Synchronize your device with a trusted time source by using the Network Time Protocol (NTP) or changing the system time before you run it on a live network. Various tasks, including network management, charging, auditing, and distributed computing depend on an accurate system time setting, because the timestamps of system messages and logs use the system time.

Overview

NTP is typically used in large networks to dynamically synchronize time among network devices. It guarantees higher clock accuracy than manual system clock setting. In a small network that does not require high clock accuracy, you can keep time synchronized among devices by changing their system clocks one by one.

NTP runs over UDP and uses UDP port 123.

NOTE:

NTP is supported by the following Layer 3 interfaces:

· Layer 3 Ethernet interfaces.

· Layer 3 Ethernet subinterfaces.

· VLAN interfaces.

· Tunnel interfaces.

How NTP works

Figure 1 shows how NTP synchronizes the system time between two devices (Device A and Device B, in this example). Assume that:

· Prior to the time synchronization, the time is set to 10:00:00 am for Device A and 11:00:00 am for Device B.

· Device B is used as the NTP server. Device A is to be synchronized to Device B.

· It takes 1 second for an NTP message to travel from Device A to Device B, and from Device B to Device A.

· It takes 1 second for Device B to process the NTP message.

Figure 1 Basic work flow

The synchronization process is as follows:

1. Device A sends Device B an NTP message, which is timestamped when it leaves Device A. The time stamp is 10:00:00 am (T1).

2. When this NTP message arrives at Device B, Device B adds a timestamp showing the time when the message arrived at Device B. The timestamp is 11:00:01 am (T2).

3. When the NTP message leaves Device B, Device B adds a timestamp showing the time when the message left Device B. The timestamp is 11:00:02 am (T3).

4. When Device A receives the NTP message, the local time of Device A is 10:00:03 am (T4).

Up to now, Device A can calculate the following parameters based on the timestamps:

· The roundtrip delay of the NTP message: Delay = (T4 – T1) – (T3 – T2) = 2 seconds.

· Time difference between Device A and Device B: Offset = [ (T2 – T1) + (T3 – T4) ] /2 = 1 hour.

Based on these parameters, Device A can be synchronized to Device B.

This is only a rough description of the work mechanism of NTP. For more information, see the related protocols and standards.

NTP architecture

NTP uses stratums 1 to 16 to define clock accuracy, as shown in Figure 2. A lower stratum value represents higher accuracy. Clocks at stratums 1 through 15 are in synchronized state, and clocks at stratum 16 are not synchronized.

Figure 2 NTP architecture

A stratum 1 NTP server gets its time from an authoritative time source, such as an atomic clock. It provides time for other devices as the primary NTP server. A stratum 2 time server receives its time from a stratum 1 time server, and so on.

To ensure time accuracy and availability, you can specify multiple NTP servers for a device. The device selects an optimal NTP server as the clock source based on parameters such as stratum. The clock that the device selects is called the reference source. For more information about clock selection, see the related protocols and standards.

If the devices in a network cannot synchronize to an authoritative time source, you can perform the following tasks:

· Select a device that has a relatively accurate clock from the network.

· Use the local clock of the device as the reference clock to synchronize other devices in the network.

Association modes

NTP supports the following association modes:

· Client/server mode

· Symmetric active/passive mode

· Broadcast mode

· Multicast mode

Table 1 NTP association modes

Mode	Working process	Principle	Application scenario
Client/server	On the client, specify the IP address of the NTP server. A client sends a clock synchronization message to the NTP servers. Upon receiving the message, the servers automatically operate in server mode and send a reply. If the client can be synchronized to multiple time servers, it selects an optimal clock and synchronizes its local clock to the optimal reference source after receiving the replies from the servers.	A client can synchronize to a server, but a server cannot synchronize to a client.	As Figure 2 shows, this mode is intended for configurations where devices of a higher stratum synchronize to devices with a lower stratum.
Symmetric active/passive	On the symmetric active peer, specify the IP address of the symmetric passive peer. A symmetric active peer periodically sends clock synchronization messages to a symmetric passive peer. The symmetric passive peer automatically operates in symmetric passive mode and sends a reply. If the symmetric active peer can be synchronized to multiple time servers, it selects an optimal clock and synchronizes its local clock to the optimal reference source after receiving the replies from the servers.	A symmetric active peer and a symmetric passive peer can be synchronized to each other. If both of them are synchronized, the peer with a higher stratum is synchronized to the peer with a lower stratum.	As Figure 2 shows, this mode is most often used between servers with the same stratum to operate as a backup for one another. If a server fails to communicate with all the servers of a lower stratum, the server can still synchronize to the servers of the same stratum.
Broadcast	A server periodically sends clock synchronization messages to the broadcast address 255.255.255.255. Clients listen to the broadcast messages from the servers to synchronize to the server according to the broadcast messages. When a client receives the first broadcast message, the client and the server start to exchange messages to calculate the network delay between them. Then, only the broadcast server sends clock synchronization messages.	A broadcast client can synchronize to a broadcast server, but a broadcast server cannot synchronize to a broadcast client.	A broadcast server sends clock synchronization messages to synchronize clients in the same subnet. As Figure 2 shows, broadcast mode is intended for configurations involving one or a few servers and a potentially large client population. The broadcast mode has a lower time accuracy than the client/server and symmetric active/passive modes because only the broadcast servers send clock synchronization messages.
Multicast	A multicast server periodically sends clock synchronization messages to the user-configured multicast address. Clients listen to the multicast messages from servers and synchronize to the server according to the received messages.	A multicast client can synchronize to a multicast server, but a multicast server cannot synchronize to a multicast client.	A multicast server can provide time synchronization for clients in the same subnet or in different subnets. The multicast mode has a lower time accuracy than the client/server and symmetric active/passive modes.

In this document, an "NTP server" or a "server" refers to a device that operates as an NTP server in client/server mode. Time servers refer to all the devices that can provide time synchronization, including NTP servers, NTP symmetric peers, broadcast servers, and multicast servers.

NTP security

To improve time synchronization security, NTP provides the access control and authentication functions.

NTP access control

You can control NTP access by using an ACL. The access rights are in the following order, from least restrictive to most restrictive:

· Peer—Allows time requests and NTP control queries (such as alarms, authentication status, and time server information) and allows the local device to synchronize itself to a peer device.

· Server—Allows time requests and NTP control queries, but does not allow the local device to synchronize itself to a peer device.

· Synchronization—Allows only time requests from a system whose address passes the access list criteria.

· Query—Allows only NTP control queries from a peer device to the local device.

When the device receives an NTP request, it matches the request against the access rights in the order from the least restrictive to the most restrictive: peer, server, synchronization, and query.

· If no NTP access control is configured, the peer access right applies.

· If the IP address of the peer device matches a permit statement in an ACL, the access right is granted to the peer device. If a deny statement or no ACL is matched, no access right is granted.

· If no ACL is specified for an access right or the ACL specified for the access right is not created, the access right is not granted.

· If none of the ACLs specified for the access rights is created, the peer access right applies.

· If none of the IPv4 ACLs specified for the access rights contains rules, no access right is granted.

This feature provides minimal security for a system running NTP. A more secure method is NTP authentication.

NTP authentication

Use this feature to authenticate the NTP messages for security purposes. If an NTP message passes authentication, the device can receive it and get time synchronization information. If not, the device discards the message. This function makes sure the device does not synchronize to an unauthorized time server.

Figure 3 NTP authentication

As shown in Figure 3, NTP authentication is performed as follows:

1. The sender uses the key identified by the key ID to calculate a digest for the NTP message through the MD5 algorithm. Then it sends the calculated digest together with the NTP message and key ID to the receiver.

2. Upon receiving the message, the receiver performs the following actions:

a. Finds the key according to the key ID in the message.

b. Uses the key and the MD5 algorithm to calculate the digest for the message.

c. Compares the digest with the digest contained in the NTP message.

- If they are different, the receiver discards the message.

- If they are the same, the local device determines whether the sender is allowed to use the authentication ID. If the sender is allowed to use the authentication ID, the receiver accepts the message. If the sender is not allowed to use the authentication ID, the receiver discards the message.

Protocols and standards

· RFC 1305, Network Time Protocol (Version 3) Specification, Implementation and Analysis

· RFC 5905, Network Time Protocol Version 4: Protocol and Algorithms Specification

Configuration restrictions and guidelines

When you configure NTP, follow these restrictions and guidelines:

· You cannot configure both NTP and SNTP on the same device.

· Do not configure NTP on an aggregate member port.

· The NTP service and SNTP service are mutually exclusive. You can only enable either NTP service or SNTP service at a time.

· To ensure time synchronization accuracy, do not specify more than one reference source. Doing so might cause frequent time changes or even synchronization failures.

Configuration task list

Tasks at a glance
(Required.) Enabling the NTP service
(Required.) Perform one or both of the following tasks: · Configuring NTP association modes · Configuring the local clock as a reference source
(Optional.) Configuring access control rights
(Optional.) Configuring NTP authentication
(Optional.) Configuring NTP optional parameters

Enabling the NTP service

Step	Command	Remarks
1. Enter system view.	system-view	N/A
1. Enable the NTP service.	ntp-service enable	By default, the NTP service is not enabled.

Configuring NTP association modes

This section describes how to configure NTP association modes.

Configuring NTP in client/server mode

When the device operates in client/server mode, specify the IP address for the server on the client.

Follow these guidelines when you configure an NTP client:

· A server must be synchronized by other devices or use its local clock as a reference source before synchronizing an NTP client. Otherwise, the client will not be synchronized to the NTP server.

· If the stratum level of a server is higher than or equal to a client, the client will not synchronize to that server.

· You can configure multiple servers by repeating the ntp-service unicast-server and ntp-service ipv6 unicast-server commands.

To configure an NTP client:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Specify an NTP server for the device.	· Specify an NTP server for the device: ntp-service unicast-server { server-name \| ip-address } [ authentication-keyid keyid \| priority \| source interface-type interface-number \| version number ] * · Specify an IPv6 NTP server for the device: ntp-service ipv6 unicast-server { server-name \| ipv6-address } [ authentication-keyid keyid \| priority \| source interface-type interface-number ] *	By default, no NTP server is specified for the device.

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Specify an NTP server for the device.

· Specify an NTP server for the device:
ntp-service unicast-server { server-name | ip-address } [ authentication-keyid keyid | priority | source interface-type interface-number | version number ] *

· Specify an IPv6 NTP server for the device:
ntp-service ipv6 unicast-server { server-name | ipv6-address } [ authentication-keyid keyid | priority | source interface-type interface-number ] *

By default, no NTP server is specified for the device.

Configuring NTP in symmetric active/passive mode

When the device operates in symmetric active/passive mode, specify on a symmetric-active peer the IP address for a symmetric-passive peer.

Follow these guidelines when you configure a symmetric-active peer:

· Execute the ntp-service enable command on a symmetric passive peer to enable NTP. Otherwise, the symmetric-passive peer will not process NTP messages from a symmetric-active peer.

· Either the symmetric-active peer, or the symmetric-passive peer, or both of them must be in synchronized state. Otherwise, their time cannot be synchronized.

· You can configure multiple symmetric-passive peers by repeating the ntp-service unicast-peer or ntp-service ipv6 unicast-peer command.

To configure a symmetric-active peer:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Specify a symmetric-passive peer for the device.	· Specify a symmetric-passive peer: ntp-service unicast-peer { peer-name \| ip-address } [ authentication-keyid keyid \| priority \| source interface-type interface-number \| version number ] * · Specify an IPv6 symmetric-passive peer: ntp-service ipv6 unicast-peer { peer-name \| ipv6-address } [ authentication-keyid keyid \| priority \| source interface-type interface-number ] *	By default, no symmetric-passive peer is specified.

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Specify a symmetric-passive peer for the device.

· Specify a symmetric-passive peer:
ntp-service unicast-peer { peer-name | ip-address } [ authentication-keyid keyid | priority | source interface-type interface-number | version number ] *

· Specify an IPv6 symmetric-passive peer:
ntp-service ipv6 unicast-peer { peer-name | ipv6-address } [ authentication-keyid keyid | priority | source interface-type interface-number ] *

By default, no symmetric-passive peer is specified.

Configuring NTP in broadcast mode

A broadcast server must be synchronized by other devices or use its local clock as a reference source before synchronizing a broadcast client. Otherwise, the broadcast client will not be synchronized to the broadcast server.

Configure NTP in broadcast mode on both broadcast server and client.

Configuring a broadcast client

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	Enter the interface for receiving NTP broadcast messages.
3. Configure the device to operate in broadcast client mode.	ntp-service broadcast-client	By default, the device does not operate in broadcast client mode. After you execute the command, the device receives NTP broadcast messages from the specified interface.

Configuring the broadcast server

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	Enter the interface for sending NTP broadcast messages.
3. Configure the device to operate in NTP broadcast server mode.	ntp-service broadcast-server [ authentication-keyid keyid \| version number ] *	By default, the device does not operate in broadcast server mode. After you execute the command, the device sends NTP broadcast messages from the specified interface.

Configuring NTP in multicast mode

A multicast server must be synchronized by other devices or use its local clock as a reference source before synchronizing a multicast client. Otherwise, the multicast client will not be synchronized to the multicast server.

Configure NTP in multicast mode on both a multicast server and client.

Configuring a multicast client

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	Enter the interface for receiving NTP multicast messages.
3. Configure the device to operate in multicast client mode.	· Configure the device to operate in multicast client mode: ntp-service multicast-client [ ip-address ] · Configure the device to operate in IPv6 multicast client mode: ntp-service ipv6 multicast-client ipv6-multicast-address	By default, the device does not operate in multicast server mode. After you execute the command, the device receives NTP multicast messages from the specified interface.

Configuring the multicast server

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	Enter the interface for sending NTP multicast message.
3. Configure the device to operate in multicast server mode.	· Configure the device to operate in multicast server mode: ntp-service multicast-server [ ip-address ] [ authentication-keyid keyid \| ttl ttl-number \| version number ] * · Configure the device to operate in multicast server mode: ntp-service ipv6 multicast-server ipv6-multicast-address [ authentication-keyid keyid \| ttl ttl-number ] *	By default, the device does not operate in multicast server mode. After you execute the command, the device receives NTP multicast messages from the specified interface.

Configuring access control rights

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Configure the right for peer devices to access the NTP services on the local device.	· Configure the right for peer devices to access the IPv4 NTP services on the local device: ntp-service access { peer \| query \| server \| synchronization } acl ipv4-acl-number · Configure the right for peer devices to access the IPv6 NTP services on the local device: ntp-service ipv6 { peer \| query \| server \| synchronization } acl ipv6-acl-number	By default, the right for peer devices to access the NTP services on the local device is peer.

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Configure the right for peer devices to access the NTP services on the local device.

· Configure the right for peer devices to access the IPv4 NTP services on the local device:
ntp-service access { peer | query | server | synchronization } acl ipv4-acl-number

· Configure the right for peer devices to access the IPv6 NTP services on the local device:
ntp-service ipv6 { peer | query | server | synchronization } acl ipv6-acl-number

By default, the right for peer devices to access the NTP services on the local device is peer.

Before you configure the NTP service access control right to the local device, create and configure an ACL associated with the access control right. For more information about ACL, see ACL and QoS Configuration Guide.

Configuring NTP authentication

This section provides instructions for configuring NTP authentication.

Configuring NTP authentication in client/server mode

To ensure a successful NTP authentication, configure the same authentication key ID and key on the server and client. Make sure the peer device is allowed to use the key ID for authentication on the local device.

To configure NTP authentication for a client:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.
5. Associate the specified key with an NTP server.	· Associate the specified key with an NTP server: ntp-service unicast-server { server-name \| ip-address } authentication-keyid keyid · Associate the specified key with an IPv6 NTP server: ntp-service ipv6 unicast-server { server-name \| ipv6-address } authentication-keyid keyid	By default, a trusted key is not associated with an NTP server.

To configure NTP authentication for a server:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.

NTP authentication results differ when different configurations are performed on client and server. For more information, see Table 2. (N/A in the table means that whether the configuration is performed does not make any difference.)

Table 2 NTP authentication results

Client			Server		Authentication result
Enable NTP authentication	Configure a key and configure it as a trusted key	Associate the key with an NTP server	Enable NTP authentication	Configure a key and configure it as a trusted key	Authentication result
Yes	Yes	Yes	Yes	Yes	Succeeded. NTP messages can be sent and received correctly.
Yes	Yes	Yes	Yes	No	Failed. NTP messages cannot be sent and received correctly.
Yes	Yes	Yes	No	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	No	Yes	N/A	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	N/A	No	N/A	N/A	No authentication. NTP messages can be sent and received correctly.
No	N/A	N/A	N/A	N/A	No authentication. NTP messages can be sent and received correctly.

Configuring NTP authentication in symmetric active/passive mode

To ensure a successful NTP authentication, configure the same authentication key ID and key on the active peer and passive peer. Make sure the peer device is allowed to use the key ID for authentication on the local device.

To configure NTP authentication for an active peer:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.
5. Associate the specified key with a passive peer.	· Associate the specified key with a passive peer: ntp-service unicast-peer { ip-address \| peer-name } authentication-keyid keyid · Associate the specified key with a passive peer: ntp-service ipv6 unicast-peer { ipv6-address \| peer-name } authentication-keyid keyid	By default, a trusted key is not associated with a passive peer..

To configure NTP authentication for a passive peer:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.

NTP authentication results differ when different configurations are performed on active peer and passive peer. For more information, see Table 3. (N/A in the table means that whether the configuration is performed does not make any difference.)

Table 3 NTP authentication results

Active peer						Passive peer			Authentication result
Enable NTP authentication		Configure a key and configure it as a trusted key		Associate the key with a passive peer		Enable NTP authentication		Configure a key and configure it as a trusted key	Authentication result
Stratum level of the active and passive peers is not considered.
Yes	Yes		Yes		Yes		Yes		Succeeded. NTP messages can be sent and received correctly.
Yes	Yes		Yes		Yes		No		Failed. NTP messages cannot be sent and received correctly.
Yes	Yes		Yes		No		N/A		Failed. NTP messages cannot be sent and received correctly.
Yes	N/A		No		Yes		N/A		Failed. NTP messages cannot be sent and received correctly.
Yes	N/A		No		No		N/A		No authentication. NTP messages can be sent and received correctly.
No	N/A		N/A		Yes		N/A		Failed. NTP messages cannot be sent and received correctly.
No	N/A		N/A		No		N/A		No authentication. NTP messages can be sent and received correctly.
The active peer has a higher stratum than the passive peer.
Yes	No		Yes		N/A		N/A		Failed. NTP messages cannot be sent and received correctly.
The passive peer has a higher stratum than the active peer.
Yes	No		Yes		Yes		N/A		Failed. NTP messages cannot be sent and received correctly.
Yes	No		Yes		No		N/A		No authentication. NTP messages can be sent and received correctly.

Configuring NTP authentication in broadcast mode

To ensure a successful NTP authentication, configure the same authentication key ID and key on the broadcast server and client. Make sure the peer device is allowed to use the key ID for authentication on the local device.

To configure NTP authentication for a broadcast client:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.

To configure NTP authentication for a broadcast server:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.
5. Enter interface view.	interface interface-type interface-number	N/A
6. Associate the specified key with the broadcast server.	ntp-service broadcast-server authentication-keyid keyid	By default, the broadcast server is not associated with any key.

NTP authentication results differ when different configurations are performed on broadcast client and server. For more information, see Table 4. (N/A in the table means that whether the configuration is performed does not make any difference.)

Table 4 NTP authentication results

Broadcast server			Broadcast client		Authentication result
Enable NTP authentication	Configure a key and configure it as a trusted key	Associate the key with a broadcast server	Enable NTP authentication	Configure a key and configure it as a trusted key	Authentication result
Yes	Yes	Yes	Yes	Yes	Succeeded. NTP messages can be sent and received correctly.
Yes	Yes	Yes	Yes	No	Failed. NTP messages cannot be sent and received correctly.
Yes	Yes	Yes	No	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	No	Yes	Yes	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	No	Yes	No	N/A	No authentication. NTP messages can be sent and received correctly.
Yes	N/A	No	Yes	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	N/A	No	No	N/A	No authentication. NTP messages can be sent and received correctly.
No	N/A	N/A	Yes	N/A	Failed. NTP messages cannot be sent and received correctly.
No	N/A	N/A	No	N/A	No authentication. NTP messages can be sent and received correctly.

Configuring NTP authentication in multicast mode

To ensure a successful NTP authentication, configure the same authentication key ID and key on the multicast server and client. Make sure the peer device is allowed to use the key ID for authentication on the local device.

To configure NTP authentication for a multicast client:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.

To configure NTP authentication for a multicast server:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable NTP authentication.	ntp-service authentication enable	By default, NTP authentication is disabled.
3. Configure an NTP authentication key.	ntp-service authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no NTP authentication key is configured.
4. Configure the key as a trusted key.	ntp-service reliable authentication-keyid keyid	By default, no authentication key is configured as a trusted key.
5. Enter interface view.	interface interface-type interface-number	N/A
6. Associate the specified key with the multicast server.	· Associate the specified key with a multicast server: ntp-service multicast-server [ ip-address ] authentication-keyid keyid · Associate the specified key with an IPv6 multicast server: ntp-service ipv6 multicast-server ipv6-multicast-address authentication-keyid keyid	By default, no multicast server is associated with the specified key.

NTP authentication results differ when different configurations are performed on broadcast client and server. For more information, see Table 5. (N/A in the table means that whether the configuration is performed does not make any difference.)

Table 5 NTP authentication results

Multicast server			Multicast client		Authentication result
Enable NTP authentication	Configure a key and configure it as a trusted key	Associate the key with a multicast server	Enable NTP authentication	Configure a key and configure it as a trusted key	Authentication result
Yes	Yes	Yes	Yes	Yes	Succeeded. NTP messages can be sent and received correctly.
Yes	Yes	Yes	Yes	No	Failed. NTP messages cannot be sent and received correctly.
Yes	Yes	Yes	No	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	No	Yes	Yes	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	No	Yes	No	N/A	No authentication. NTP messages can be sent and received correctly.
Yes	N/A	No	Yes	N/A	Failed. NTP messages cannot be sent and received correctly.
Yes	N/A	No	No	N/A	No authentication. NTP messages can be sent and received correctly.
No	N/A	N/A	Yes	N/A	Failed. NTP messages cannot be sent and received correctly.
No	N/A	N/A	No	N/A	No authentication. NTP messages can be sent and received correctly.

Configuring NTP optional parameters

The configuration tasks in this section are optional tasks. Configure them to improve NTP security, performance, or reliability.

Specifying the source interface for NTP messages

To prevent interface status changes from causing NTP communication failures, configure the device to use the IP address of an interface that is always up. For example, you can configure the device to use a loopback interface as the source IP address for the NTP messages to be sent.

When the device responds to an NTP request, the source IP address of the NTP response is always the IP address of the interface that has received the NTP request.

Follow these guidelines when you specify the source interface for NTP messages:

· If you have specified the source interface for NTP messages in the ntp-service [ ipv6 ] unicast-server or ntp-service [ ipv6 ] unicast-peer command, the interface specified in the ntp-service [ ipv6 ] unicast-server or ntp-service [ ipv6 ] unicast-peer command works as the source interface for NTP messages.

· If you have configured the ntp-service broadcast-server or ntp-service [ ipv6 ] multicast-server command, the source interface for the broadcast or multicast NTP messages is the interface configured with the respective command.

To specify the source interface for NTP messages:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Specify the source interface for NTP messages.	· Specify the source interface for NTP messages: ntp-service source interface-type interface-number · Specify the source interface for IPv6 NTP messages: ntp-service ipv6 source interface-type interface-number	By default, no source interface is specified for NTP messages.

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Specify the source interface for NTP messages.

· Specify the source interface for NTP messages:
ntp-service source interface-type interface-number

· Specify the source interface for IPv6 NTP messages:
ntp-service ipv6 source interface-type interface-number

By default, no source interface is specified for NTP messages.

Disabling an interface from processing NTP messages

When NTP is enabled, all interfaces by default can process NTP messages. For security purposes, you can disable some of the interfaces from processing NTP messages.

To disable an interface from processing NTP messages:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Disable the interface from processing NTP messages.	· For IPv4: undo ntp-service inbound enable · For IPv6: undo ntp-service ipv6 inbound enable	By default, an interface processes NTP messages.

Configuring the maximum number of dynamic associations

NTP has the following types of associations:

· Static association—A manually created association.

· Dynamic association—Temporary association created by the system during NTP operation. A dynamic association is removed if no messages are exchanged within about 12 minutes.

The following describes how an association is established in different association modes:

· Client/server mode—After you specify an NTP server, the system creates a static association on the client. The server simply responds passively upon the receipt of a message, rather than creating an association (static or dynamic).

· Symmetric active/passive mode—After you specify a symmetric-passive peer on a symmetric active peer, static associations are created on the symmetric-active peer, and dynamic associations are created on the symmetric-passive peer.

· Broadcast or multicast mode—Static associations are created on the server, and dynamic associations are created on the client.

A single device can have a maximum of 128 concurrent associations, including static associations and dynamic associations.

Perform this task to restrict the number of dynamic associations to prevent dynamic associations from occupying too many system resources.

To configure the maximum number of dynamic associations:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Configure the maximum number of dynamic sessions allowed to be established.	ntp-service max-dynamic-sessions number	By default, the command can establish up to 100 dynamic sessions.

Setting a DSCP value for NTP packets

The DSCP value determines the sending precedence of a packet.

To set a DSCP value for NTP packets:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Set a DSCP value for NTP packets.	· IPv4 packets: ntp-service dscp dscp-value · IPv6 packets: ntp-service ipv6 dscp dscp-value	The default DSCP value: · IPv4 packets—48. · IPv6 packets—56.

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Set a DSCP value for NTP packets.

· IPv4 packets:
ntp-service dscp dscp-value

· IPv6 packets:
ntp-service ipv6 dscp dscp-value

The default DSCP value:

· IPv4 packets—48.

· IPv6 packets—56.

Configuring the local clock as a reference source

Follow these guidelines when you configure the local clock as a reference source:

· Make sure the local clock can provide the time accuracy required for the network. After you configure the local clock as a reference source, the local clock is synchronized, and can operate as a time server to synchronize other devices in the network. If the local clock is incorrect, timing errors occur.

· Before you configure this feature, adjust the local system time to make sure it is accurate.

· Devices differ in clock precision. To avoid network flapping and clock synchronization failure, do not configure multiple reference sources on the same network segment.

To configure the local clock as a reference source:

Step	Command	Remarks
3. Enter system view.	system-view	N/A
4. Configure the local clock as a reference source.	ntp-service refclock-master [ ip-address ] [ stratum ]	By default, the device does not use the local clock as a reference source.

Displaying and maintaining NTP

Execute display commands in any view.

Task	Command
Display information about IPv6 NTP associations.	display ntp-service ipv6 sessions [ verbose ]
Display information about IPv4 NTP associations.	display ntp-service sessions [ verbose ]
Display information about NTP service status.	display ntp-service status
Display brief information about the NTP servers from the local device back to the primary reference source.	display ntp-service trace [ source interface-type interface-number ]

NTP configuration examples

NTP client/server mode configuration example

Network requirements

As shown in Figure 4:

· Configure the local clock of the AC as a reference source, with the stratum level 2.

· Configure the switch to operate in client mode and specify the AC as the NTP server for the switch.

Figure 4 Network diagram

Configuration procedure

1. Assign an IP address to each interface, and make sure the AC and the switch can reach each other, as shown in Figure 4. (Details not shown.)

2. Configure the AC:

# Enable the NTP service.

<AC> system-view

[AC] ntp-service enable

# Specify the local clock as the reference source, with the stratum level 2.

[AC] ntp-service refclock-master 2

3. Configure the switch:

# Enable the NTP service.

<Switch> system-view

[Switch] ntp-service enable

# Specify the AC as the NTP server of the switch so that the switch is synchronized to the AC.

[Switch] ntp-service unicast-server 1.0.1.11

4. Verify the configuration:

# Verify that the switch has synchronized to the AC, and the clock stratum level is 3 on the switch.

[Switch] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 1.0.1.11

Local mode: client

Reference clock ID: 1.0.1.11

Leap indicator: 00

Clock jitter: 0.000977 s

Stability: 0.000 pps

Clock precision: 2^-10

Root delay: 0.00383 ms

Root dispersion: 16.26572 ms

Reference time: d0c6033f.b9923965 Wed, Dec 29 2010 18:58:07.724

# Verify that an IPv4 NTP association has been established between the switch and the AC.

[Switch] display ntp-service sessions

source reference stra reach poll now offset delay disper

********************************************************************************

[12345]1.0.1.11 127.127.1.0 2 1 64 15 -4.0 0.0038 16.262

Notes: 1 source(master), 2 source(peer), 3 selected, 4 candidate, 5 configured.

Total sessions: 1

IPv6 NTP client/server mode configuration example

Network requirements

As shown in Figure 5:

· Configure the local clock of the AC as a reference source, with the stratum level 2.

· Configure the switch to operate in client mode and specify the AC as the IPv6 NTP server for the switch.

Figure 5 Network diagram

Configuration procedure

1. Assign an IP address to each interface, and make sure the AC and the switch can reach each other, as shown in Figure 5. (Details not shown.)

2. Configure the AC:

# Enable the NTP service.

<AC> system-view

[AC] ntp-service enable

# Specify the local clock as the reference source, with the stratum level 2.

[AC] ntp-service refclock-master 2

3. Configure the switch:

# Enable the NTP service.

<Switch> system-view

[Switch] ntp-service enable

# Specify the AC as the IPv6 NTP server of the switch so that the switch is synchronized to the AC.

[Switch] ntp-service ipv6 unicast-server 3000::34

4. Verify the configuration:

# Verify that the switch has synchronized to the AC, and the clock stratum level is 3 on the switch.

[Switch] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 3000::34

Local mode: client

Reference clock ID: 163.29.247.19

Leap indicator: 00

Clock jitter: 0.000977 s

Stability: 0.000 pps

Clock precision: 2^-10

Root delay: 0.02649 ms

Root dispersion: 12.24641 ms

Reference time: d0c60419.9952fb3e Wed, Dec 29 2010 19:01:45.598

# Verify that an IPv6 NTP association has been established between the switch and the AC.

[Switch] display ntp-service ipv6 sessions

Notes: 1 source(master), 2 source(peer), 3 selected, 4 candidate, 5 configured.

Source: [12345]3000::34

Reference: 127.127.1.0 Clock stratum: 2

Reachabilities: 15 Poll interval: 64

Last receive time: 19 Offset: 0.0

Roundtrip delay: 0.0 Dispersion: 0.0

Total sessions: 1

NTP symmetric active/passive mode configuration example

Network requirements

As shown in Figure 6:

· Configure the local clock of the AC as a reference source, with the stratum level 2.

· Configure the AC to operate in symmetric-active mode and specify the switch as the passive peer of the AC.

Figure 6 Network diagram

Configuration procedure

1. Assign an IP address to each interface, and make sure the AC and the switch can reach each other, as shown in Figure 6. (Details not shown.)

2. Configure the switch:

# Enable the NTP service.

<Switch> system-view

[Switch] ntp-service enable

3. Configure the AC:

# Enable the NTP service.

<AC> system-view

[AC] ntp-service enable

# Specify the local clock as the reference source, with the stratum level 2.

[AC] ntp-service refclock-master 2

# Configure the switch as a symmetric passive peer.

[AC] ntp-service unicast-peer 3.0.1.32

4. Verify the configuration:

# Verify that the switch has synchronized to the AC and the clock stratum level is 3 on the switch.

[Switch] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 3.0.1.31

Local mode: sym_passive

Reference clock ID: 3.0.1.31

Leap indicator: 00

Clock jitter: 0.000916 s

Stability: 0.000 pps

Clock precision: 2^-17

Root delay: 0.00609 ms

Root dispersion: 1.95859 ms

Reference time: 83aec681.deb6d3e5 Wed, Jan 8 2014 14:33:11.081

# Verify that an IPv4 NTP association has been established between the switch and the AC.

[Switch] display ntp-service sessions

source reference stra reach poll now offset delay disper

********************************************************************************

[12]3.0.1.31 127.127.1.0 2 62 64 34 0.4251 6.0882 1392.1

Notes: 1 source(master), 2 source(peer), 3 selected, 4 candidate, 5 configured.

Total sessions: 1

IPv6 NTP symmetric active/passive mode configuration example

Network requirements

As shown in Figure 7:

· Configure the local clock of the AC as a reference source, with the stratum level 2.

· Configure the AC to operate in symmetric-active mode and specify the switch as the IPv6 passive peer of the AC.

Figure 7 Network diagram

Configuration procedure

1. Assign an IP address to each interface, and make sure the AC and the switch can reach each other, as shown in Figure 7. (Details not shown.)

2. Configure the switch:

# Enable the NTP service.

<Switch> system-view

[Switch] ntp-service enable

3. Configure the AC:

# Enable the NTP service.

<AC> system-view

[AC] ntp-service enable

# Specify the local clock as the reference source, with the stratum level 2.

[AC] ntp-service refclock-master 2

# Configure the switch as an IPv6 symmetric passive peer.

[AC] ntp-service ipv6 unicast-peer 3000::36

4. Verify the configuration:

# Verify that the switch has synchronized to the AC and the clock stratum level is 3 on the switch.

[Switch] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 3000::35

Local mode: sym_passive

Reference clock ID: 251.73.79.32

Leap indicator: 11

Clock jitter: 0.000977 s

Stability: 0.000 pps

Clock precision: 2^-10

Root delay: 0.01855 ms

Root dispersion: 9.23483 ms

Reference time: d0c6047c.97199f9f Wed, Dec 29 2010 19:03:24.590

# Verify that an IPv6 NTP association has been established between the switch and the AC.

[Switch] display ntp-service ipv6 sessions

Notes: 1 source(master), 2 source(peer), 3 selected, 4 candidate, 5 configured.

Source: [1234]3000::35

Reference: 127.127.1.0 Clock stratum: 2

Reachabilities: 15 Poll interval: 64

Last receive time: 19 Offset: 0.0

Roundtrip delay: 0.0 Dispersion: 0.0

Total sessions: 1

Configuration example for NTP authentication in client/server mode

Network requirements

As shown in Figure 8:

· Configure the local clock of the AC as a reference source, with the stratum level 2.

· Configure the switch to operate in client mode and specify the AC as the NTP server of the switch.

· Configure NTP authentication on both the AC and the switch.

Figure 8 Network diagram

Configuration procedure

1. Assign an IP address to each interface, and make sure the AC and the switch can reach each other, as shown in Figure 8. (Details not shown.)

2. Configure the AC:

# Enable the NTP service.

<AC> system-view

[AC] ntp-service enable

# Specify the local clock as the reference source, with the stratum level 2.

[AC] ntp-service refclock-master 2

3. Configure the switch:

# Enable the NTP service.

<Switch> system-view

[Switch] ntp-service enable

# Enable NTP authentication on the switch.

[Switch] ntp-service authentication enable

# Set an authentication key, and input the key in plain text.

[Switch] ntp-service authentication-keyid 42 authentication-mode md5 simple aNiceKey

# Specify the key as a trusted key.

[Switch] ntp-service reliable authentication-keyid 42

# Specify the AC as the NTP server of the switch, and associate the server with key 42.

[Switch] ntp-service unicast-server 1.0.1.11 authentication-keyid 42

Before the switch can synchronize its clock to that of the AC, enable NTP authentication for the AC.

4. Configure NTP authentication on the AC:

# Enable NTP authentication.

[AC] ntp-service authentication enable

# Set an authentication key, and input the key in plain text.

[AC] ntp-service authentication-keyid 42 authentication-mode md5 simple aNiceKey

# Specify the key as a trusted key.

[AC] ntp-service reliable authentication-keyid 42

5. Verify the configuration:

# Verify that the switch has synchronized to the AC, and the clock stratum level is 3 on the switch.

[Switch] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 1.0.1.11

Local mode: client

Reference clock ID: 1.0.1.11

Leap indicator: 00

Clock jitter: 0.005096 s

Stability: 0.000 pps

Clock precision: 2^-10

Root delay: 0.00655 ms

Root dispersion: 1.15869 ms

Reference time: d0c62687.ab1bba7d Wed, Dec 29 2010 21:28:39.668

# Verify that an IPv4 NTP association has been established between the switch and the AC.

[Switch] display ntp-service sessions

source reference stra reach poll now offset delay disper

********************************************************************************

[1245]1.0.1.11 127.127.1.0 2 1 64 519 -0.0 0.0065 0.0

Notes: 1 source(master),2 source(peer),3 selected,4 candidate,5 configured.

Total sessions: 1

Configuring SNTP

SNTP is a simplified, client-only version of NTP specified in RFC 4330. SNTP supports only the client/server mode. An SNTP-enabled device can receive time from NTP servers, but cannot provide time services to other devices.

SNTP uses the same packet format and packet exchange procedure as NTP, but provides faster synchronization at the price of time accuracy.

If you specify multiple NTP servers for an SNTP client, the server with the best stratum is selected. If multiple servers are at the same stratum, the NTP server whose time packet is first received is selected.

Configuration restrictions and guidelines

You cannot configure both NTP and SNTP on the same device.

Configuration task list

Tasks at a glance
(Required.) Enabling the SNTP service
(Required.) Specifying an NTP server for the device
(Optional.) Configuring SNTP authentication

Enabling the SNTP service

The NTP service and SNTP service are mutually exclusive. You can only enable either NTP service or SNTP service at a time.

To enable the SNTP service:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable the SNTP service.	sntp enable	By default, the SNTP service is not enabled.

Specifying an NTP server for the device

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Specify an NTP server for the device.	· For IPv4: sntp unicast-server { server-name \| ip-address } [ authentication-keyid keyid \| source interface-type interface-number \| version number ] * · For IPv6: sntp ipv6 unicast-server { server-name \| ipv6-address } [ authentication-keyid keyid \| source interface-type interface-number ] *	By default, no NTP server is specified for the device. Repeat this step to specify multiple NTP servers. To use authentication, you must specify the authentication-keyid keyid option.

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Specify an NTP server for the device.

· For IPv4:
sntp unicast-server { server-name | ip-address } [ authentication-keyid keyid | source interface-type interface-number | version number ] *

· For IPv6:
sntp ipv6 unicast-server { server-name | ipv6-address } [ authentication-keyid keyid | source interface-type interface-number ] *

By default, no NTP server is specified for the device.

Repeat this step to specify multiple NTP servers.

To use authentication, you must specify the authentication-keyid keyid option.

To use an NTP server as the time source, make sure its clock has been synchronized. If the stratum level of the NTP server is greater than or equal to that of the client, the client does not synchronize with the NTP server.

Configuring SNTP authentication

SNTP authentication makes sure an SNTP client is synchronized only to an authenticated trustworthy NTP server.

Follow these guidelines when you configure SNTP authentication:

· Enable authentication on both the NTP server and the SNTP client.

· Use the same authentication key ID and key on the NTP server and SNTP client. Specify the key as a trusted key on both the NTP server and the SNTP client. For information about configuring NTP authentication on an NTP server, see "Configuring NTP."

· On the SNTP client, associate the specified key with the NTP server. Make sure the server is allowed to use the key ID for authentication on the client.

With authentication disabled, the SNTP client can synchronize with the NTP server regardless of whether the NTP server is enabled with authentication.

To configure SNTP authentication on the SNTP client:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable SNTP authentication.	sntp authentication enable	By default, SNTP authentication is disabled.
3. Configure an SNTP authentication key.	sntp authentication-keyid keyid authentication-mode md5 { cipher \| simple } string [ acl ipv4-acl-number \| ipv6 acl ipv6-acl-number ] *	By default, no SNTP authentication key is configured.
4. Specify the key as a trusted key.	sntp reliable authentication-keyid keyid	By default, no trusted key is specified.
5. Associate the SNTP authentication key with an NTP server.	· For IPv4: sntp unicast-server { server-name \| ip-address } authentication-keyid keyid · For IPv6: sntp ipv6 unicast-server { server-name \| ipv6-address } authentication-keyid keyid	By default, no NTP server is specified.

Displaying and maintaining SNTP

Execute display commands in any view.

Task	Command
Display information about all IPv6 SNTP associations.	display sntp ipv6 sessions
Display information about all IPv4 SNTP associations.	display sntp sessions

SNTP configuration example

Network requirements

As shown in Figure 9:

· Configure the local clock of the AC as a reference source, with the stratum level 2.

· Configure the switch to operate in SNTP client mode, and specify the AC as the NTP server.

· Configure NTP authentication on the AC and SNTP authentication on the switch.

Figure 9 Network diagram

Configuration procedure

1. Assign an IP address to each interface, and make sure the AC and the switch can reach each other, as shown in Figure 9. (Details not shown.)

2. Configure the AC:

# Enable the NTP service.

<AC> system-view

[AC] ntp-service enable

# Configure the local clock of the AC as a reference source, with the stratum level 2.

[AC] ntp-service refclock-master 2

# Enable NTP authentication on the AC.

[AC] ntp-service authentication enable

# Configure an NTP authentication key, with the key ID of 10 and key value of aNiceKey. Input the key in plain text.

[AC] ntp-service authentication-keyid 10 authentication-mode md5 simple aNiceKey

# Specify the key as a trusted key.

[AC] ntp-service reliable authentication-keyid 10

3. Configure the switch:

# Enable the SNTP service.

<Switch> system-view

[Switch] sntp enable

# Enable SNTP authentication on the switch.

[Switch] sntp authentication enable

# Configure an SNTP authentication key, with the key ID of 10 and key value of aNiceKey. Input the key in plain text.

[Switch] sntp authentication-keyid 10 authentication-mode md5 simple aNiceKey

# Specify the key as a trusted key.

[Switch] sntp reliable authentication-keyid 10

# Specify the AC as the NTP server of the switch, and associate the server with key 10.

[Switch] sntp unicast-server 1.0.1.11 authentication-keyid 10

4. Verify the configuration:

# Verify that an SNTP association has been established between the switch and the AC, and the switch has synchronized to the AC.

[Switch] display sntp sessions

NTP server Stratum Version Last receive time

1.0.1.11 2 4 Tue, May 17 2011 9:11:20.833 (Synced)

12-Network Management and Monitoring

Overview

NTP architecture

NTP access control

NTP authentication

Configuration restrictions and guidelines

Configuring a broadcast client

Configuring the broadcast server

Configuring a multicast client

Configuring the multicast server

Configuring access control rights

Configuring NTP authentication

Configuring NTP optional parameters

Configuring the maximum number of dynamic associations

Displaying and maintaining NTP

NTP configuration examples

NTP client/server mode configuration example

Network requirements

Configuration procedure

Network requirements

Configuration procedure

NTP symmetric active/passive mode configuration example

Network requirements

Configuration procedure

Network requirements

Configuration procedure

Network requirements

Configuration procedure

Specifying an NTP server for the device

Displaying and maintaining SNTP

SNTP configuration example

Network requirements

Configuration procedure

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