cisco Nexus 3000 Low-Latency Switches User Guide

cisco Nexus 3000 Low-Latency Switches

Information About NTP

The Network Time Protocol (NTP) synchronizes the time of day among a set of distributed time servers and clients so that you can correlate events when you receive system logs and other time-specific events from multiple network devices. NTP uses the User Datagram Protocol (UDP) as its transport protocol. All NTP communications use Coordinated Universal Time (UTC).
An NTP server usually receives its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server, and then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two machines to within a millisecond of each other.

NTP uses a stratum to describe the distance between a network device and an authoritative time source:

• A stratum 1 time server is directly attached to an authoritative time source (such as a radio or atomic clock or a GPS time source).
• A stratum 2 NTP server receives its time through NTP from a stratum 1 time server.

Before synchronizing, NTP compares the time reported by several network devices and does not synchronize with one that is significantly different, even if it is a stratum 1. Because Cisco NX-OS cannot connect to a radio or atomic clock and act as a stratum 1 server, we recommend that you use the public NTP servers available on the Internet. If the network is isolated from the Internet, Cisco NX-OS allows you to configure the time as though it were synchronized through NTP, even though it was not.

Note
You can create NTP peer relationships to designate the time-serving hosts that you want your network device to consider synchronizing with and to keep accurate time if a server failure occurs.

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

NTP as Time Server

Other devices can configure it as a time server. You can also configure the device to act as an authoritative NTP server, enabling it to distribute time even when it is not synchronized to an outside time source.

Distributing NTP Using CFS

Cisco Fabric Services (CFS) distributes the local NTP configuration to all Cisco devices in the network.
After enabling CFS on your device, a network-wide lock is applied to NTP whenever an NTP configuration is started. After making the NTP configuration changes, you can discard or commit them.
In either case, the CFS lock is then released from the NTP application.

Clock Manager

Clocks are resources that need to be shared across different processes.
Multiple time synchronization protocols, such as NTP and Precision Time Protocol (PTP), might be running in the system.

High Availability

Stateless restarts are supported for NTP. After a reboot or a supervisor switchover, the running configuration is applied.
You can configure NTP peers to provide redundancy in case an NTP server fails.

Virtualization Support

NTP recognizes virtual routing and forwarding (VRF) instances. NTP uses the default VRF if you do not configure a specific VRF for the NTP server and NTP peer.

Prerequisites for NTP

NTP has the following prerequisites:

• To configure NTP, you must have connectivity to at least one server that is running NTP.

Guidelines and Limitations for NTP

NTP has the following configuration guidelines and limitations:

• The show ntp session status CLI command does not show the last action time stamp, the last action, the last action result, and the last action failure reason.

• NTP server functionality is supported.

• You should have a peer association with another device only when you are sure that your clock is reliable (which means that you are a client of a reliable NTP server).

• A peer configured alone takes on the role of a server and should be used as a backup. If you have two servers, you can configure several devices to point to one server and the remaining devices to point to the other server. You can then configure a peer association between these two servers to create a more reliable NTP configuration.

• If you have only one server, you should configure all the devices as clients to that server.

• You can configure up to 64 NTP entities (servers and peers).

• If CFS is disabled for NTP, NTP does not distribute any configuration and does not accept a distribution from other devices in the network.

• After CFS distribution is enabled for NTP, the entry of an NTP configuration command locks the network for NTP configuration until a commit command is entered. During the lock, no changes can be made to the NTP configuration by any other device in the network except the device that initiated the lock.

• If you use CFS to distribute NTP, all devices in the network should have the same VRFs configured as you use for NTP.

• If you configure NTP in a VRF, ensure that the NTP server and peers can reach each other through the configured VRFs.

• You must manually distribute NTP authentication keys on the NTP server and Cisco NX-OS devices across the network.

• If you are using the switch as an edge device and want to use NTP, Cisco recommends using the ntp access-group command and filtering NTP only to the required edge devices.

• If the system has been configured with the ntp passive, ntp broadcast client, or ntp multicast client commands, when NTP receives an incoming symmetric active, broadcast, or multicast packet, it can set up an ephemeral peer association in order to synchronize with the sender.
  Note
  Make sure that you specify ntp authenticate before enabling any of the above commands. Failure to do so will allow your device to synchronize with any device that sends one of the above packet types, including malicious attacker- controlled devices.

• If the ntp authenticate command is specified, when a symmetric active, broadcast, or multicast packet is received, the system does not synchronize to the peer unless the packet carries one of the authentication keys specified in the ntp trusted-key global configuration command.

• To prevent synchronization with unauthorized network hosts, the ntp authenticate command should be specified any time the ntp passive, ntp broadcast client, or ntp multicast client command has been specified unless other measures, such as the ntp access-group command, have been taken to prevent unauthorized hosts from communicating with the NTP service on the device.

• The ntp authenticate command does not authenticate peer associations configured via the ntp server and ntp peer configuration commands. To authenticate the ntp server and ntp peer associations, specify the key keyword.

• Use NTP broadcast or multicast associations when time accuracy and reliability requirements are modest, your network is localized, and the network has more than 20 clients. We recommend that you use NTP broadcast or multicast associations in networks that have limited bandwidth, system memory, or CPU resources.

• A maximum of four ACLs can be configured for a single NTP access group.
  Note
  Time accuracy is marginally reduced in NTP broadcast associations because information flows only one way.

Default Settings

The following are the default settings for NTP parameters.

Configuring NTP

Enabling or Disabling NTP on an Interface

You can enable or disable NTP on a particular interface. NTP is enabled on all interfaces by default.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# interface type slot/port| Enters interface configuration mode.
Step 3| switch(config-if)# [no] ntp disable { ip | ipv6 }| Disables NTP IPv4 or IPv6 on the specified interface.
Use the no form of this command to reenable NTP on the interface.
Step 4| (Optional) switch(config-if)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
The following example shows how to enable or disable NTP on an interface:

• switch# configure terminal
• switch(config)# interface ethernet 6/1
• switch(config-if)# ntp disable ip
• switch(config-if)# copy running-config startup-config

Configuring the Device as an Authoritative NTP Server

You can configure the device to act as an authoritative NTP server, enabling it to distribute time even when it is not synchronized to an existing time server.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
| Command or Action| Purpose
---|---|---
Step 2| [ no ] ntp master [ stratum ]| Configures the device as an authoritative NTP server.

You can specify a different stratum level from which NTP clients get their time synchronized. The range is from 1 to 15.

Step 3| (Optional) show running-config ntp| Displays the NTP configuration.
Step 4| (Optional) switch(config)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
This example shows how to configure the Cisco NX-OS device as an authoritative NTP server with a different stratum level:

• switch# configure terminal
• Enter configuration commands, one per line. End with CNTL/Z.
• switch(config)# ntp master 5

Configuring an NTP Server and Peer

• You can configure an NTP server and peer.

Before you begin
Make sure that you know the IP address or DNS names of your NTP server and its peers.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# [ no ] ntp server { ip-address | ipv6-address | dns-name } [ key key-id ] [ maxpoll max-poll ] [ minpoll min-poll ] [ prefer ] [ use-vrf vrf-name ]| Forms an association with a server.

Use the key keyword to configure a key to be used while communicating with the NTP server.

The range for the key-id argument is from 1 to 65535.

Use the maxpoll and minpoll keywords to configure the maximum and minimum intervals in which to poll a server. The range for the max-poll and min-poll arguments is from 4 to 16 (configured as powers of 2, so effectively 16 to 65536 seconds), and the default values

| Command or Action| Purpose
---|---|---
| | are 6 and 4, respectively ( maxpoll default = 64 seconds, minpoll default = 16 seconds).
Use the prefer keyword to make this the preferred NTP server for the device.
Use the use-vrf keyword to configure the NTP server to communicate over the specified VRF.
The vrf-name argument can be default, management, or any case-sensitive alphanumeric string up to 32 characters.
Note If you configure a key to be used while communicating with the NTP server, make sure that the key exists as a trusted key on the device.
Step 3| switch(config)# [ no ] ntp peer { ip-address | ipv6-address | dns-name } [ key key-id ] [ maxpoll max-poll ] [ minpoll min-poll ] [ prefer ] [ use-vrf vrf-name ]| Forms an association with a peer. You can specify multiple peer associations.

Use the key keyword to configure a key to be used while communicating with the NTP peer. The range for the key-id argument is from 1 to 65535.
Use the maxpoll and minpoll keywords to configure the maximum and minimum intervals in which to poll a server. The range for the max-poll and min-poll arguments is from 4 to 17 (configured as powers of 2, so effectively 16 to 131072 seconds), and the default values are 6 and 4, respectively ( maxpoll default = 64 seconds, minpoll default = 16 seconds).
Use the prefer keyword to make this the preferred NTP peer for the device.
Use the use-vrf keyword to configure the NTP peer to communicate over the specified VRF. The vrf-name argument can be default , management , or any case-sensitive alphanumeric string up to 32 characters.

Step 4| (Optional) switch(config)# show ntp peers| Displays the configured server and peers.
Note ** A domain name is resolved only when you have a DNS server configured.
Step 5| (Optional) switch(config)# copy running-config startup- config**| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Configuring NTP Authentication

You can configure the device to authenticate the time sources to which the local clock is synchronized. When you enable NTP authentication, the device synchronizes to a time source only if the source carries one of the authentication keys specified by the ntp trusted-key command. The device drops any packets that fail the authentication check and prevents them from updating the local clock. NTP authentication is disabled by default.

Before you begin
Authentication for NTP servers and NTP peers is configured on a per- association basis using the key keyword on each ntp server and ntp peer command. Make sure that you configured all NTP server and peer associations with the authentication keys that you plan to specify in this procedure. Any ntp server or ntp peer commands that do not specify the key keyword will continue to operate without authentication.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| configure terminal

Example:

switch# configure terminal switch(config)#

| Enters global configuration mode.
Step 2| [ no ] ntp authentication-key number md5

md5- string

Example:

switch(config)# ntp authentication-key

42 md5 aNiceKey

| Defines the authentication keys. The device does not synchronize to a time source unless the source has one of these authentication keys and the key number is specified by the ntp trusted-key number command.

The range for authentication keys is from 1 to 65535. For the MD5 string, you can enter up to eight alphanumeric characters.

Step 3| ntp server ip-address key key-id
Example:
switch(config)# ntp server 192.0.2.1 key 1001| Enables authentication for the specified NTP server, forming an association with a server.

Use the key keyword to configure a key to be used while communicating with the NTP server. The range for the key-id argument is from 1 to 65535.

To require authentication, the key keyword must be used. Any ntp server or ntp peer commands that do not specify the key keyword will continue to operate without authentication.

Step 4| (Optional) show ntp authentication-keys
Example:
switch(config)# show ntp authentication-keys| Displays the configured NTP authentication keys.
| Command or Action| Purpose
---|---|---
Step 5| [ no ] ntp trusted-key number

Example:

switch(config)# ntp trusted-key 42

| Specifies one or more keys (defined in Step 2) that an unconfigured remote symmetric, broadcast, and multicast time source must provide in its NTP packets in order for the device to synchronize to it. The range for trusted keys is from 1 to 65535.

This command provides protection against accidentally synchronizing the device to a time source that is not trusted.

Step 6| (Optional) show ntp trusted-keys

Example:

switch(config)# show ntp trusted-keys

| Displays the configured NTP trusted keys.
Step 7| [ no ] ntp authenticate

Example:

switch(config)# ntp authenticate

| Enables or disables authentication for ntp passive, ntp broadcast client, and ntp multicast. NTP authentication is disabled by default.
Step 8| (Optional) show ntp authentication-status

Example:

switch(config)# show ntp authentication-status

| Displays the status of NTP authentication.
Step 9| (Optional) copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

| Copies the running configuration to the startup configuration.

Configuring NTP Access Restrictions

You can control access to NTP services by using access groups. Specifically, you can specify the types of requests that the device allows and the servers from which it accepts responses.
If you do not configure any access groups, NTP access is granted to all devices. If you configure any access groups, NTP access is granted only to the remote device whose source IP address passes the access list criteria.

Beginning with Cisco NX-OS Release 7.0(3)I7(3), access groups are evaluated in the following method:

• Without the match-all keyword, the packet gets evaluated against the access groups (in the order mentioned below) until it finds a permit. If a permit is not found, the packet is dropped.
• With match-all keyword, the packet gets evaluated against all the access groups (in the order mentioned below) and the action is taken based on the last successful evaluation (the last access group where an ACL is configured).

The mapping of the access group to the type of packet is as follows:

• peer—process client, symmetric active, symmetric passive, serve, control, and private packets(all types)
• serve—process client, control, and private packets
• serve-only—process client packets only
• query-only—process control and private packets only

The access groups are evaluated in the following descending order:

1. peer (all packet types)
2. serve (client, control, and private packets)
3. query only (client packets) or query-only (control and private packets)

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# [ no ] ntp access-group match-all | {{ peer | serve | serve-only | query-only } access-list-name }| Creates or removes an access group to control NTP access and applies a basic IP access list.
The access group options are scanned in the following order, from least restrictive to most restrictive. However, if NTP matches a deny ACL rule in a configured peer, ACL processing stops and does not continue to the next access group option.

• The peer keyword enables the device to receive time requests and NTP control queries and to synchronize itself to the servers specified in the access list.
• The serve keyword enables the device to receive time requests and NTP control queries from the servers specified in the access list but not to synchronize itself to the specified servers.
• The serve-only keyword enables the device to receive only time requests from servers specified in the access list.
• The query-only keyword enables the device to receive only NTP control queries from the servers specified in the access list.
• The match-all keyword enables the access group options to be scanned in the following order, from least restrictive to most restrictive: peer, serve, serve-only, query-only. If the incoming packet does not match the ACL in the peer access

| Command or Action| Purpose
---|---|---
| | group, it goes to the serve access group to be processed. If the packet does not match the ACL in the serve access group, it goes to the serve-only access group, and so on.

Note The match-all keyword is available beginning with Cisco NX-OS Release 7.0(3)I6(1).

Step 3| switch(config)# show ntp access-groups| (Optional) Displays the NTP access group configuration.
Step 4| (Optional) switch(config)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
This example shows how to configure the device to allow it to synchronize to a peer from access group “accesslist1”:

• switch# configure terminal

• switch(config)# ntp access-group peer accesslist1

• switch(config)# show ntp access-groups

• Access List Type —————————–

• accesslist1 Peer

• switch(config)# copy running-config startup-config
  [########################################] 100%

• switch(config)#

Configuring the NTP Source IP Address

NTP sets the source IP address for all NTP packets based on the address of the interface through which the NTP packets are sent. You can configure NTP to use a specific source IP address.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| [ no ] ntp source ip-address| Configures the source IP address for all NTP packets. The ip-address can be in IPv4 or IPv6 format.

Example
This example shows how to configure an NTP source IP address of 192.0.2.2.

• switch# configure terminal
• switch(config)# ntp source 192.0.2.2

Configuring the NTP Source Interface

You can configure NTP to use a specific interface.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| [ no ] ntp source-interface interface| Configures the source interface for all NTP packets. The following list contains the valid values for interface.

• ethernet
• loopback
• mgmt
• port-channel
• vlan

Example
This example shows how to configure the NTP source interface:

• switch# configure terminal
• switch(config)# ntp source-interface ethernet

Configuring an NTP Broadcast Server

You can configure an NTP IPv4 broadcast server on an interface.
The device then sends broadcast packets through that interface periodically.
The client is not required to send a response.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# interface type slot/port| Enters interface configuration mode.
Step 3| switch(config-if)# [no] ntp broadcast [ destination ip- address ] [ key key-id ] [ version number ]| Enables an NTP IPv4 broadcast server on the specified interface.

• destination ip-address —Configures the broadcast destination IP address.

| Command or Action| Purpose
---|---|---
| |

• key key-id —Configures the broadcast authentication key number. The range is from 1 to 65535.
• version number —Configures the NTP version. The range is from 2 to 4.

Step 4| switch(config-if)# exit| Exits interface configuration mode.
Step 5| (Optional) switch(config)# [no] ntp broadcastdelay delay| Configures the estimated broadcast round-trip delay in microseconds. The range is from 1 to 999999.
Step 6| (Optional) switch(config)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
This example shows how to configure an NTP broadcast server:

• switch# configure terminal
• switch(config)# interface ethernet 6/1
• switch(config-if)# ntp broadcast destination 192.0.2.10 switch(config-if)# exit
• switch(config)# ntp broadcastdelay 100
• switch(config)# copy running-config startup-config

Configuring an NTP Multicast Server

You can configure an NTP IPv4 or IPv6 multicast server on an interface.
The device then sends multicast packets through that interface periodically.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# interface type slot/port| Enters interface configuration mode.
Step 3| switch(config-if)# [no] ntp multicast
[ ipv4-address | ipv6-address ] [ key key-id ] [ ttl value ] [ version number ]| Enables an NTP IPv4 or IPv6 multicast server on the specified interface.

• = ipv4-address or ipv6-address — Multicast IPv4 or IPv6 address.
• key key-id —Configures the broadcast authentication key number. The range is from 1 to 65535.
• ttl value —Time-to-live value of the multicast packets. The range is from 1 to 255.

| Command or Action| Purpose
---|---|---
| |

• version number —NTP version. The range is from 2 to 4.

Step 4| (Optional) switch(config-if)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
This example shows how to configure an Ethernet interface to send NTP multicast packets:

• switch# configure terminal
• switch(config)# interface ethernet 2/2
• switch(config-if)# ntp multicast FF02::1:FF0E:8C6C
• switch(config-if)# copy running-config startup-config

Configuring an NTP Multicast Client

You can configure an NTP multicast client on an interface. The device then listens to NTP multicast messages and discards any messages that come from an interface for which multicast is not configured.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# interface type slot/port| Enters interface configuration mode.
Step 3| switch(config-if)# [no] ntp multicast client [ ipv4-address | ipv6-address ]| Enables the specified interface to receive NTP multicast packets.
Step 4| (Optional) switch(config-if)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
This example shows how to configure an Ethernet interface to receive NTP multicast packets:

• switch# configure terminal
• switch(config)# interface ethernet 2/3
• switch(config-if)# ntp multicast client FF02::1:FF0E:8C6C
• switch(config-if)# copy running-config startup-config

Configuring NTP Logging

You can configure NTP logging in order to generate system logs with significant NTP events. NTP logging is disabled by default.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# [ no ] ntp logging| Enables or disables system logs to be generated with significant NTP events. NTP logging is disabled by default.
Step 3| (Optional) switch(config)# show ntp logging-status| Displays the NTP logging configuration status.
Step 4| (Optional) switch(config)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
The following example shows how to enable NTP logging in order to generate system logs with significant NTP events:

• switch# configure terminal

• switch(config)# ntp logging

• switch(config)# copy running-config startup-config
  [########################################] 100%

• switch(config)#

Enabling CFS Distribution for NTP

You can enable CFS distribution for NTP in order to distribute the NTP configuration to other CFS-enabled devices.

Before you begin
Make sure that you have enabled CFS distribution for the device.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# [ no ] ntp distribute| Enables or disables the device to receive NTP configuration updates that are distributed through CFS.
Step 3| (Optional) switch(config)# show ntp status| Displays the NTP CFS distribution status.
Step 4| (Optional) switch(config)# copy running-config startup- config| Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

Example
This example shows how to enable the device to receive NTP configuration updates through CFS:

• switch# configure terminal
• switch(config)# ntp distribute
• switch(config)# copy running-config startup-config

Committing NTP Configuration Changes

When you commit the NTP configuration changes, the effective database is overwritten by the configuration changes in the pending database and all the devices in the network receive the same configuration.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# ntp commit| Distributes the NTP configuration changes to all Cisco NX-OS devices in the network and releases the CFS lock. This command overwrites the effective database with the changes made to the pending database.

Discarding NTP Configuration Changes

After making the configuration changes, you can choose to discard the changes instead of committing them. If you discard the changes, Cisco NX-OS removes the pending database changes and releases the CFS lock.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# ntp abort| Discards the NTP configuration changes in the pending database and releases the CFS lock. Use this command on the device where you started the NTP configuration.

Releasing the CFS Session Lock

If you have performed an NTP configuration and have forgotten to release the lock by either committing or discarding the changes, you or another administrator can release the lock from any device in the network.
This action also discards pending database changes.

Procedure

| Command or Action| Purpose
---|---|---
Step 1| switch# configure terminal| Enters global configuration mode.
Step 2| switch(config)# clear ntp session| Discards the NTP configuration changes in the pending database and releases the CFS lock.

Verifying the NTP Configuration

keys.
show ntp authentication-status| Displays the status of NTP authentication.
show ntp logging-status| Displays the NTP logging status.
show ntp peer-status| Displays the status for all NTP servers and peers.
show ntp peer| Displays all the NTP peers.
show ntp pending| Displays the temporary CFS database for NTP.
show ntp pending-diff| Displays the difference between the pending CFS database and the current NTP configuration.
show ntp rts-update| Displays the RTS update status.
show ntp session status| Displays the NTP CFS distribution session information.
show ntp source| Displays the configured NTP source IP address.
show ntp source-interface| Displays the configured NTP source interface.
show ntp statistics { io | local | memory | peer

{ ipaddr { ipv4-addr } | name peer-name }}

| Displays the NTP statistics.
show ntp status| Displays the NTP CFS distribution status.
show ntp trusted-keys| Displays the configured NTP trusted keys.
show running-config ntp| Displays NTP information.

Configuration Examples for NTP

Configuration Examples for NTP
This example shows how to configure an NTP server and peer, enable NTP authentication, enable NTP logging, and then save the startup configuration so that it is saved across reboots and restarts:

• switch# configure terminal

• Enter configuration commands, one per line. End with CNTL/Z.

• switch(config)# ntp server 192.0.2.105 key 42

• switch(config)# ntp peer 192.0.2.105

• switch(config)# show ntp peers ———————–

• Peer IP Address Serv/Peer —————————–

• 192.0.2.100 Peer (configured)

• 192.0.2.105 Server (configured)

• switch(config)# ntp authentication-key 42 md5 aNiceKey

• switch(config)# show ntp authentication-keys ———————-

• Auth key MD5 String —————————–

• 42 aNicekey

• switch(config)# ntp trusted-key 42

• switch(config)# show ntp trusted-keys

• Trusted Keys: 42

• switch(config)# ntp authenticate

• switch(config)# show ntp authentication-status

• Authentication enabled.

• switch(config)# ntp logging

• switch(config)# show ntp logging

• NTP logging enabled.

• switch(config)# copy running-config startup-config
  [########################################] 100%

• switch(config)#

This example shows an NTP access group configuration with the following restrictions:

• Peer restrictions are applied to IP addresses that pass the criteria of the access list named “peer-acl.”
• Serve restrictions are applied to IP addresses that pass the criteria of the access list named “serve-acl.”
• Serve-only restrictions are applied to IP addresses that pass the criteria of the access list named “serve-only-acl.”
• Query-only restrictions are applied to IP addresses that pass the criteria of the access list named “query-only-acl.”

switch# configure terminal

• switch(config)# ntp peer 10.1.1.1
• switch(config)# ntp peer 10.2.2.2
• switch(config)# ntp peer 10.3.3.3
• switch(config)# ntp peer 10.4.4.4
• switch(config)# ntp peer 10.5.5.5
• switch(config)# ntp peer 10.6.6.6
• switch(config)# ntp peer 10.7.7.7
• switch(config)# ntp peer 10.8.8.8
• switch(config)# ntp access-group peer peer-acl
• switch(config)# ntp access-group serve serve-acl
• switch(config)# ntp access-group serve-only serve-only-acl
• switch(config)# ntp access-group query-only query-only-acl
• switch(config)# ip access-list peer-acl
• switch(config-acl)# 10 permit ip host 10.1.1.1 any
• switch(config-acl)# 20 permit ip host 10.8.8.8 any
• switch(config)# ip access-list serve-acl
• switch(config-acl)# 10 permit ip host 10.4.4.4 any
• switch(config-acl)# 20 permit ip host 10.5.5.5 any
• switch(config)# ip access-list serve-only-acl
• switch(config-acl)# 10 permit ip host 10.6.6.6 any
• switch(config-acl)# 20 permit ip host 10.7.7.7 any
• switch(config)# ip access-list query-only-acl
• switch(config-acl)# 10 permit ip host 10.2.2.2 any
• switch(config-acl)# 20 permit ip host 10.3.3.3 any

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