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Configuring NTP to Listen for Broadcast Messages

You can configure NTP on a C-series platform to listen for broadcast messages on the local network to discover other servers on the same subnet. When NTP receives a broadcast message for the first time, it measures the nominal network delay using a brief client-server exchange with the remote server. It then enters broadcast client mode, in which it listens for, and synchronizes to, succeeding broadcast messages.

To avoid accidental or malicious disruption in this mode, both the local and remote systems must use authentication and the same trusted key and key identifier.

To configure NTP to listen for broadcast messages:

  1. From the [edit system ntp] hierarch level, specify that NTP listen for broadcast messages.
  2. [edit system ntp]
    
    user@host# set broadcast-client 
    
    
    
  3. Authenticate time synchronization to ensure that the local system obtains its time only from known sources.

See Configuring NTP Authentication.

  1. Verify the configuration. For example:
  2. [edit system ntp]
    
    user@host# show
    
    broadcast-client;
    
    trusted-key 1;
    
    server 192.0.2.30 key 1;
    
    authentication-key 1 {
    
      value ********;
    
    }
    
    
    

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