Forms a server association with another system. This step can be repeated as necessary to form associations with multiple devices.

     
    Step 4 peer ip-address [version number] [key key-id] [minpoll interval] [maxpoll interval] [source type interface-path-id] [prefer]


    Example: 
    RP/0/RP0/CPU0:router(config-ntp)# peer 192.168.22.33 
    minpoll 8 maxpoll 12 source tengige 0/0/0/1
     

    Forms a peer association with another system. This step can be repeated as necessary to form associations with multiple systems.

    Note   

    To complete the configuration of a peer-to-peer association between the router and the remote device, the router must also be configured as a peer on the remote device.

     
    Step 5Use one of the following commands:
    • end
    • commit


    Example: 
    RP/0/RP0/CPU0:router(config-ntp)# end

    or 

    RP/0/RP0/CPU0:router(config-ntp)# commit
     

    Saves configuration changes.

    • When you issue the end command, the system prompts you to commit changes: 

      Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

      • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

      • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

      • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

    • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

     

    Configuring Broadcast-Based NTP Associates

    In a broadcast-based NTP association, an NTP server propagates NTP broadcast packets throughout a network. Broadcast clients listen for the NTP broadcast packets propagated by the NTP server and do not engage in any polling.

    Broadcast-based NTP associations should be used when time accuracy and reliability requirements are modest and if your network is localized and has a large number of clients (more than 20). Broadcast-based NTP associations also are recommended for use on networks that have limited bandwidth, system memory, or CPU resources. Time accuracy is marginally reduced in broadcast-based NTP associations because information flows only one way.

    Use the broadcast client command to set your networking device to listen for NTP broadcast packets propagated through a network. For broadcast client mode to work, the broadcast server and its clients must be located on the same subnet. The time server that is transmitting NTP broadcast packets must be enabled on the interface of the given device using the broadcast command.

    Use the broadcast command to set your networking device to send NTP broadcast packets.


    Note

    No specific command enables NTP; the first NTP configuration command that you issue enables NTP.

    SUMMARY STEPS

      1.    configure

      2.    ntp

      3.    (Optional) broadcastdelay microseconds

      4.    interface type interface-path-id

      5.    broadcast client

      6.    broadcast [destination ip-address] [key key-id] [version number]

      7.    Use one of the following commands:

      • end
      • commit


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 configure
              		 
      Step 2 ntp


      Example: 
      RP/0/RP0/CPU0:router(config)# ntp
       

      Enters NTP configuration mode.

       
      Step 3 broadcastdelay microseconds


      Example: 
      RP/0/RP0/CPU0:router(config-ntp)# broadcastdelay 5000
              		(Optional)

      Adjusts the estimated round-trip delay for NTP broadcasts.

       
      Step 4 interface type interface-path-id


      Example: 
      RP/0/RP0/CPU0:router(config-ntp)# interface POS 0/1/0/0
       

      Enters NTP interface configuration mode.

       
      Step 5 broadcast client


      Example: 
      RP/0/RP0/CPU0:router(config-ntp-int)# broadcast client
       

      Configures the specified interface to receive NTP broadcast packets.

      Note   

      Go to 6 to configure the interface to send NTP broadcast packets.

       
      Step 6 broadcast [destination ip-address] [key key-id] [version number]


      Example: 
      RP/0/RP0/CPU0:router(config-ntp-int)# broadcast 
destination 10.50.32.149
       

      Configures the specified interface to send NTP broadcast packets.

      Note   

      Go to 5 to configure the interface to receive NTP broadcast packets.

       
      Step 7Use one of the following commands:
      • end
      • commit


      Example: 
      RP/0/RP0/CPU0:router(config-ntp-int)# end

      or 

      RP/0/RP0/CPU0:router(config-ntp-int)# commit
       

      Saves configuration changes.

      • When you issue the end command, the system prompts you to commit changes: 

        Uncommitted changes found, commit them before exiting(yes/no/cancel)?
[cancel]:

        • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

        • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

        • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

      • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

       

      Configuring Multicast-Based NTP Associations

      Multicast-based NTP associations should be used when time accuracy and reliability requirements are modest and if your network is localized and has a large number of clients (more than 20). Multicast-based NTP associations also are recommended for use on networks that have limited bandwidth, system memory, or CPU resources.

      When the router operates as an NTP multicast client, it listens for NTP multicast packets that are sent by an NTP multicast server to a designated IPv4 or IPv6 multicast group IP address.

      When the router operates as an NTP multicast server, it sends NTP multicast messages to a designated IPv4 or IPv6 multicast group IP address.


      Note

      No specific command enables NTP; the first NTP configuration command that you issue enables NTP.

      SUMMARY STEPS

        1.    configure

        2.    ntp

        3.    interface type interface-path-id [vrf vrf-name]

        4.    multicast client [ip-address]

        5.    multicast destination ip-address [key key-id] [version number] [ttl ttl]

        6.    Use one of the following commands:

        • end
        • commit


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 configure
                  		 
        Step 2 ntp


        Example: 
        RP/0/RP0/CPU0:router(config)# ntp
         

        Enters NTP configuration mode.

         
        Step 3 interface type interface-path-id [vrf vrf-name]


        Example: 
        RP/0/RP0/CPU0:router(config-ntp)# interface POS 0/1/0/0
         

        Enters NTP interface configuration mode.

         
        Step 4 multicast client [ip-address]


        Example: 
        RP/0/RP0/CPU0:router(config-ntp-int)# multicast client
         

        Configures the specified interface to listen for NTP multicast packets on the specified IPv4 or IPv6 address. If no IP address is specified, the interface listens on the default IPv4 address 224.0.1.1.

        Note   

        To configure the interface to send NTP multicast packets, go to 5

         
        Step 5 multicast destination ip-address [key key-id] [version number] [ttl ttl]


        Example: 
        RP/0/RP0/CPU0:router(config-ntp-int)# multicast destination 224.0.1.1
         

        Configures the specified interface to send NTP multicast packets to a specified IPv4 or IPv6 multicast group address.

        Note   

        To configure the interface to listen for NTP multicast packets, go to 4.

         
        Step 6Use one of the following commands:
        • end
        • commit


        Example: 
        RP/0/RP0/CPU0:router(config-ntp)# end

        or 

        RP/0/RP0/CPU0:router(config-ntp)# commit
         

        Saves configuration changes.

        • When you issue the end command, the system prompts you to commit changes: 

          Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

          • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

          • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

          • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

        • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

         

        Configuring NTP Access Groups


        Note

        No specific command enables NTP; the first NTP configuration command that you issue enables NTP.

        The access list-based restriction scheme allows you to grant or deny certain access privileges to an entire network, a subnet within a network, or a host within a subnet. NTP communication consists of time requests and control queries. A time request is a request for time synchronization from an NTP server. A control query is a request for configuration information from an NTP server.

        The access group options are scanned in the following order, from least restrictive to most restrictive:

        1. peer—Allows time requests and NTP control queries and allows the system to synchronize itself to a system whose address passes the access list criteria.
        2. serve—Allows time requests and NTP control queries, but does not allow the system to synchronize itself to a system whose address passes the access list criteria.
        3. serve-only—Allows only time requests from a system whose address passes the access list criteria.

        4. query-only—Allows only NTP control queries from a system whose address passes the access list criteria.

        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 | serve-only} access-list-name

          4.    Use one of the following commands:

          • end
          • commit


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 configure
                      		 
          Step 2 ntp


          Example: 
          RP/0/RP0/CPU0:router(config)# ntp
           

          Enters NTP configuration mode.

           
          Step 3 access-group{peer | query-only | serve | serve-only} access-list-name


          Example: 
          RP/0/RP0/CPU0:router(config-ntp)# access-group peer access1
           

          Creates an access group and applies a basic IPv4 or IPv6 access list to it.

           
          Step 4Use one of the following commands:
          • end
          • commit


          Example: 
          RP/0/RP0/CPU0:router(config-ntp)# end

          or 

          RP/0/RP0/CPU0:router(config-ntp)# commit
           

          Saves configuration changes.

          • When you issue the end command, the system prompts you to commit changes: 

            Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

            • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

            • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

            • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

          • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

           

          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.

          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 authentication scheme uses authentication keys and an authentication process to determine if NTP synchronization packets sent by designated peers or servers on a local network are deemed as trusted, before the time information that it carries along is accepted.

          The authentication process begins from the moment an NTP packet is created. A message authentication code (MAC) is computed using the MD5 Message Digest Algorithm and the MAC is embedded into an NTP synchronization packet. The NTP synchronization packet together with the embedded MAC and key number are transmitted to the receiving client. If authentication is enabled and the key is trusted, the receiving client computes the MAC in the same way. If the computed MAC matches the embedded MAC, the system is allowed to sync to the server that uses this key in its packets.

          After NTP authentication is properly configured, your networking device only synchronizes with and provides synchronization to trusted time sources.

          SUMMARY STEPS

            1.    configure

            2.    ntp

            3.    authenticate

            4.    authentication-key key-number md5 [clear | encrypted] key-name

            5.    trusted-key key-number

            6.    Use one of the following commands:

            • end
            • commit


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 configure
                          		 
            Step 2 ntp


            Example: 
            RP/0/RP0/CPU0:router(config)# ntp
             

            Enters NTP configuration mode.

             
            Step 3 authenticate


            Example: 
            RP/0/RP0/CPU0:router(config-ntp)# authenticate
             

            Enables the NTP authentication feature.

             
            Step 4 authentication-key key-number md5 [clear | encrypted] key-name


            Example: 
            RP/0/RP0/CPU0:router(config-ntp)# authentication-key 42 
md5 clear key1
             

            Defines the authentication keys.

            • Each key has a key number, a type, a value, and, optionally, a name. Currently the only key type supported is md5.
             
            Step 5 trusted-key key-number


            Example: 
            RP/0/RP0/CPU0:router(config-ntp)# trusted-key 42
             

            Defines trusted authentication keys.

            • If a key is trusted, this router only synchronizes to a system that uses this key in its NTP packets.
             
            Step 6Use one of the following commands:
            • end
            • commit


            Example: 
            RP/0/RP0/CPU0:router(config-ntp)# end

            or 

            RP/0/RP0/CPU0:router(config-ntp)# commit
             

            Saves configuration changes.

            • When you issue the end command, the system prompts you to commit changes: 

              Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

              • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

              • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

              • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

            • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

             

            Disabling 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.    Use one of the following commands:

              • no interface type interface-path-id
              • interface type interface-path-id disable

              4.    Use one of the following commands:

              • end
              • commit


            DETAILED STEPS
               Command or ActionPurpose
              Step 1 configure
                              		 
              Step 2 ntp


              Example: 
              RP/0/RP0/CPU0:router(config)# ntp
               

              Enters NTP configuration mode.

               
              Step 3 Use one of the following commands:
              • no interface type interface-path-id
              • interface type interface-path-id 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
               

              Disables NTP services on the specified interface.

               
              Step 4Use one of the following commands:
              • end
              • commit


              Example: 
              RP/0/RP0/CPU0:router(config-ntp)# end

              or 

              RP/0/RP0/CPU0:router(config-ntp)# commit
               

              Saves configuration changes.

              • When you issue the end command, the system prompts you to commit changes: 

                Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

                • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

                • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

                • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

              • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

               

              Configuring the Source IP Address for NTP Packets

              By default, the source IP address of an NTP packet sent by the router is the address of the interface through which the NTP packet is sent. Use this procedure to set a different source address.


              Note

              No specific command enables NTP; the first NTP configuration command that you issue enables NTP.

              SUMMARY STEPS

                1.    configure

                2.    ntp

                3.    source type interface-path-id

                4.    Use one of the following commands:

                • end
                • commit


              DETAILED STEPS
                 Command or ActionPurpose
                Step 1 configure
                                  		 
                Step 2 ntp


                Example: 
                RP/0/RP0/CPU0:router(config)# ntp
                 

                Enters NTP configuration mode.

                 
                Step 3 source type interface-path-id


                Example: 
                RP/0/RP0/CPU0:router(config-ntp)# source POS 0/0/0/1
                 

                Configures an interface from which the IP source address is taken.

                Note   

                This interface is used for the source address for all packets sent to all destinations. If a source address is to be used for a specific association, use the source keyword in the peer or server command shown in Configuring Poll-Based Associations.

                 
                Step 4Use one of the following commands:
                • end
                • commit


                Example: 
                RP/0/RP0/CPU0:router(config-ntp)# end

                or 

                RP/0/RP0/CPU0:router(config-ntp)# commit
                 

                Saves configuration changes.

                • When you issue the end command, the system prompts you to commit changes: 

                  Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

                  • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

                  • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

                  • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

                • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

                 

                Configuring the System 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 stratum

                  4.    Use one of the following commands:

                  • end
                  • commit


                DETAILED STEPS
                   Command or ActionPurpose
                  Step 1 configure
                                      		 
                  Step 2 ntp


                  Example: 
                  RP/0/RP0/CPU0:router(config)# ntp
                   

                  Enters NTP configuration mode.

                   
                  Step 3 master stratum


                  Example: 
                  RP/0/RP0/CPU0:router(config-ntp)# master 9
                   

                  Makes the router an authoritative NTP server.

                  Note   

                  Use the master command with caution. It is very easy to override valid time sources using this command, especially if a low stratum number is configured. Configuring multiple machines in the same network with the master command can cause instability in time keeping if the machines do not agree on the time.

                   
                  Step 4Use one of the following commands:
                  • end
                  • commit


                  Example: 
                  RP/0/RP0/CPU0:router(config-ntp)# end

                  or 

                  RP/0/RP0/CPU0:router(config-ntp)# commit
                   

                  Saves configuration changes.

                  • When you issue the end command, the system prompts you to commit changes: 

                    Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

                    • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

                    • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

                    • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

                  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

                   

                  Updating the Hardware Clock

                  On devices that have hardware clocks (system calendars), you can configure the hardware clock to be periodically updated from the software clock. This is advisable for devices using NTP, because the time and date on the software clock (set using NTP) is more accurate than the hardware clock. The time setting on the hardware clock has the potential to drift slightly over time.


                  Note

                  No specific command enables NTP; the first NTP configuration command that you issue enables NTP.

                  SUMMARY STEPS

                    1.    configure

                    2.    ntp

                    3.    update-calendar

                    4.    Use one of the following commands:

                    • end
                    • commit


                  DETAILED STEPS
                     Command or ActionPurpose
                    Step 1 configure
                                          		 
                    Step 2 ntp


                    Example: 
                    RP/0/RP0/CPU0:router(config)# ntp
                     

                    Enters NTP configuration mode.

                     
                    Step 3 update-calendar


                    Example: 
                    RP/0/RP0/CPU0:router(config-ntp)# update-calendar
                     

                    Configures the router t o update its system calendar from the software clock at periodic intervals.

                     
                    Step 4Use one of the following commands:
                    • end
                    • commit


                    Example: 
                    RP/0/RP0/CPU0:router(config-ntp)# end

                    or 

                    RP/0/RP0/CPU0:router(config-ntp)# commit
                     

                    Saves configuration changes.

                    • When you issue the end command, the system prompts you to commit changes: 

                      Uncommitted changes found, commit them before 
  exiting(yes/no/cancel)?
[cancel]:

                      • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

                      • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

                      • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

                    • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

                     

                    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 ActionPurpose
                      Step 1 show ntp associations [detail] [location node-id]


                      Example: 
                      RP/0/RP0/CPU0:router# show ntp associations
                       

                      Displays the status of NTP associations.

                       
                      Step 2 show ntp status [location node-id]


                      Example: 
                      RP/0/RP0/CPU0:router# show ntp status
                       

                      Displays the status of NTP.

                       

                      Examples

                      The following is sample output from the show ntp associations command: 

                      RP/0/RP0/CPU0:router# show ntp associations 
  
Tue Oct  7 11:22:46.839 JST 
   
      address         ref clock     st  when  poll reach  delay  offset    disp
*~192.168.128.5    10.81.254.131     2     1    64  377    7.98  -0.560   0.108
+~dead:beef::2 vrf testAA
                   171.68.10.80      3    20    64  377    6.00  -2.832   0.046
* sys_peer, # selected, + candidate, - outlayer, x falseticker, ~ configured

                      The following is sample output from the show ntp status command: 

                      RP/0/RP0/CPU0:router# show ntp status 
  
Tue Oct  7 11:22:54.023 JST 
  
Clock is synchronized, stratum 3, reference is 192.168.128.5
nominal freq is 1000.0000 Hz, actual freq is 1000.2725 Hz, precision is 2**24
reference time is CC95463C.9B964367 (11:21:48.607 JST Tue Oct  7 2008)
clock offset is -1.738 msec, root delay is 186.050 msec
root dispersion is 53.86 msec, peer dispersion is 0.09 msec
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is -0.0002724105 s/s
system poll interval is 64, last update was 66 sec ago

                      Configuration Examples for Implementing NTP

                      Configuring Poll-Based Associations: Example

                      The following example shows an NTP configuration in which the router’s system clock is configured to form a peer association with the time server host at IP address 192.168.22.33, and to allow the system clock to be synchronized by time server hosts at IP address 10.0.2.1 and 172.19.69.1: 

                      ntp
  server 10.0.2.1 minpoll 5 maxpoll 7
  peer 192.168.22.33

  server 172.19.69.1

                      Configuring Broadcast-Based Associations: Example

                      The following example shows an NTP client configuration in which interface 0/2/0/0 is configured to receive NTP broadcast packets, and the estimated round-trip delay between an NTP client and an NTP broadcast server is set to 2 microseconds: 

                      ntp 
  interface tengige 0/2/0/0
    broadcast client
    exit
  broadcastdelay 2

                      The following example shows an NTP server configuration where interface 0/2/0/2 is configured to be a broadcast server: 

                      ntp 
  interface tengige 0/2/0/2
    broadcast

                      Configuring Multicast-Based Associations: Example

                      The following example shows an NTP multicast client configuration where 10-Gigabit Ethernet interface 0/1/1/0 is configured to be a multicast client and to join the default multicast group (IPv4 address 224.0.1.1): 

                      ntp interface TenGigE 0/1/1/0
  multicast client

                      The following example shows an NTP multicast server configuration where 10-Gigabit Ethernet interface 0/1/1/0 is configured to be a multicast server: 

                      ntp interface TenGigE 0/1/1/0
  multicast destination 224.0.1.1

                      Configuring NTP Access Groups: Example

                      The following example shows a NTP access group configuration where the following access group restrictions are applied:

                      • Peer restrictions are applied to IP addresses that pass the criteria of the access list named peer-acl.
                      • Serve restrictions are applied to IP addresses that pass the criteria of access list named serve-acl.
                      • Serve-only restrictions are applied to IP addresses that pass the criteria of the access list named serve-only-acl.
                      • Query-only restrictions are applied to IP addresses that pass the criteria of the access list named query-only-acl. 
                      ntp
  peer 10.1.1.1
  peer 10.1.1.1
  peer 10.2.2.2
  peer 10.3.3.3
  peer 10.4.4.4
  peer 10.5.5.5
  peer 10.6.6.6
  peer 10.7.7.7
  peer 10.8.8.8
  access-group peer peer-acl
  access-group serve serve-acl
  access-group serve-only serve-only-acl
  access-group query-only query-only-acl
  exit
ipv4 access-list peer-acl
  10 permit ip host 10.1.1.1 any
  20 permit ip host 10.8.8.8 any
  exit
ipv4 access-list serve-acl
  10 permit ip host 10.4.4.4 any
  20 permit ip host 10.5.5.5 any
  exit
ipv4 access-list query-only-acl
  10 permit ip host 10.2.2.2 any
  20 permit ip host 10.3.3.3 any
  exit
ipv4 access-list serve-only-acl
  10 permit ip host 10.6.6.6 any
  20 permit ip host 10.7.7.7 any
  exit

                      Configuring NTP Authentication: Example

                      The following example shows an NTP authentication configuration. In this example, the following is configured:

                      • NTP authentication is enabled.
                      • Two authentication keys are configured (key 2 and key 3).
                      • The router is configured to allow its software clock to be synchronized with the clock of the peer (or vice versa) at IP address 10.3.32.154 using authentication key 2.
                      • The router is configured to allow its software clock to be synchronized with the clock by the device at IP address 10.32.154.145 using authentication key 3.
                      • The router is configured to synchronize only to systems providing authentication key 3 in their NTP packets. 
                      ntp
  authenticate
  authentication-key 2 md5 encrypted 06120A2D40031D1008124
  authentication-key 3 md5 encrypted 1311121E074110232621
  trusted-key 3
  server 10.3.32.154 key 3
  peer 10.32.154.145 key 2

                      Disabling NTP on an Interface: Example

                      The following example shows an NTP configuration in which 0/2/0/0 interface is disabled: 

                      ntp
  interface tengige 0/2/0/0  
    disable
    exit
  authentication-key 2 md5 encrypted 06120A2D40031D1008124
  authentication-key 3 md5 encrypted 1311121E074110232621
  authenticate
  trusted-key 3
  server 10.3.32.154 key 3
  peer 10.32.154.145 key 2

                      Configuring the Source IP Address for NTP Packets: Example

                      The following example shows an NTP configuration in which Ethernet management interface 0/0/CPU0/0 is configured as the source address for NTP packets: 

                      ntp 
  authentication-key 2 md5 encrypted 06120A2D40031D1008124
  authentication-key 3 md5 encrypted 1311121E074110232621
  authenticate
  trusted-key 3
  server 10.3.32.154 key 3
  peer 10.32.154.145 key 2
  source MgmtEth0/0/CPU0/0

                      Configuring the System as an Authoritative NTP Server: Example

                      The following example shows a NTP configuration in which the router is configured to use its own NTP master clock to synchronize with peers when an external NTP source becomes unavailable: 

                      ntp 
  master 6

                      Updating the Hardware Clock: Example

                      The following example shows an NTP configuration in which the router is configured to update its hardware clock from the software clock at periodic intervals: 

                      ntp 
  server 10.3.32.154
  update-calendar

                      Additional References

                      The following sections provide references related to implementing NTP on Cisco IOS XR software.

                      Related Documents

                      Related Topic

                      Document Title

                      Cisco IOS XR clock commands

                      Clock Commands on the Cisco IOS XR Software module of Cisco IOS XR System Management Command Reference for the Cisco CRS Router

                      Cisco IOS XR NTP commands

                      NTP Commands on module of Cisco IOS XR System Management Command Reference for the Cisco CRS Router

                      Information about getting started with Cisco IOS XR Software

                      Cisco IOS XR Getting Started Guide for the Cisco CRS Router

                      Cisco IOS XR master command index

                      Cisco IOS XR Commands Master List for the Cisco CRS Router

                      Information about user groups and task IDs

                      Configuring AAA Services on the Cisco IOS XR Software module of Cisco IOS XR System Security Configuration Guide for the Cisco CRS Router

                      Standards

                      Standards

                      Title

                      No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

                      		—

                      MIBs

                      MIBs

                      MIBs Link
                      —

                      To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http:/​/​cisco.com/​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml

                      RFCs

                      RFCs

                      Title

                      RFC 1059

                      Network Time Protocol, Version 1: Specification and Implementation

                      RFC 1119

                      Network Time Protocol, Version 2: Specification and Implementation

                      RFC 1305

                      Network Time Protocol, Version 3: Specification, Implementation, and Analysis

                      Technical Assistance

                      Description

                      Link

                      The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

                      http:/​/​www.cisco.com/​cisco/​web/​support/​index.html