Term
| Explanation
|
configured
| This NTP clock source has been configured to be a server. This value can also be dynamic, where the peer/server was dynamically discovered.
|
our_master
| The local client is synchronized to this peer.
|
selected
| The peer/server is selected for possible synchronization, when 'our_master' fails or the client loses sync.
|
sane
| Sanity tests are used in order to test the NTP packet received from a server. These tests are specified in RFC 1305, Network Time Protocol (Version 3) Specification, Implementation and Analysis . The tests are:
Packet data is valid if tests 1 to 4 are passed. The data is then used in order to calculate offset, delay, and dispersion.
Packet header is valid if tests 5 to 8 are passed. Only packets with a valid header can be used to determine whether a peer can be selected for synchronization.
|
insane
| The sanity checks have failed, so time from the server is not accepted. The server is unsynced.
|
valid
| The peer/server time is valid. The local client accepts this time if this peer becomes the master.
|
invalid
| The peer/server time is invalid, and time will not be accepted.
|
ref ID
| Each peer/server is assigned a reference ID (label).
|
time
| Time is the last time stamp received from that peer/server.
|
our mode/ peer mode
| This is the state of the local client/peer.
|
our poll intvl/ peer poll intvl
| This is the poll interval from our poll to this peer or from the peer to the local machine.
|
root delay
| Root delay is the delay in milliseconds to the root of the NTP setup. Stratum 1 clocks are considered to be at the root of an NTP setup/design. In the example, all three servers can be the root because they are at stratum 1.
|
root dispersion
| Root dispersion is the maximum clock time difference that was ever observed between the local clock and the root clock. Refer to the explanation of 'disp' under the show ntp association section for more details.
|
sync dist.
| This is an estimate of the maximum difference between the time on the stratum 0 source and the time measured by the client; it consists of components for round trip time, system precision, and clock drift since the last actual read of the stratum source.
In a large NTP setup (NTP servers at stratum 1 in the internet, with servers that source time at different strata) with servers/clients at multiple strata, NTP synchronization topology should be organized in order to produce the highest accuracy, but must never be allowed to form a time sync loop. An additional factor is that each increment in stratum involves a potentially unreliable time server, which introduces additional measurement errors. The selection algorithm used in NTP uses a variant of the Bellman-Ford distributed routing algorithm in order to compute the minimum-weight spanning trees rooted on the primary servers. The distance metric used by the algorithm consists of the stratum plus the synchronization distance, which itself consists of the dispersion plus one-half the absolute delay. Thus, the synchronization path always takes the minimum number of servers to the root; ties are resolved on the basis of maximum error.
|
delay
| This is the round trip delay to peer.
|
precision
| This is the precision of the peer clock in Hz.
|
version
| This is the NTP version number used by the peer.
|
org time
| This is the time stamp of the NTP packet originator; in other words, it is this peer's time stamp when it created the NTP packet but before it sent the packet to the local client.
|
rcv time
| This is the time stamp when the local client received the message. The difference between org time and rcv time is the offset for this peer. In the example, master 10.4.2.254 has these times:
org time D36968B7.E74172BF (02:11:03.903 UTC Fri May 25 2012)
rcv time D36968B7.A2F44E2C (02:11:03.636 UTC Fri May 25 2012)
The difference is the offset of 268.3044 msec.
|
xmt time
| This is the transmit time stamp for the NTP packet the local client sends to this peer/server.
|
filtdelay
filtoffset
filterror
| This is the round trip delay in milliseconds of each sample.
This is the clock offset in milliseconds of each sample.
This is the approximate error of each sample.
A sample is the last NTP packet received. In the example, master 10.4.2.254 has these values:
filtdelay = 2.99 2.88 976.61 574.65 984.71 220.26 168.12 2.72
filtoffset = 268.30 172.15 -452.49 -253.59 -462.03 -81.98 -58.04 22.38
filterror = 0.02 0.99 1.95 1.97 2.00 2.01 2.03 2.04
These eight samples correspond to the value of the reach field, which shows whether the local client received the last eight NTP packets.
|
