Foundry NetIron M2404C and M2404F Metro Access Switches
Switch Administration (Rev. 03)
Managing the System Time and Date © 2008 Foundry Networks, Inc.
Page 64 of 87
Managing the System Time and Date
Network Time Protocol (NTP) is a protocol that provides a reliable way of transmitting and
receiving the time over IP network such as the Internet or a corporate local area network. Network
Time Protocol, present virtually on all computers, allows systems to synchronize their clocks with
a time source over the IP networks.
Overview
Network Time Protocol
The NTP is designed to synchronize clocks among devices in a network. NTP runs over User
Datagram Protocol (UDP), which runs over IP. An NTP network usually gets its time from an
authoritative time source, such as a radio clock or an atomic clock attached to a time server. NTP
then distributes this time across the network. NTP is extremely efficient; no more than one packet
per minute is necessary to synchronize two devices within a millisecond of each other.
NTP is a tiered time distribution system with redundancy capability. NTP measures delays within
the network and within the algorithms on the machine on which it is running. Using these tools and
techniques, it is able to synchronize clocks to within milliseconds of each other when connected on
a Local Area Network and within hundreds of milliseconds of each other when connected to a
Wide Area Network. The tiered nature of the NTP time distribution tree enables a user to choose
the accuracy needed by selecting a level (stratum) within the tree for machine placement. A time
server placed higher in the tree (lower stratum number), provides a higher likelihood of agreement
with the UTC time standard.
You should use the security features of NTP to avoid the accidental or malicious setting of an
incorrect time by using an encrypted authentication mechanism.
Daytime Protocol
The daytime service is a useful debugging and measurement tool. A daytime service simply sends
the current date and time without regard to the input.
TCP Based Daytime Service
One daytime service is defined as a connection-based application on TCP. A server listens for TCP
connections on TCP port 13. Once a connection is established the current date and time is sent out
the connection as an ASCII character string (and any data received is thrown away). The service
closes the connection after sending the quote.
UDP Based Daytime Service
Another daytime service is defined as a datagram-based application on UDP. A server listens for
UDP datagrams on UDP port 13. When a datagram is received, an answering datagram is sent
containing the current date and time as an ASCII character string (the data in the received datagram
is ignored).
Time Protocol
This protocol provides a site-independent, machine readable date and time. The Time service sends
back to the originating source the time in seconds since midnight, January first 1900.
One motivation arises from the fact that not all systems have a date/time clock, and that all are
subject to occasional human or machine error. The use of time-servers makes it possible to quickly