Various tasks, including network management, charging, auditing, and distributed computing depend on accurate and synchronized system time setting on the network devices. NTP is typically used in large networks to dynamically synchronize time among network devices.

NTP guarantees higher clock accuracy than manual system clock setting and relieves administrators from massive workload of settings device clocks one by one.

NTP working mechanism

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

Figure 1 Basic work flow

The synchronization process is as follows:

1. Device A sends to Device B an NTP request message, which is timestamped T1 when it leaves Device A.

2. Device B replies with an NTP response message, which carries:

¡ Timestamp T1.

¡ Timestamp T2 when the NTP request message arrived at Device B.

¡ Timestamp T2 when the NTP response message was sent from Device B.

3. Upon receiving the NTP response message, Device A records timestamp T4. Device A then get four timestamps T1, T2, T3, and T4 and can calculate the following parameters based on the timestamps:

¡ Roundtrip delay of the NTP message: Delay = (T4 – T1) – (T3 – T2).

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

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

CAUTION:

When the device acts as an NTP client, the NTP server's clock stratum must be not smaller than 0 and not larger than 14. If the NTP server's clock stratum is larger than 14, the device will not synchronize with that server's clock. You can log in to the NTP server to change its clock stratum by executing the ntp-service refclock-master command.

· To check the stratum for an IPv4 NTP server, execute the display ntp-service sessions command on the device and check the stra field in the output.

· To check the stratum for an IPv6 NTP server, execute the display ntp-service ipv6 sessions command on the device and check the Clock stratum field in the output.

NTP uses stratums 0 to 16 to define clock accuracy, as shown in Figure 2. A lower stratum value represents higher accuracy.

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.

NTP association modes

NTP supports the following association modes:

· Client/server mode

· Symmetric active/passive mode

· Broadcast mode

· Multicast mode

You can select one or more association modes for time synchronization. Table 1 provides detailed description for the four association 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, multicast servers, and broadcast servers.

Table 1 NTP association modes

Mode	Working process	Synchronization direction	Application scenario
Client/server	1. A client sends a clock synchronization request message to the NTP servers. 2. Upon receiving the message, the servers automatically operate in server mode and send a reply. 3. The client selects an optimal clock based on the received response messages and synchronizes its local clock to the optimal reference source.	From the server to the client	As Figure 2 shows, this mode is intended for for scenarios where devices with a higher stratum value obtain time from a device with a lower stratum value. You are required to specify the IP address of the NTP server on the client.
Symmetric active/passive	1. A symmetric active peer periodically sends a clock synchronization message to symmetric passive peers. 2. Upon receiving the message, the symmetric passive peers automatically operates in symmetric passive mode and send a reply. 3. The symmetric active peer selects an optimal clock based on the received response messages and synchronizes its local clock to the optimal reference source.	· If the symmetric peers are the same in the clock stratum, they can be synchronized to each other. · If the symmetric peers are different in the clock stratum, the peer with a smaller clock stratum will synchronize the clock of the peer with a greater clock 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. You are required to specify the IP address of the symmetric passive peer on the symmetric active peer.
Broadcast	1. A broadcast server periodically sends clock synchronization request messages to the broadcast address 255.255.255.255. 2. Broadcast clients listen to the broadcast messages from the server with synchronize to the server based on the broadcast messages. When a broadcast 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.	From the broadcast server to the 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 lower time accuracy than the client/server and symmetric active/passive modes because only the broadcast servers send clock synchronization messages.
Multicast	1. A multicast server periodically sends clock synchronization request messages to the user-configured multicast address. 2. Clients listen to the multicast messages from servers and synchronize to the server according to the received messages. When a client receives the first multicast message, the client and the server start to exchange messages to calculate the network delay between them. Then, only the multicast server sends clock synchronization messages.	From the multicast server to the client.	A multicast server can provide time synchronization for clients in the same subnet or in different subnets. The multicast mode has lower time accuracy than the client/server and symmetric active/passive modes.

NTP security

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

NTP access control

You can control NTP access by using an ACL. The access rights are in the following order, from the least restrictive to the 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 acts as a client, specify the peer access right for it so that it can synchronize its time to a time server. When the device acts as a time server, specify the peer, server, or synchronization access right for it so that it can synchronize the time of its clients.

When the device receives an NTP request, it matches the request against the access rights in 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 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/HMAC authentication 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/HMAC authentication 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.

NTP for MPLS L3VPN instances

On an MPLS L3VPN network, a PE that acts as an NTP client or active peer can synchronize with the NTP server or passive peer in an MPLS L3VPN instance.

As shown in Figure 4, users in VPN 1 and VPN 2 are connected to the MPLS backbone network through provider edge (PE) devices. VPN instances vpn1 and vpn2 have been created for VPN 1 and VPN 2, respectively on the PEs. Services of the two VPN instances are isolated. Time synchronization between PEs and devices in the two VPN instances can be realized if you perform the following tasks:

· Configure the PEs to operate in NTP client or symmetric active mode.

· Specify the VPN instance to which the NTP server or NTP symmetric passive peer belongs.

For more information about MPLS L3VPN, VPN instance, and PE, see MPLS L3VPN configuration in MPLS Configuration Guide.

Figure 4 Network diagram

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IMPORTANT:

To synchronize the device time with devices in multiple MPLS L3VPN instances, you can configure NTP only in unicast mode rather than broadcast mode or multicast mode.

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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

Restrictions and guidelines: NTP configuration

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

· NTP is supported only on the following Layer 3 interfaces:

¡ Layer 3 Ethernet interfaces.

¡ Layer 3 Ethernet subinterfaces.

¡ Layer 3 aggregate interfaces.

¡ Layer 3 aggregate subinterfaces.

¡ VLAN interfaces.

¡ Tunnel interfaces.

· Do not configure NTP settings 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 avoid frequent time changes or even synchronization failures, do not specify more than one reference source on a network.

· For correct time synchronization, make sure the time offset between the system time and the NTP clock source is less than 68 years.

You must use the clock protocol command to specify NTP for obtaining the time. For more information about the clock protocol command, see device management commands in Fundamentals Command Reference.

CAUTION:

· To check the stratum for an IPv4 NTP server, execute the display ntp-service sessions command on the device and check the stra field in the output.

· To check the stratum for an IPv6 NTP server, execute the display ntp-service ipv6 sessions command on the device and check the Clock stratum field in the output.

NTP tasks at a glance

To configure NTP, perform the following tasks:

1. Enabling the NTP service

2. Configuring NTP association mode

¡ Configuring NTP in client/server mode

¡ Configuring NTP in symmetric active/passive mode

¡ Configuring NTP in broadcast mode

¡ Configuring NTP in multicast mode

3. (Optional.) Configuring the local clock as the reference source

4. (Optional.) Configuring access control rights

5. (Optional.) Configuring NTP authentication

¡ Configuring NTP authentication in client/server mode

¡ Configuring NTP authentication in symmetric active/passive mode

¡ Configuring NTP authentication in broadcast mode

¡ Configuring NTP authentication in multicast mode

6. (Optional.) Controlling NTP packet sending and receiving

¡ Specifying the source interface for NTP messages

¡ Disabling an interface from receiving NTP messages

¡ Configuring the maximum number of dynamic associations

¡ Setting a DSCP value for NTP packets

· (Optional.) Specifying the NTP time-offset thresholds for log and trap outputs

Enabling the NTP service

Restrictions and guidelines

NTP and SNTP are mutually exclusive. Before you enable NTP, make sure SNTP is disabled.

Procedure

1. Enter system view.

system-view

2. Enable the NTP service.

ntp-service enable

By default, the NTP service is disabled.

Configuring NTP association mode

Configuring NTP in client/server mode

Restrictions and guidelines

To configure NTP in client/server mode, specify an NTP server for the client.

For a client to synchronize to an NTP server, make sure the server is synchronized by other devices or uses its local clock as the reference source.

The stratum of an NTP server must be smaller than that of the client. If the stratum of a server is greater than or equal to a client, the client will not synchronize to that server.

You can specify multiple servers for a client by executing the ntp-service unicast-server or ntp-service ipv6 unicast-server command multiple times.

Configuring the NTP client

1. Enter system view.

system-view

2. Specify an NTP server for the device.

IPv4:

ntp-service unicast-server { server-name | ip-address } [ vpn-instance vpn-instance-name ] [ authentication-keyid keyid | priority | source interface-type interface-number | version number ] *

IPv6:

ntp-service ipv6 unicast-server { server-name | ipv6-address } [ vpn-instance vpn-instance-name ] [ authentication-keyid keyid | priority | source interface-type interface-number ] *

By default, no NTP server is specified.

Configuring the NTP server

1. Enter system view.

system-view

2. Enable NTP server.

IPv4 network:

ntp-service time-server enable

By default, NTP server is enabled.

IPv6 network:

ntp-service ipv6 time-server enable

By default, IPv6 NTP server is enabled.

A device can provide NTP time synchronization to other devices only when it meets the following conditions:

¡ NTP server is enabled on the device.

¡ The device is permitted by the ACLs configured in the ntp-service acl or ntp-service ipv6 acl command on the other devices.

If you disable NTP server on the device, the device cannot provide NTP time synchronization to other devices.

Configuring NTP in symmetric active/passive mode

Restrictions and guidelines

To configure NTP in symmetric active/passive mode, specify a symmetric passive peer for the active peer.

For a symmetric passive peer to process NTP messages from a symmetric active peer, execute the ntp-service enable command on the symmetric passive peer to enable NTP.

For time synchronization between the symmetric active peer and the symmetric passive peer, make sure either or both of them are in synchronized state.

You can specify multiple symmetric passive peers by executing the ntp-service unicast-peer or ntp-service ipv6 unicast-peer command multiple times.

Procedure

1. Enter system view.

system-view

2. Specify a symmetric passive peer for the device.

IPv4:

ntp-service unicast-peer { peer-name | ip-address } [ vpn-instance vpn-instance-name ] [ authentication-keyid keyid | priority | source interface-type interface-number | version number ] *

IPv6:

ntp-service ipv6 unicast-peer { peer-name | ipv6-address } [ vpn-instance vpn-instance-name ] [ authentication-keyid keyid | priority | source interface-type interface-number ] *

By default, no symmetric passive peer is specified.

3. Enable NTP server.

IPv4 network:

ntp-service time-server enable

By default, NTP server is enabled.

IPv6 network:

ntp-service ipv6 time-server enable

By default, IPv6 NTP server is enabled.

A device can provide NTP time synchronization to other devices only when it meets the following conditions:

¡ NTP server is enabled on the device.

¡ The device is permitted by the ACLs configured in the ntp-service acl or ntp-service ipv6 acl command on the other devices.

If you disable NTP server on the device, the device cannot provide NTP time synchronization to other devices.

Configuring NTP in broadcast mode

Restrictions and guidelines

To configure NTP in broadcast mode, you must configure an NTP broadcast client and an NTP broadcast server.

For a broadcast client to synchronize to a broadcast server, make sure the broadcast server is synchronized by other devices or uses its local clock as the reference source.

Configuring the broadcast client

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the device to operate in broadcast client mode.

ntp-service broadcast-client

By default, the device does not operate in any NTP association mode.

After you execute the command, the device receives NTP broadcast messages from the specified interface.

Configuring the broadcast server

1. Enter system view.

system-view

2. Enable NTP server.

IPv4 network:

ntp-service time-server enable

By default, NTP server is enabled.

IPv6 network:

ntp-service ipv6 time-server enable

By default, IPv6 NTP server is enabled.

A device can provide NTP time synchronization to other devices only when it meets the following conditions:

¡ NTP server is enabled on the device.

¡ The device is permitted by the ACLs configured in the ntp-service acl or ntp-service ipv6 acl command on the other devices.

If you disable NTP server on the device, the device cannot provide NTP time synchronization to other devices.

3. Enter interface view.

interface interface-type interface-number

4. 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 any NTP association mode.

After you execute the command, the device sends NTP broadcast messages from the specified interface.

Configuring NTP in multicast mode

Restrictions and guidelines

To configure NTP in multicast mode, you must configure an NTP multicast client and an NTP multicast server.

For a multicast client to synchronize to a multicast server, make sure the multicast server is synchronized by other devices or uses its local clock as the reference source.

Configuring a multicast client

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the device to operate in multicast client mode.

IPv4:

ntp-service multicast-client [ ip-address ]

IPv6:

ntp-service ipv6 multicast-client ipv6-address

By default, the device does not operate in any NTP association mode.

After you execute the command, the device receives NTP multicast messages from the specified interface.

Configuring the multicast server

1. Enter system view.

system-view

2. Enable NTP server.

IPv4 network:

ntp-service time-server enable

By default, NTP server is enabled.

IPv6 network:

ntp-service ipv6 time-server enable

By default, IPv6 NTP server is enabled.

A device can provide NTP time synchronization to other devices only when it meets the following conditions:

¡ NTP server is enabled on the device.

¡ The device is permitted by the ACLs configured in the ntp-service acl or ntp-service ipv6 acl command on the other devices.

If you disable NTP server on the device, the device cannot provide NTP time synchronization to other devices.

3. Enter interface view.

interface interface-type interface-number

4. Configure the device to operate in multicast server mode.

IPv4:

ntp-service multicast-server [ ip-address ] [ authentication-keyid keyid | ttl ttl-number | version number ] *

IPv6:

ntp-service ipv6 multicast-server ipv6-address [ authentication-keyid keyid | ttl ttl-number ] *

By default, the device does not operate in any NTP association mode.

After you execute the command, the device sends NTP multicast messages from the specified interface.

Configuring the local clock as the reference source

About this task

This task enables the device to use the local clock as the reference so that the device is synchronized.

Restrictions and guidelines

Make sure the local clock can provide the time accuracy required for the network. After you configure the local clock as the 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.

The system time reverts to the initial BIOS default after a cold reboot. As a best practice, do not configure the local clock as the reference source or configure the device as a time server.

Devices differ in clock precision. As a best practice to avoid network flapping and clock synchronization failure, configure only one reference clock on the same network segment and make sure the clock has high precision.

Prerequisites

Before you configure this feature, adjust the local system time to ensure that it is accurate.

Procedure

1. Enter system view.

system-view

2. Configure the local clock as the reference source.

ntp-service refclock-master [ ip-address ] [ stratum ]

By default, the device does not use the local clock as the reference source.

Configuring access control rights

Prerequisites

Before you configure the right for peer devices to access the NTP services on the local device, create and configure ACLs associated with the access right. For information about configuring an ACL, see ACL and QoS Configuration Guide.

Restrictions and guidelines

Follow the restrictions and guidelines as described in Table 2 to configure the NTP access control rights.

Table 2 Restrictions and guidelines for configuring NTP access control rights

NTP access control right	Whether the time can be synchronized (whether configurable on a client)	Whether can synchronize the time of other devices (whether configurable on a time server)	Whether control queries are allowed
Peer	Yes	Yes	Yes
Server	No	Yes	Yes
Synchronization	No	Yes	No
Query	No	No	Yes

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The ntp-service noquery enable command and its undo form are used only to configure the device to disallow or allow control queries and do not disable or enable clock synchronization. If the ntp-service noquery enable command or its undo form and the ntp-service acl or ntp-service ipv6 acl command are both configured, the ntp-service noquery enable command or its undo form determines whether control queries are allowed.

Procedure

1. Enter system view.

system-view

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

IPv4:

ntp-service { peer | query | server | synchronization } acl { ipv4-acl-number | name ipv4-acl-name }

IPv6:

ntp-service ipv6 { peer | query | server | synchronization } acl { ipv6-acl-number | name ipv6-acl-name }

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

3. Disallow control queries for the local device.

ntp-service noquery enable

By default, control queries for the local device are allowed.

Configuring NTP authentication

Configuring NTP authentication in client/server mode

Restrictions and guidelines

To ensure a successful NTP authentication in client/server mode, configure the same authentication key ID, algorithm, 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.

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

Table 3 NTP authentication results

Client			Server
Enable NTP authentication	Specify the server and key	Trusted key	Enable NTP authentication	Trusted key
Successful authentication
Yes	Yes	Yes	Yes	Yes
Failed authentication
Yes	Yes	Yes	Yes	No
Yes	Yes	Yes	No	N/A
Yes	Yes	No	N/A	N/A
Authentication not performed
Yes	No	N/A	N/A	N/A
No	N/A	N/A	N/A	N/A

Configuring NTP authentication for a client

1. Enter system view.

system-view

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 { hmac-sha-1 | hmac-sha-256 | hmac-sha-384 | hmac-sha-512 | md5 } { cipher | simple } string [ acl ipv4-acl-number | ipv6 acl ipv6-acl-number ] *

By default, no NTP authentication key exists.

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.

IPv4:

ntp-service unicast-server { server-name | ip-address } [ vpn-instance vpn-instance-name ] authentication-keyid keyid

IPv6:

ntp-service ipv6 unicast-server { server-name | ipv6-address } [ vpn-instance vpn-instance-name ] authentication-keyid keyid

Configuring NTP authentication for a server

1. Enter system view.

system-view

2. Enable NTP authentication.

ntp-service authentication enable

By default, NTP authentication is disabled.

3. Configure an NTP authentication key.

By default, no NTP authentication key exists.

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.

Configuring NTP authentication in symmetric active/passive mode

Restrictions and guidelines

To ensure a successful NTP authentication in symmetric active/passive mode, configure the same authentication key ID, algorithm, 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.

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

Table 4 NTP authentication results

Active peer				Passive peer
Enable NTP authentication	Specify the peer and key	Trusted key	Stratum level	Enable NTP authentication	Trusted key
Successful authentication
Yes	Yes	Yes	N/A	Yes	Yes
Failed authentication
Yes	Yes	Yes	N/A	Yes	No
Yes	Yes	Yes	N/A	No	N/A
Yes	No	N/A	N/A	Yes	N/A
No	N/A	N/A	N/A	Yes	N/A
Yes	Yes	No	Larger than the passive peer	N/A	N/A
Yes	Yes	No	Smaller than the passive peer	Yes	N/A
Authentication not performed
Yes	No	N/A	N/A	No	N/A
No	N/A	N/A	N/A	No	N/A
Yes	Yes	No	Smaller than the passive peer	No	N/A

Configuring NTP authentication for an active peer

1. Enter system view.

system-view

2. Enable NTP authentication.

ntp-service authentication enable

By default, NTP authentication is disabled.

3. Configure an NTP authentication key.

By default, no NTP authentication key exists.

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.

IPv4:

ntp-service unicast-peer { ip-address | peer-name } [ vpn-instance vpn-instance-name ] authentication-keyid keyid

IPv6:

ntp-service ipv6 unicast-peer { ipv6-address | peer-name } [ vpn-instance vpn-instance-name ] authentication-keyid keyid

Configuring NTP authentication for a passive peer

1. Enter system view.

system-view

2. Enable NTP authentication.

ntp-service authentication enable

By default, NTP authentication is disabled.

3. Configure an NTP authentication key.

By default, no NTP authentication key exists.

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.

Configuring NTP authentication in broadcast mode

Restrictions and guidelines

To ensure a successful NTP authentication in broadcast mode, configure the same authentication key ID, algorithm, 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.

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 or not does not make any difference.)

Table 5 NTP authentication results

Broadcast server			Broadcast client
Enable NTP authentication	Specify the server and key	Trusted key	Enable NTP authentication	Trusted key
Successful authentication
Yes	Yes	Yes	Yes	Yes
Failed authentication
Yes	Yes	Yes	Yes	No
Yes	Yes	Yes	No	N/A
Yes	Yes	No	Yes	N/A
Yes	No	N/A	Yes	N/A
No	N/A	N/A	Yes	N/A
Authentication not performed
Yes	Yes	No	No	N/A
Yes	No	N/A	No	N/A
No	N/A	N/A	No	N/A

Configuring NTP authentication for a broadcast client

1. Enter system view.

system-view

2. Enable NTP authentication.

ntp-service authentication enable

By default, NTP authentication is disabled.

3. Configure an NTP authentication key.

By default, no NTP authentication key exists.

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.

Configuring NTP authentication for a broadcast server

1. Enter system view.

system-view

2. Enable NTP authentication.

ntp-service authentication enable

By default, NTP authentication is disabled.

3. Configure an NTP authentication key.

By default, no NTP authentication key exists.

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

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 a key.

Configuring NTP authentication in multicast mode

Restrictions and guidelines

To ensure a successful NTP authentication in multicast mode, configure the same authentication key ID, algorithm, 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.

NTP authentication results differ when different configurations are performed on broadcast client and server. For more information, see Table 6. (N/A in the table means that whether the configuration is performed or not does not make any difference.)

Table 6 NTP authentication results

Multicast server			Multicast client
Enable NTP authentication	Specify the server and key	Trusted key	Enable NTP authentication	Trusted key
Successful authentication
Yes	Yes	Yes	Yes	Yes
Failed authentication
Yes	Yes	Yes	Yes	No
Yes	Yes	Yes	No	N/A
Yes	Yes	No	Yes	N/A
Yes	No	N/A	Yes	N/A
No	N/A	N/A	Yes	N/A
Authentication not performed
Yes	Yes	No	No	N/A
Yes	No	N/A	No	N/A
No	N/A	N/A	No	N/A

Configuring NTP authentication for a multicast client

1. Enter system view.

system-view

2. Enable NTP authentication.

ntp-service authentication enable

By default, NTP authentication is disabled.

3. Configure an NTP authentication key.

By default, no NTP authentication key exists.

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.

Configuring NTP authentication for a multicast server

1. Enter system view.

system-view

2. Enable NTP authentication.

ntp-service authentication enable

By default, NTP authentication is disabled.

3. Configure an NTP authentication key.

By default, no NTP authentication key exists.

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

6. Associate the specified key with a multicast server.

IPv4:

ntp-service multicast-server [ ip-address ] authentication-keyid keyid

IPv6:

ntp-service ipv6 multicast-server ipv6-multicast-address authentication-keyid keyid

By default, no multicast server is associated with the specified key.

Controlling NTP packet sending and receiving

Specifying the source interface for NTP messages

Restrictions and guidelines

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.

If you have specified the source interface for NTP messages in the ntp-service unicast-server/ntp-service ipv6 unicast-server or ntp-service unicast-peer/ntp-service ipv6 unicast-peer command, the specified interface is the source interface for NTP messages.

If you have configured the ntp-service broadcast-server or ntp-service multicast-server/ntp-service ipv6 multicast-server command in an interface view, this interface acts as the source interface for broadcast or multicast NTP messages.

Procedure

1. Enter system view.

system-view

2. Specify the source interface for NTP packets.

IPv4:

ntp-service source interface-type interface-number

IPv6:

ntp-service ipv6 source interface-type interface-number

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

Disabling an interface from receiving NTP messages

About this task

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

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Disable the interface from receiving NTP packets.

IPv4:

undo ntp-service inbound enable

IPv6:

undo ntp-service ipv6 inbound enable

By default, an interface receives NTP messages.

Configuring the maximum number of dynamic associations

About this task

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

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.

Restrictions and guidelines

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

The ntp-service max-dynamic-sessions command does not affect existing NTP associations. After this command is configured, new associations will not be established if the maximum number of associations has been reached or exceeded.

Procedure

1. Enter system view.

system-view

2. Configure the maximum number of dynamic sessions.

ntp-service max-dynamic-sessions number

By default, the maximum number of dynamic sessions is 100.

Setting a DSCP value for NTP packets

About this task

The DSCP value determines the sending precedence of an NTP packet.

Procedure

1. Enter system view.

system-view

2. Set a DSCP value for NTP packets.

IPv4:

ntp-service dscp dscp-value

IPv6:

ntp-service ipv6 dscp dscp-value

The default DSCP value is 48 for IPv4 packets and 56 for IPv6 packets.

Specifying the NTP time-offset thresholds for log and trap outputs

About this task

By default, the NTP client synchronizes the time with the server and outputs a log and a trap when the time offset between the client and server exceeds 128 ms for multiple times.

After you set the NTP time-offset thresholds for log and trap outputs, the NTP client synchronizes the time with the server when the time offset exceeds 128 ms for multiple times, but outputs a log or trap only when the time offset exceeds the specified threshold.

Procedure

1. Enter system view.

system-view

2. Specify the NTP time-offset thresholds for log and trap outputs.

ntp-service time-offset-threshold { log log-threshold | trap trap-threshold } *

By default, no NTP time-offset thresholds are set for log and trap outputs.

Display and maintenance commands for NTP

The ntp-service noquery enable command is mutually exclusive with the display ntp-service trace command. To use the display ntp-service trace command, you must configure the device to allow control queries.

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 NTP server.	display ntp-service trace [ source interface-type interface-number ]

‌

NTP configuration examples

Example: Configuring NTP client/server association mode

Network configuration

As shown in Figure 5, perform the following tasks:

· Configure Device A's local clock as its reference source, with stratum level 2.

· Configure Device B to operate in client mode and specify Device A as the NTP server of Device B.

Figure 5 Network diagram

‌

Procedure

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

2. Configure Device A:

# Enable the NTP service.

<DeviceA> system-view

[DeviceA] ntp-service enable

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

[DeviceA] ntp-service refclock-master 2

3. Configure Device B:

# Enable the NTP service.

<DeviceB> system-view

[DeviceB] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceB] clock protocol ntp

# Specify Device A as the NTP server of Device B.

[DeviceB] ntp-service unicast-server 1.0.1.11

Verifying the configuration

# Verify that Device B has synchronized its time with Device A, and the clock stratum level of Device B is 3.

[DeviceB] 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^-18

Root delay: 0.00383 ms

Root dispersion: 16.26572 ms

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

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between Device B and Device A.

[DeviceB] 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

Example: Configuring IPv6 NTP client/server association mode

Network configuration

As shown in Figure 6, perform the following tasks:

· Configure Device A's local clock as its reference source, with stratum level 2.

· Configure Device B to operate in client mode and specify Device A as the IPv6 NTP server of Device B.

Figure 6 Network diagram

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Procedure

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

2. Configure Device A:

# Enable the NTP service.

<DeviceA> system-view

[DeviceA] ntp-service enable

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

[DeviceA] ntp-service refclock-master 2

3. Configure Device B:

# Enable the NTP service.

<DeviceB> system-view

[DeviceB] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceB] clock protocol ntp

# Specify Device A as the IPv6 NTP server of Device B.

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

Verifying the configuration

# Verify that Device B has synchronized its time with Device A, and the clock stratum level of Device B is 3.

[DeviceB] 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^-18

Root delay: 0.02649 ms

Root dispersion: 12.24641 ms

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

Sync state from NTP server to local clock: clock synced

# Verify that an IPv6 NTP association has been established between Device B and Device A.

[DeviceB] 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

Example: Configuring NTP symmetric active/passive association mode

Network configuration

As shown in Figure 7, perform the following tasks:

· Configure Device A's local clock as its reference source, with stratum level 2.

· Configure Device A to operate in symmetric active mode and specify Device B as the passive peer of Device A.

Figure 7 Network diagram

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Procedure

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

2. Configure Device B:

# Enable the NTP service.

<DeviceB> system-view

[DeviceA] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceB] clock protocol ntp

3. Configure Device A:

# Enable the NTP service.

<DeviceA> system-view

[DeviceB] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceA] clock protocol ntp

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

[DeviceA] ntp-service refclock-master 2

# Configure Device B as its symmetric passive peer.

[DeviceA] ntp-service unicast-peer 3.0.1.32

Verifying the configuration

# Verify that Device B has synchronized its time with Device A.

[DeviceB] 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

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between Device B and Device A.

[DeviceB] 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

Example: Configuring IPv6 NTP symmetric active/passive association mode

Network configuration

As shown in Figure 8, perform the following tasks:

· Configure Device A's local clock as its reference source, with stratum level 2.

· Configure Device A to operate in symmetric active mode and specify Device B as the IPv6 passive peer of Device A.

Figure 8 Network diagram

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Procedure

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

2. Configure Device B:

# Enable the NTP service.

<DeviceB> system-view

[DeviceB] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceB] clock protocol ntp

3. Configure Device A:

# Enable the NTP service.

<DeviceA> system-view

[DeviceA] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceA] clock protocol ntp

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

[DeviceA] ntp-service refclock-master 2

# Configure Device B as the IPv6 symmetric passive peer.

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

Verifying the configuration

# Verify that Device B has synchronized its time with Device A.

[DeviceB] 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

Sync state from NTP server to local clock: clock synced

# Verify that an IPv6 NTP association has been established between Device B and Device A.

[DeviceB] 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

Example: Configuring NTP authentication in client/server association mode

Network configuration

As shown in Figure 9, perform the following tasks:

· Configure Device A's local clock as its reference source, with stratum level 2.

· Configure Device B to operate in client mode and specify Device A as the NTP server of Device B.

· Configure NTP authentication on both Device A and Device B.

Figure 9 Network diagram

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Procedure

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

2. Configure Device A:

# Enable the NTP service.

<DeviceA> system-view

[DeviceA] ntp-service enable

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

[DeviceA] ntp-service refclock-master 2

3. Configure Device B:

# Enable the NTP service.

<DeviceB> system-view

[DeviceB] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceB] clock protocol ntp

# Enable NTP authentication on Device B.

[DeviceB] ntp-service authentication enable

# Create a plaintext authentication key, with key ID 42 and key value aNiceKey.

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

# Specify the key as a trusted key.

[DeviceB] ntp-service reliable authentication-keyid 42

# Specify Device A as the NTP server of Device B, and associate the server with key 42.

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

To enable Device B to synchronize its clock with Device A, enable NTP authentication on Device A.

4. Configure NTP authentication on Device A:

# Enable NTP authentication.

[DeviceA] ntp-service authentication enable

# Create a plaintext authentication key, with key ID 42 and key value aNiceKey.

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

# Specify the key as a trusted key.

[DeviceA] ntp-service reliable authentication-keyid 42

Verifying the configuration

# Verify that Device B has synchronized its time with Device A, and the clock stratum level of Device B is 3.

[DeviceB] 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

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between Device B and Device A.

[DeviceB] 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

Example: Configuring NTP broadcast association mode

Network configuration

As shown in Figure 10, configure Router C as the NTP server of multiple devices on the same network segment so that these devices synchronize the time with Router C.

· Configure Router C's local clock as its reference source, with stratum level 2.

· Configure Router C to operate in broadcast server mode and send broadcast messages from Ten-GigabitEthernet 3/1/1.

· Configure Router B and Router A to operate in broadcast client mode and receive broadcast messages on Ten-GigabitEthernet 3/1/1.

Figure 10 Network diagram

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Procedure

1. Assign an IP address to each interface, and make sure Router A, Router B, and Router C can reach each other, as shown in Figure 10. (Details not shown.)

2. Configure Router C:

# Enable the NTP service.

<RouterC> system-view

[RouterC] ntp-service enable

# Specify NTP for obtaining the time.

[RouterC] clock protocol ntp

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

[RouterC] ntp-service refclock-master 2

# Configure Router C to operate in broadcast server mode and send broadcast messages from Ten-GigabitEthernet 3/1/1.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] ntp-service broadcast-server

[RouterC-Ten-GigabitEthernet3/1/1] quit

3. Configure Router A:

# Enable the NTP service.

<RouterA> system-view

[RouterA] ntp-service enable

# Specify NTP for obtaining the time.

[RouterA] clock protocol ntp

# Configure Router A to operate in broadcast client mode and receive broadcast messages on Ten-GigabitEthernet 3/1/1.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] ntp-service broadcast-client

[RouterA-Ten-GigabitEthernet3/1/1] quit

4. Configure Router B:

# Enable the NTP service.

<RouterB> system-view

[RouterB] ntp-service enable

# Specify NTP for obtaining the time.

[RouterB] clock protocol ntp

# Configure Router B to operate in broadcast client mode and receive broadcast messages on Ten-GigabitEthernet 3/1/1.

[RouterB] interface ten-gigabitethernet 3/1/1

[RouterB-Ten-GigabitEthernet3/1/1] ntp-service broadcast-client

[RouterB-Ten-GigabitEthernet3/1/1] quit

Verifying the configuration

The following procedure uses Router A as an example to verify the configuration.

# Verify that Router A has synchronized its time with Router C, and the clock stratum level of Router A is 3.

[RouterA-Ten-GigabitEthernet3/1/1] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 3.0.1.31

Local mode: bclient

Reference clock ID: 3.0.1.31

Leap indicator: 00

Clock jitter: 0.044281 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00229 ms

Root dispersion: 4.12572 ms

Reference time: d0d289fe.ec43c720 Sat, Jan 8 2011 7:00:14.922

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between Router A and Router C.

[RouterA-Ten-GigabitEthernet3/1/1] display ntp-service sessions

source reference stra reach poll now offset delay disper

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

[1245]3.0.1.31 127.127.1.0 2 1 64 519 -0.0 0.0022 4.1257

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

Total sessions: 1

Example: Configuring NTP multicast association mode

Network configuration

As shown in Figure 11, configure Router C as the NTP server for multiple devices on different network segments so that these devices synchronize the time with Router C.

· Configure Router C's local clock as its reference source, with stratum level 2.

· Configure Router C to operate in multicast server mode and send multicast messages from Ten-GigabitEthernet 3/1/1.

· Configure Router D and Router A to operate in multicast client mode and receive multicast messages on Ten-GigabitEthernet 3/1/1.

Figure 11 Network diagram

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Procedure

1. Assign an IP address to each interface, and make sure the routers can reach each other, as shown in Figure 11. (Details not shown.)

2. Configure Router C:

# Enable the NTP service.

<RouterC> system-view

[RouterC] ntp-service enable

# Specify NTP for obtaining the time.

[RouterC] clock protocol ntp

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

[RouterC] ntp-service refclock-master 2

# Configure Router C to operate in multicast server mode and send multicast messages from Ten-GigabitEthernet 3/1/1.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] ntp-service multicast-server

[RouterC-Ten-GigabitEthernet3/1/1] quit

3. Configure Router D:

# Enable the NTP service.

<RouterD> system-view

[RouterD] ntp-service enable

# Specify NTP for obtaining the time.

[RouterD] clock protocol ntp

# Configure Router D to operate in multicast client mode and receive multicast messages on Ten-GigabitEthernet 3/1/1.

[RouterD] interface ten-gigabitethernet 3/1/1

[RouterD-Ten-GigabitEthernet3/1/1] ntp-service multicast-client

[RouterD-Ten-GigabitEthernet3/1/1] quit

4. Verify the configuration:

# Verify that Router D has synchronized its time with Router C, and the clock stratum level of Router D is 3.

Router D and Router C are on the same subnet, so Router D can receive multicast messages from Router C without being enabled with the multicast function.

[RouterD-Ten-GigabitEthernet3/1/1] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 3.0.1.31

Local mode: bclient

Reference clock ID: 3.0.1.31

Leap indicator: 00

Clock jitter: 0.044281 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00229 ms

Root dispersion: 4.12572 ms

Reference time: d0d289fe.ec43c720 Sat, Jan 8 2011 7:00:14.922

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between Router D and Router C.

[RouterD-Ten-GigabitEthernet3/1/1] display ntp-service sessions

source reference stra reach poll now offset delay disper

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

[1245]3.0.1.31 127.127.1.0 2 1 64 519 -0.0 0.0022 4.1257

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

Total sessions: 1

5. Configure Router B:

Because Router A and Router C are on different subnets, you must enable the multicast functions on Router B before Router A can receive multicast messages from Router C.

# Enable the IP multicast function.

<RouterB> system-view

[RouterB] multicast routing

[RouterB-mrib] quit

[RouterB] interface ten-gigabitethernet 3/1/1

[RouterB-Ten-GigabitEthernet3/1/1] igmp enable

[RouterB-Ten-GigabitEthernet3/1/1] igmp static-group 224.0.1.1

[RouterB-Ten-GigabitEthernet3/1/1] quit

[RouterB] interface ten-gigabitethernet 3/1/2

[RouterB-Ten-GigabitEthernet3/1/2] pim dm

[RouterB-Ten-GigabitEthernet3/1/2] quit

6. Configure Router A:

# Enable the NTP service.

<RouterA> system-view

[RouterA] ntp-service enable

# Specify NTP for obtaining the time.

[RouterA] clock protocol ntp

# Configure Router A to operate in multicast client mode and receive multicast messages from Ten-GigabitEthernet 3/1/1.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] ntp-service multicast-client

[RouterA-Ten-GigabitEthernet3/1/1] quit

Verifying the configuration

# Verify that Router A has synchronized its time with Router C, and the clock stratum level of Router A is 3.

[RouterA-Ten-GigabitEthernet3/1/1] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 3.0.1.31

Local mode: bclient

Reference clock ID: 3.0.1.31

Leap indicator: 00

Clock jitter: 0.165741 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00534 ms

Root dispersion: 4.51282 ms

Reference time: d0c61289.10b1193f Wed, Dec 29 2010 20:03:21.065

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between Router A and Router C.

[RouterA-Ten-GigabitEthernet3/1/1] display ntp-service sessions

source reference stra reach poll now offset delay disper

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

[1234]3.0.1.31 127.127.1.0 2 247 64 381 -0.0 0.0053 4.5128

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

Total sessions: 1

Example: Configuring IPv6 NTP multicast association mode

Network configuration

As shown in Figure 12, configure Router C as the NTP server for multiple devices on different network segments so that these devices synchronize the time with Router C.

· Configure Router C's local clock as its reference source, with stratum level 2.

· Configure Router C to operate in IPv6 multicast server mode and send IPv6 NTP multicast messages from Ten-GigabitEthernet 3/1/1.

· Configure Router D and Router A to operate in multicast client mode and receive IPv6 multicast messages on Ten-GigabitEthernet 3/1/1.

Figure 12 Network diagram

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Procedure

1. Assign an IP address to each interface, and make sure the routers can reach each other, as shown in Figure 12. (Details not shown.)

2. Configure Router C:

# Enable the NTP service.

<RouterC> system-view

[RouterC] ntp-service enable

# Specify NTP for obtaining the time.

[RouterC] clock protocol ntp

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

[RouterC] ntp-service refclock-master 2

# Configure Router C to operate in IPv6 multicast server mode and send multicast messages from Ten-GigabitEthernet 3/1/1.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] ntp-service ipv6 multicast-server ff24::1

[RouterC-Ten-GigabitEthernet3/1/1] quit

3. Configure Router D:

# Enable the NTP service.

<RouterD> system-view

[RouterD] ntp-service enable

# Specify NTP for obtaining the time.

[RouterD] clock protocol ntp

# Configure Router D to operate in IPv6 multicast client mode and receive multicast messages on Ten-GigabitEthernet 3/1/1.

[RouterD] interface ten-gigabitethernet 3/1/1

[RouterD-Ten-GigabitEthernet3/1/1] ntp-service ipv6 multicast-client ff24::1

[RouterD-Ten-GigabitEthernet3/1/1] quit

4. Verify the configuration:

# Verify that Router D has synchronized its time with Router C, and the clock stratum level of Router D is 3.

Router D and Router C are on the same subnet, so Router D can receive the IPv6 multicast messages from Router C without being enabled with the IPv6 multicast functions.

[RouterD-Ten-GigabitEthernet3/1/1] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 3000::2

Local mode: bclient

Reference clock ID: 165.84.121.65

Leap indicator: 00

Clock jitter: 0.000977 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00000 ms

Root dispersion: 8.00578 ms

Reference time: d0c60680.9754fb17 Wed, Dec 29 2010 19:12:00.591

Sync state from NTP server to local clock: clock synced

# Verify that an IPv6 NTP association has been established between Router D and Router C.

[RouterD-Ten-GigabitEthernet3/1/1] display ntp-service ipv6 sessions

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

Source: [1234]3000::2

Reference: 127.127.1.0 Clock stratum: 2

Reachabilities: 111 Poll interval: 64

Last receive time: 23 Offset: -0.0

Roundtrip delay: 0.0 Dispersion: 0.0

Total sessions: 1

5. Configure Router B:

Because Router A and Router C are on different subnets, you must enable the multicast functions on Router B so that Router A can receive IPv6 multicast messages from Router C.

# Enable the IPv6 multicast function.

<RouterB> system-view

[RouterB] ipv6 multicast routing

[RouterB-mrib6] quit

[RouterB] interface ten-gigabitethernet 3/1/1

[RouterB-Ten-GigabitEthernet3/1/1] mld enable

[RouterB-Ten-GigabitEthernet3/1/1] mld static-group ff24::1

[RouterB-Ten-GigabitEthernet3/1/1] quit

[RouterB] interface ten-gigabitethernet 3/1/2

[RouterB-Ten-GigabitEthernet3/1/2] ipv6 pim dm

[RouterB-Ten-GigabitEthernet3/1/2] quit

6. Configure Router A:

# Enable the NTP service.

<RouterA> system-view

[RouterA] ntp-service enable

# Specify NTP for obtaining the time.

[RouterA] clock protocol ntp

# Configure Router A to operate in IPv6 multicast client mode and receive multicast messages from Ten-GigabitEthernet 3/1/1.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] ntp-service ipv6 multicast-client ff24::1

[RouterA-Ten-GigabitEthernet3/1/1] quit

Verifying the configuration

# Verify that Router A has synchronized to Router C, and the clock stratum level is 3 on Router A and 2 on Router C.

[RouterA-Ten-GigabitEthernet3/1/1] display ntp status

Clock status: synchronized

Clock stratum: 3

System peer: 3000::2

Local mode: bclient

Reference clock ID: 165.84.121.65

Leap indicator: 00

Clock jitter: 0.165741 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00534 ms

Root dispersion: 4.51282 ms

Reference time: d0c61289.10b1193f Wed, Dec 29 2010 20:03:21.065

Sync state from NTP server to local clock: clock synced

# Verify that an IPv6 NTP association has been established between Router A and Router C.

[RouterA-Ten-GigabitEthernet3/1/1] display ntp-service ipv6 sessions

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

Source: [124]3000::2

Reference: 127.127.1.0 Clock stratum: 2

Reachabilities: 2 Poll interval: 64

Last receive time: 71 Offset: -0.0

Roundtrip delay: 0.0 Dispersion: 0.0

Total sessions: 1

Example: Configuring NTP authentication in broadcast mode

Network configuration

As shown in Figure 13, configure Router C as the NTP server for multiple devices on the same segment so that these devices synchronize the time with Router C. Configure Router A and Router B to authenticate the NTP server.

· Configure Router C's local clock as its reference source, with stratum level 3.

· Configure Router C to operate in broadcast server mode and send broadcast messages from Ten-GigabitEthernet 3/1/1.

· Configure Router A and Router B to operate in broadcast client mode and receive broadcast messages on Ten-GigabitEthernet 3/1/1.

· Configure NTP authentication on Router A, Router B, and Router C.

Figure 13 Network diagram

‌

Procedure

1. Assign an IP address to each interface, and make sure Router A, Router B, and Router C can reach each other, as shown in Figure 13. (Details not shown.)

2. Configure Router A:

# Enable the NTP service.

<RouterA> system-view

[RouterA] ntp-service enable

# Specify NTP for obtaining the time.

[RouterA] clock protocol ntp

# Enable NTP authentication on Router A. Create a plaintext NTP authentication key, with key ID of 88 and key value of 123456. Specify it as a trusted key.

[RouterA] ntp-service authentication enable

[RouterA] ntp-service authentication-keyid 88 authentication-mode md5 simple 123456

[RouterA] ntp-service reliable authentication-keyid 88

# Configure Router A to operate in broadcast client mode and receive NTP broadcast messages on Ten-GigabitEthernet 3/1/1.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] ntp-service broadcast-client

[RouterA-Ten-GigabitEthernet3/1/1] quit

3. Configure Router B:

# Enable the NTP service.

<RouterB> system-view

[RouterB] ntp-service enable

# Specify NTP for obtaining the time.

[RouterB] clock protocol ntp

# Enable NTP authentication on Router B. Create a plaintext NTP authentication key, with key ID of 88 and key value of 123456. Specify it as a trusted key.

[RouterB] ntp-service authentication enable

[RouterB] ntp-service authentication-keyid 88 authentication-mode md5 simple 123456

[RouterB] ntp-service reliable authentication-keyid 88

# Configure Router B to operate in broadcast client mode and receive NTP broadcast messages on Ten-GigabitEthernet 3/1/1.

[RouterB] interface ten-gigabitethernet 3/1/1

[RouterB-Ten-GigabitEthernet3/1/1] ntp-service broadcast-client

[RouterB-Ten-GigabitEthernet3/1/1] quit

4. Configure Router C:

# Enable the NTP service.

<RouterC> system-view

[RouterC] ntp-service enable

# Specify NTP for obtaining the time.

[RouterC] clock protocol ntp

# Specify the local clock as the reference source, with stratum level 3.

[RouterC] ntp-service refclock-master 3

# Configure Router C to operate in the NTP broadcast server mode and use Ten-GigabitEthernet 3/1/1 to send NTP broadcast messages.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] ntp-service broadcast-server

[RouterC-Ten-GigabitEthernet3/1/1] quit

5. Verify the configuration:

NTP authentication is enabled on Router A and Router B, but not enabled on Router C. Router A and Router B cannot synchronize their local clocks with Router C.

[RouterB-Ten-GigabitEthernet3/1/1] display ntp-service status

Clock status: unsynchronized

Clock stratum: 16

Reference clock ID: none

6. Configure NTP authentication on Router C:

# Enable NTP authentication on Router C. Create a plaintext NTP authentication key, with key ID of 88 and key value of 123456. Specify it as a trusted key.

[RouterC] ntp-service authentication enable

[RouterC] ntp-service authentication-keyid 88 authentication-mode md5 simple 123456

[RouterC] ntp-service reliable authentication-keyid 88

# Specify Router C as an NTP broadcast server, and associate key 88 with Router C.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] ntp-service broadcast-server authentication-keyid 88

Verifying the configuration

# Verify that Router B has synchronized its time with Router C, and the clock stratum level of Router B is 4.

[RouterB-Ten-GigabitEthernet3/1/1] display ntp-service status

Clock status: synchronized

Clock stratum: 4

System peer: 3.0.1.31

Local mode: bclient

Reference clock ID: 3.0.1.31

Leap indicator: 00

Clock jitter: 0.006683 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00127 ms

Root dispersion: 2.89877 ms

Reference time: d0d287a7.3119666f Sat, Jan 8 2011 6:50:15.191

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between Router B and Router C.

[RouterB-Ten-GigabitEthernet3/1/1] display ntp-service sessions

source reference stra reach poll now offset delay disper

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

[1245]3.0.1.31 127.127.1.0 3 3 64 68 -0.0 0.0000 0.0

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

Total sessions: 1

Example: Configuring MPLS L3VPN network time synchronization in client/server mode

Network configuration

As shown in Figure 14, two MPLS L3VPN instances are present on PE 1 and PE 2: vpn1 and vpn2. CE 1 and CE 3 are devices in VPN 1.

To synchronize time between PE 2 and CE 1 in VPN 1, perform the following tasks:

· Configure CE 1's local clock as its reference source, with stratum level 2.

· Configure CE 1 in the VPN instance vpn1 as the NTP server of PE 2.

Figure 14 Network diagram

Device	Interface	IP address	Device	Interface	IP address
CE 1	Ser3/1/1:0	10.1.1.1/24	PE 1	Ser3/1/1:0	10.1.1.2/24
CE 2	Ser3/1/1:0	10.2.1.1/24		Ser3/1/2:0	172.1.1.1/24
CE 3	Ser3/1/1:0	10.3.1.1/24		Ser3/1/3:0	10.2.1.2/24
CE 4	Ser3/1/1:0	10.4.1.1/24	PE 2	Ser3/1/1:0	10.3.1.2/24
P	Ser3/1/1:0	172.1.1.2/24		Ser3/1/2:0	172.2.1.2/24
	Ser3/1/2:0	172.2.1.1/24		Ser3/1/3:0	10.4.1.2/24

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Procedure

Before you perform the following configuration, be sure you have completed MPLS L3VPN-related configurations. For information about configuring MPLS L3VPN, see MPLS Configuration Guide.

1. Assign an IP address to each interface, as shown in Figure 14. Make sure CE 1 and PE 1, PE 1 and PE 2, and PE 2 and CE 3 can reach each other. (Details not shown.)

2. Configure CE 1:

# Enable the NTP service.

<CE1> system-view

[CE1] ntp-service enable

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

[CE1] ntp-service refclock-master 2

3. Configure PE 2:

# Enable the NTP service.

<PE2> system-view

[PE2] ntp-service enable

# Specify NTP for obtaining the time.

[PE2] clock protocol ntp

# Specify CE 1 in the VPN instance vpn1 as the NTP server of PE 2.

[PE2] ntp-service unicast-server 10.1.1.1 vpn-instance vpn1

Verifying the configuration

# Verify that PE 2 has synchronized to CE 1, with stratum level 3.

[PE2] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 10.1.1.1

Local mode: client

Reference clock ID: 10.1.1.1

Leap indicator: 00

Clock jitter: 0.005096 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00655 ms

Root dispersion: 1.15869 ms

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

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between PE 2 and CE 1.

[PE2] display ntp-service sessions

source reference stra reach poll now offset delay disper

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

[1245]10.1.1.1 127.127.1.0 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

# Verify that server 127.0.0.1 has synchronized to server 10.1.1.1, and server 10.1.1.1 has synchronized to the local clock.

[PE2] display ntp-service trace

Server 127.0.0.1

Stratum 3 , jitter 0.000, synch distance 796.50.

Server 10.1.1.1

Stratum 2 , jitter 939.00, synch distance 0.0000.

RefID 127.127.1.0

Example: Configuring MPLS L3VPN network time synchronization in symmetric active/passive mode

Network configuration

As shown in Figure 15, two VPN instances are present on PE 1 and PE 2: vpn1 and vpn2. CE 1 and CE 3 belong to VPN 1.

To synchronize time between PE 1 and CE 1 in VPN 1, perform the following tasks:

· Configure CE 1's local clock as its reference source, with stratum level 2.

· Configure CE 1 in the VPN instance vpn1 as the symmetric passive peer of PE 1.

Figure 15 Network diagram

Device	Interface	IP address	Device	Interface	IP address
CE 1	Ser3/1/1:0	10.1.1.1/24	PE 1	Ser3/1/1:0	10.1.1.2/24
CE 2	Ser3/1/1:0	10.2.1.1/24		Ser3/1/2:0	172.1.1.1/24
CE 3	Ser3/1/1:0	10.3.1.1/24		Ser3/1/3:0	10.2.1.2/24
CE 4	Ser3/1/1:0	10.4.1.1/24	PE 2	Ser3/1/1:0	10.3.1.2/24
P	Ser3/1/1:0	172.1.1.2/24		Ser3/1/2:0	172.2.1.2/24
	Ser3/1/2:0	172.2.1.1/24		Ser3/1/3:0	10.4.1.2/24

‌

Procedure

Before you perform the following configuration, be sure you have completed MPLS L3VPN-related configurations. For information about configuring MPLS L3VPN, see MPLS Configuration Guide.

1. Assign an IP address to each interface, as shown in Figure 15. Make sure CE 1 and PE 1, PE 1 and PE 2, PE 2 and CE 3 can reach each other. (Details not shown.)

2. Configure CE 1:

# Enable the NTP service.

<CE1> system-view

[CE1] ntp-service enable

# Specify NTP for obtaining the time.

[CE1] clock protocol ntp

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

[CE1] ntp-service refclock-master 2

3. Configure PE 1:

# Enable the NTP service.

<PE1> system-view

[PE1] ntp-service enable

# Specify NTP for obtaining the time.

[PE1] clock protocol ntp

# Specify CE 1 in the vpn instance vpn1 as the symmetric passive peer of PE 1.

[PE1] ntp-service unicast-peer 10.1.1.1 vpn-instance vpn1

Verifying the configuration

# Verify that PE 1 has synchronized to CE 1, with stratum level 3.

[PE1] display ntp-service status

Clock status: synchronized

Clock stratum: 3

System peer: 10.1.1.1

Local mode: sym_active

Reference clock ID: 10.1.1.1

Leap indicator: 00

Clock jitter: 0.005096 s

Stability: 0.000 pps

Clock precision: 2^-18

Root delay: 0.00655 ms

Root dispersion: 1.15869 ms

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

Sync state from NTP server to local clock: clock synced

# Verify that an IPv4 NTP association has been established between PE 1 and CE 1.

[PE1] display ntp-service sessions

source reference stra reach poll now offset delay disper

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

[1245]10.1.1.1 127.127.1.0 2 1 64 519 -0.0 0.0000 0.0

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

Total sessions: 1

# Verify that server 127.0.0.1 has synchronized to server 10.1.1.1, and server 10.1.1.1 has synchronized to the local clock.

[PE1] display ntp-service trace

Server 127.0.0.1

Stratum 3 , jitter 0.000, synch distance 796.50.

Server 10.1.1.1

Stratum 2 , jitter 939.00, synch distance 0.0000.

RefID 127.127.1.0

Configuring SNTP

About SNTP

SNTP is a simplified, client-only version of NTP specified in RFC 4330. It uses the same packet format and packet exchange procedure as NTP, but provides faster synchronization at the price of time accuracy.

SNTP working mode

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.

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.

Protocols and standards

RFC 4330, Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI

Restrictions and guidelines: SNTP configuration

When you configure SNTP, follow these restrictions and guidelines:

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

· You must use the clock protocol command to specify NTP for obtaining the time. For more information about the clock protocol command, see device management commands in Fundamentals Configuration Guide.

SNTP tasks at a glance

To configure SNTP, perform the following tasks:

1. Enabling the SNTP service

2. Specifying an NTP server for the device

3. (Optional.)

4. Configuring SNTP authentication

(Optional.)

5. Specifying the SNTP time-offset thresholds for log and trap outputs

Enabling the SNTP service

Restrictions and guidelines

The NTP service and SNTP service are mutually exclusive. Before you enable SNTP, make sure NTP is disabled.

Procedure

1. Enter system view.

system-view

2. Enable the SNTP service.

sntp enable

By default, the SNTP service is disabled.

Specifying an NTP server for the device

Restrictions and guidelines

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.

Procedure

1. Enter system view.

system-view

2. Specify an NTP server for the device.

IPv4:

sntp unicast-server { server-name | ip-address } [ vpn-instance vpn-instance-name ] [ authentication-keyid keyid | source interface-type interface-number | version number ] *

IPv6:

sntp ipv6 unicast-server { server-name | ipv6-address } [ vpn-instance vpn-instance-name ] [ authentication-keyid keyid | source interface-type interface-number ] *

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

You can specify multiple NTP servers for the client by repeating this step.

To perform authentication, you need to specify the authentication-keyid keyid option.

Configuring SNTP authentication

About this task

SNTP authentication ensures that an SNTP client is synchronized only to an authenticated trustworthy NTP server.

Restrictions and guidelines

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

Use the same authentication key ID, algorithm, 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.

Procedure

1. Enter system view.

system-view

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 { hmac-sha-1 | hmac-sha-256 | hmac-sha-384 | hmac-sha-512 | md5 } { cipher | simple } string [ acl ipv4-acl-number | ipv6 acl ipv6-acl-number ] *

By default, no SNTP authentication key exists.

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.

IPv4:

sntp unicast-server { server-name | ip-address } [ vpn-instance vpn-instance-name ] authentication-keyid keyid

IPv6:

sntp ipv6 unicast-server { server-name | ipv6-address } [ vpn-instance vpn-instance-name ] authentication-keyid keyid

By default, no NTP server is specified.

Specifying the SNTP time-offset thresholds for log and trap outputs

About this task

By default, the SNTP client synchronizes the time with the server and outputs a log and a trap when the time offset between the client and server exceeds 128 ms for multiple times.

After you set the SNTP time-offset thresholds for log and trap outputs, the SNTP client synchronizes the time with the server when the time offset exceeds 128 ms for multiple times, but outputs a log or trap only when the time offset exceeds the specified threshold.

Procedure

1. Enter system view.

system-view

2. Specify the SNTP time-offset thresholds for log and trap outputs.

sntp time-offset-threshold { log log-threshold | trap trap-threshold } *

By default, no SNTP time-offset thresholds are set for log and trap outputs.

Display and maintenance commands for 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 examples

Example: Configuring SNTP

Network configuration

As shown in Figure 16, perform the following tasks:

· Configure Device A's local clock as its reference source, with stratum level 2.

· Configure Device B to operate in SNTP client mode, and specify Device A as the NTP server.

· Configure NTP authentication on Device A and SNTP authentication on Device B.

Figure 16 Network diagram

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Procedure

1. Assign an IP address to each interface, and make sure Device A and Device B can reach each other, as shown in Figure 16. (Details not shown.)

2. Configure Device A:

# Enable the NTP service.

<DeviceA> system-view

[DeviceA] ntp-service enable

# Specify NTP for obtaining the time.

[DeviceA] clock protocol ntp

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

[DeviceA] ntp-service refclock-master 2

# Enable NTP authentication on Device A.

[DeviceA] ntp-service authentication enable

# Configure a plaintext NTP authentication key, with key ID of 10 and key value of aNiceKey.

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

# Specify the key as a trusted key.

[DeviceA] ntp-service reliable authentication-keyid 10

3. Configure Device B:

# Enable the SNTP service.

<DeviceB> system-view

[DeviceB] sntp enable

# Specify NTP for obtaining the time.

[DeviceB] clock protocol ntp

# Enable SNTP authentication on Device B.

[DeviceB] sntp authentication enable

# Configure a plaintext authentication key, with key ID of 10 and key value of aNiceKey.

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

# Specify the key as a trusted key.

[DeviceB] sntp reliable authentication-keyid 10

# Specify Device A as the NTP server of Device B, and associate the server with key 10.

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

Verifying the configuration

# Verify that an SNTP association has been established between Device B and Device A, and Device B has synchronized its time with Device A.

[DeviceB] 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)

15-Network Management and Monitoring Configuration Guide

NTP application scenarios

NTP architecture

NTP access control

NTP authentication

Restrictions and guidelines: NTP configuration

Restrictions and guidelines

Procedure

Configuring NTP association mode

Restrictions and guidelines

Configuring the NTP client

Configuring the NTP server

Restrictions and guidelines

Procedure

Restrictions and guidelines

Configuring the broadcast client

Configuring the broadcast server

Restrictions and guidelines

Configuring a multicast client

Configuring the multicast server

Configuring the local clock as the reference source

About this task

Restrictions and guidelines

Prerequisites

Procedure

Prerequisites

Restrictions and guidelines

Procedure

Configuring NTP authentication

Restrictions and guidelines

Configuring NTP authentication for a client

Configuring NTP authentication for a server

Restrictions and guidelines

Configuring NTP authentication for an active peer

Configuring NTP authentication for a passive peer

Restrictions and guidelines

Configuring NTP authentication for a broadcast client

Configuring NTP authentication for a broadcast server

Restrictions and guidelines

Configuring NTP authentication for a multicast client

Configuring NTP authentication for a multicast server

Controlling NTP packet sending and receiving

Restrictions and guidelines

Procedure

About this task

Procedure

Configuring the maximum number of dynamic associations

About this task

Restrictions and guidelines

Procedure

About this task

Procedure

Specifying the NTP time-offset thresholds for log and trap outputs

About this task

Procedure

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration