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# Configuring NTP as a Multicast Client on a C Series Controller (SRC CLI)

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

You can specify one or more IP addresses or hostnames. The hosts then join those multicast groups.

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 multicast messages:

1. From the [edit system ntp] hierarchy level, specify that NTP listen for multicast messages.
   `
   edit system ntp]
   user@host# set multicast-client address
   `

   For example:

   `
   [edit system ntp]
   user@host# set multicast-client 224.0.1.1
   `
2. Authenticate time synchronization to ensure that the local system obtains its time only from known sources.

   See Configuring NTP Authentication on a C Series Controller (SRC CLI) .

3. Verify the configuration. For example:

       [edit system ntp]
       user@host# show
       multicast-client 224.0.1.1;
       trusted-key 1;
       server 192.0.2.30 key 1;
       authentication-key 1 {
         value ********;
       }

#### Related Topics

- Configuring NTP as a Multicast Client on a C Series Controller (C-Web Interface)
- Specifying Which NTP Server a C Series Controller Contacts on Startup
- NTP Support on C Series Controllers

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