Implementing NTP on the Cisco IOS XR Software
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Contents
- Implementing NTP on the Cisco IOS XR Software
- Prerequisites for Implementing NTP on Cisco IOS XR Software
- Information About Implementing NTP
- How to Implement NTP on Cisco IOS XR Software
- Configuring Poll-Based Associations
- Configuring Broadcast-Based NTP Associates
- Configuring Multicast-Based NTP Associations
- Configuring NTP Access Groups
- Configuring NTP Authentication
- Disabling NTP Services on a Specific Interface
- Configuring the Source IP Address for NTP Packets
- Configuring the System as an Authoritative NTP Server
- Updating the Hardware Clock
- Verifying the Status of the External Reference Clock
- Examples
- Configuration Examples for Implementing NTP
- Additional References
Implementing NTP on the Cisco IOS XR Software
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 XR 12000 Series Router.
Table 1 Feature History for Implementing NTP on Cisco IOS XR Software Release
Modification
Release 3.2
This feature was introduced.
Release 3.3.0
No modification.
Release 3.4.0
No modification.
Release 3.5.0
No modification.
Release 3.6.0
No modification.
Release 3.7.0
No modification.
Release 3.8.0
Support was added for IPv6 addresses, VRFs, multicast-based associations, and burst and iburst modes for poll-based associations.
Release 3.9.0
No modification.
This module contains the following topics:
- Prerequisites for Implementing NTP on Cisco IOS XR Software
- Information About Implementing NTP
- How to Implement NTP on Cisco IOS XR Software
- Configuration Examples for Implementing NTP
- Additional References
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:
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.
Configuring Poll-Based Associations
SUMMARY STEPS
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):
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.
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:
DETAILED STEPSConfiguring Broadcast-Based NTP Associates
SUMMARY STEPSIn 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.
3. (Optional) broadcastdelay microseconds
4. interface type interface-path-id
6. broadcast [destination ip-address] [key key-id] [version number]
7. Use one of the following commands:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 broadcastdelay microseconds
Example:RP/0/0/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/0/0/CPU0:router(config-ntp)# interface POS 0/1/0/0Enters NTP interface configuration mode.
Step 5 broadcast client
Example:RP/0/0/CPU0:router(config-ntp-int)# broadcast clientConfigures 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/0/0/CPU0:router(config-ntp-int)# broadcast destination 10.50.32.149Configures the specified interface to send NTP broadcast packets.
Note Go to 5 to configure the interface to receive NTP broadcast packets.
Step 7 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp-int)# endor
RP/0/0/CPU0:router(config-ntp-int)# commitSaves 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
SUMMARY STEPSMulticast-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.
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:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 interface type interface-path-id [vrf vrf-name]
Example:RP/0/0/CPU0:router(config-ntp)# interface POS 0/1/0/0Enters NTP interface configuration mode.
Step 4 multicast client [ip-address]
Example:RP/0/0/CPU0:router(config-ntp-int)# multicast clientConfigures 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/0/0/CPU0:router(config-ntp-int)# multicast destination 224.0.1.1Configures 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 6 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# endor
RP/0/0/CPU0:router(config-ntp)# commitSaves 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
SUMMARY STEPS
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:
- 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.
- 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.
- serve-only—Allows only time requests from a system whose address passes the access list criteria.
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).
3. access-group{peer | query-only | serve | serve-only} access-list-name
4. Use one of the following commands:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 access-group{peer | query-only | serve | serve-only} access-list-name
Example:RP/0/0/CPU0:router(config-ntp)# access-group peer access1Creates an access group and applies a basic IPv4 or IPv6 access list to it.
Step 4 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# endor
RP/0/0/CPU0:router(config-ntp)# commitSaves 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
SUMMARY STEPSThis 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.
4. authentication-key key-number md5 [clear | encrypted] key-name
6. Use one of the following commands:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 authenticate
Example:RP/0/0/CPU0:router(config-ntp)# authenticateEnables the NTP authentication feature.
Step 4 authentication-key key-number md5 [clear | encrypted] key-name
Example:RP/0/0/CPU0:router(config-ntp)# authentication-key 42 md5 clear key1Defines the authentication keys.
Step 5 trusted-key key-number
Example:RP/0/0/CPU0:router(config-ntp)# trusted-key 42Defines trusted authentication keys.
Step 6 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# endor
RP/0/0/CPU0:router(config-ntp)# commitSaves 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
SUMMARY STEPSNTP 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.
3. Use one of the following commands:
4. Use one of the following commands:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# no interface pos 0/0/0/1or
RP/0/0/CPU0:router(config-ntp)# interface POS 0/0/0/1 disableDisables NTP services on the specified interface.
Step 4 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# endor
RP/0/0/CPU0:router(config-ntp)# commitSaves 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
SUMMARY STEPSBy 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.
3. source type interface-path-id
4. Use one of the following commands:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 source type interface-path-id
Example:RP/0/0/CPU0:router(config-ntp)# source POS 0/0/0/1Configures 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 4 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# endor
RP/0/0/CPU0:router(config-ntp)# commitSaves 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
SUMMARY STEPSYou 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.
4. Use one of the following commands:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 master stratum
Example:RP/0/0/CPU0:router(config-ntp)# master 9Makes 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 timekeeping if the machines do not agree on the time.
Step 4 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# endor
RP/0/0/CPU0:router(config-ntp)# commitSaves 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
SUMMARY STEPSOn 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.
4. Use one of the following commands:
DETAILED STEPS
Command or Action Purpose Step 1 configure
Example:RP/0/0/CPU0:router# configureEnters global configuration mode.
Step 2 ntp
Example:RP/0/0/CPU0:router(config)# ntpEnters NTP configuration mode.
Step 3 update-calendar
Example:RP/0/0/CPU0:router(config-ntp)# update-calendarConfigures the router t o update its system calendar from the software clock at periodic intervals.
Step 4 Use one of the following commands:
Example:RP/0/0/CPU0:router(config-ntp)# endor
RP/0/0/CPU0:router(config-ntp)# commitSaves 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
SUMMARY STEPSThis task explains how to verify the status of NTP components.
Note
The commands can be entered in any order.
1. show ntp associations [detail] [location node-id]
2. show ntp status [location node-id]
DETAILED STEPS
Command or Action Purpose Step 1 show ntp associations [detail] [location node-id]
Example:RP/0/0/CPU0:router# show ntp associationsDisplays the status of NTP associations.
Step 2 show ntp status [location node-id]
Example:RP/0/0/CPU0:router# show ntp statusDisplays the status of NTP.
Examples
The following is sample output from the show ntp associations command:
RP/0/0/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, ~ configuredThe following is sample output from the show ntp status command:
RP/0/0/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 agoConfiguration 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 172.19.69.1Configuring Broadcast-Based Associations: Example
The following example shows an NTP client configuration in which Gigabit Ethernet 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 GigabitEthernet 0/2/0/0 broadcast client exit broadcastdelay 2The following example shows an NTP server configuration where Gigabit Ethernet interface 0/2/0/2 is configured to be a broadcast server:
ntp interface GigabitEthernet 0/2/0/2 broadcastConfiguring 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 clientThe 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 224.0.1.1Configuring 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 exitConfiguring 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 2Disabling NTP on an Interface: Example
The following example shows an NTP configuration in which Gigabit Ethernet 0/2/0/0 interface is disabled:
ntp interface GigabitEthernet0/2/0/0 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 2Configuring 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/CPU0/0Additional References
Related Documents
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Clock Commands on the Cisco IOS XR Software module of Cisco IOS XR System Management Command Reference for the Cisco XR 12000 Series Router
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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
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