Refusing Broadcasts from NTP Servers

You can prevent the system from receiving certain types of broadcasts and specify the servers from which the system will accept NTP broadcasts. To do so:

1. Issue the ntp access-group command.
2. Configure an access list.

access-list

• Use to configure an access list.
• Example

  host1(config)#access-list europe permit any

• Use the no version to remove the access list.
• See access-list.

ntp access-group

Note: The system can accept, but does not use, NTP control queries.

• Use to specify the types of broadcasts that the system will accept and respond to, and to specify an access list of servers from which the system will accept broadcasts.You can enable the system to:
  • Receive time requests, receive NTP control queries, and synchronize itself to the servers specified on the access-list
  • Only receive time requests and NTP control queries from specified servers
  • Only receive time requests from specified servers
  • Only receive NTP control queries from specified servers
• Example

  host1(config-line)#ntp access-group peer europe

• Use the no version to enable the system to receive all NTP broadcasts on interfaces configured to receive broadcasts.
• See ntp access-group.

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