When the NTP server or peer is configured with burst mode, client will send burst of up to 8 NTP
packets in each polling interval. The burst number of packets in each interval increases as the polling
interval increases from minimum polling interval towards maximum interval.
The NTP peer can operate in:
• Symmetric Active-When the peer is configured using the peer command.
• Symmetric Passive-Dynamically learned upon arrival of a NTP packet from the peer which is not
configured. The symmetric passive association is removed on timeout or error.
The following scenarios are observed when the upstream server is not reachable after retries:
• If the NTP server/peer is configured and the master command is not configured, then the system
clock is synchronized. When the system clock is synchronized, the server will respond to client's
request with the stratum number set to +1. And when the system clock is unsynchronized, the
server will respond to client's request with the stratum number set to 16.
• If the NTP server/peer is configured and the master command is configured, then the system clock
is synchronized. When the system clock is synchronized, the reference time is the local clock time.
If the local clock is valid then the server will respond to client's request with the specified stratum
number if it is configured otherwise with the default stratum number.
The following scenarios are observed when you remove the last NTP server/peer under the conditions
- the NTP server/peer is configured, master command is not configured, system clock is synchronized
and the reference time is the NTP time:
• If the local clock is not valid, the system clock is not synchronized.
• If the local clock is valid, the system clock is synchronized and the reference time is the local clock.
The server will respond to the client's request with the specified stratum number if it is configured
otherwise with the default stratum number.
NOTE
To create a symmetric active association when a passive association is already formed, disable NTP,
configure peer association and then enable NTP again.
NTP broadcast server
An NTP server can also operate in a broadcast mode. Broadcast servers send periodic time updates
to a broadcast address, while multicast servers send periodic updates to a multicast address. Using
broadcast packets can greatly reduce the NTP traffic on a network, especially for a network with many
NTP clients.
The interfaces should be enabled with NTP broadcasting. The NTP broadcast server broadcasts the
NTP packets periodically (every 64 sec) to subnet broadcast IP address of the configured interface.
• NTP broadcast packets are sent to the configured subnet when the NTP broadcast server is
configured on the interface which is up and the IP address is configured for the broadcast subnet
under the following conditions:
‐ The local clock is valid and the system clock is synchronized
‐ The local clock is valid and the system clock is not synchronized
‐ Authentication key is configured, the system clock is synchronized and the local clock is
valid
• NTP broadcast packets are not sent in the following cases:
NTP broadcast server
40 FastIron Ethernet Switch Administration Guide
53-1003625-01
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