What is Network Time Protocol?

Transcription

1 to October 25, 2008 to 1 to 2 3 What is? to According to RFC 1305, the (NTP) used to synchronizes the time among the network devices such as routers, servers and clients to some time reference. NTP applies on UDP port 123 and implement to Application Layer. The basic idea of using NTP is that the network applications need to have time synchronized over the Internet or the LAN while log information and debugging information collected from different devices in network management, time must be used as reference basis.

2 What is? to Netowork Time also: Developed by Professor David Mills (who still maintains it) from the University of Delaware and is still in use since 1985 There were developed a lot of versions such as NTP version 1, version 2 and version 3. NTP version 4 is in use but NTPv3 is the offcial Internet standard and NTP version 5 is developed Brief of NTP to 1980: Started NTP implementations described in Internet Engineering Note (IEN-173). The first RFC was introduced in [RFC 778] called Internet Clock Service. NTP was appeared in [RFC 958] 1988: NTP version 1 was introduced in [RFC 1059] 1989: NTP version 2 was appeared and described in [RFC 1119]. The same period another time synchronization protocol was introduced by Digital Equipment Corporation called Digital Time Synchronization Service (DTSS) 1992: A combination of DTSS and NTP produced NTP version 3, [RFC 1305] 1994: A new version was in progress, Simple (SNTP) version 4 for IPv4, IPv6 and OSI described in [RFC 2030] How does NTP work? to NTP operates as a primary server, secondary server or client: A primary server synchronizes directly to a reference clock such as GPS receiver which is synchronized with the Coordinated Universal Time (UTC, standard solar time) Clients are synchronized by the servers but do not provide synchronization to other systems A secondary server has upstream and downstream servers or clients NTP clients can work with NTP servers in three ways: 1 In a client-server mode 2 In a peer to peer mode 3 Transfer the time using broadcast/multicast

3 Strata System 1/2 to Figure: Strata System with Stratum Levels. Image retrieved from http : //en.wikipedia.org/wiki/network Time Strata System 2/2 to The hierarchical system of Stratum Levels. The levels describe the distance from the source clock: Stratum-0: Reference Clock, GPS receiver, atomic clocks, synchronized to UTC Stratum-1: Computer servers connected with Stratum-0 devices to serve and synchronize other computers in Stratum-2, 3 etc. via NTP Stratum-2: Computers that request time from Stratum-1 servers via NTP. Stratum-2 computers communicate with other Stratum-2 in peer mode to provide steady and accurate time. Furthermore, Stratum-2 operate as server to Stratum-2 computers Stratum-3: Do the same as Stratum-2 and provide time to next Stratum. NTP can handle 16 levels of Stratum How is Time Synchronized? 1/3 to Figure:. Image retrieved from http : // NTP pdf

4 How is Time Synchronized? 2/3 to Conditions: The clock of Device A is 10:00:00 am and the clock of Device B is to 11:00:00 am. Device A requests a synchronization from Device B which is a time server NTP needs 1 sec to transfer the message between the two devices How is Time Synchronized? 3/3 to Now the Device A can calculate the round trip delay and offset parameters and synchronize its own time to Device B time: Round trip delay : Delay = (T4-T1) - (T3-T2) = 2 seconds Time difference between Device A and Device B: Offset = ((T2-T1) + (T3-T4))/2 = 1 hour. Format to The NTP timestamp format include 64 bit binary unsigned value 32 bits used for the seconds and 32 bits used for fractions of second (233 picoseconds) NTP uses an epoch of January 1, 1900 UTC, when all bits are zero Time scale of 2 32 seconds (136 years) The protocol is well precise, with less than a nanosecond (2 32 seconds).

5 NTP Data Packet Structure 1/2 to Figure: NTP Data Packet Structure. Image retrieved from http : // NTP Data Packet Structure 2/2 to Mode: 0 : Reserved 1 : Symmetric active 3 : Client 4 : Server 5 : Broadcast 6 : NTP control message Stratum: The stratum level Root Delay: The total roudn trip delay in seconds from reference source Originate Timestamp: The time that client sends the request to server Receive Timestamp: The time that message received from the server Transmit Timestamp: The time which the reply message left the server for the client 1/2 to Figure: ntpq. Image retrieved from http : //networking.ringofsaturn.com/s/ntp.php Remote: The first 15 characters for the servers name Refid: Servers source for time. If it is you can t receive time St: Servers stratum level. If it is 16 or above you can t receive time t: u: unicast, b: broadcast, l: local When: Is the number of seconds since a server received the message

6 2/2 to Delay: The number of milliseconds that it is taking for NTP packets to make the rtt from the client, server and back. This is an important parameter used by NTP to choose the valuable server. Offset: Is the difference in milliseconds between the time in your client and the remote server. Jitter: Is number of milliseconds of successive packets send through the network. It is evaluate the stability of the network path to the remote server Summary to NTP, is a protocol that synchronize the time between the network devices The last version that developed was v4 The clients request time synchronization from the servers through NTP. The clients can also synhcronize the time in a peer to peer mode Strata System. Stratum-0 is the reference time device like GPS receiver The NTP timestamp format is 64 bit binary unsigned value. The first date is 01/01/1900. Next wrap at 136 years NTP with the program ntpq Resources 1 to http : // project http : // NTP pdf http : //networking.ringofsaturn.com/s/ntp.php Wikipedia: http : //en.wikipedia.org/wiki/network Time

7 Resources 2 to Akadia: http : // synchronize.html Version 4 Reference and Implementation Guide, David L. Mills University of Delaware, June 2006 : http : // mills/database/reports/ntp4/ntp4.pdf RFC1305, (Version 3) Specification, Implementation and Analysis, David L. Mills, 1992 http : //