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8.8
Leap second
The announcement of the switching second is put out by DCF and NTP* each time 1
hour before the defined time.
*The announcement is only sent via NTP if a DCF source is active. If only one NTP
source is configured, the state of this source is passed on.
Automatic mode
In the automatic mode, the source (DCF or NTP) is checked for a possible
announcement during 1 hour prior to the moment of a possible leap second. If the
announcement is recognized, it is passed through the NTP and DCF outputs and the
leap second is inserted.
The leap second can be inserted at 2 moments per year: 00:00:00 1.1. or 00:00:00 1.7.
each in UTC. Whether a leap second is inserted is decided by the organization IERS
(http://www.iers.org) each time up to half a year in advance.
8.9
NTP Authentication
NTP provides two variants for authentication in version 4:
•
NTP symmetric keys (i.e. symmetric keys)
•
NTP autokeys
NTP authentication assures a correct time source and prevents manipulation of NTP
information. NTP data itself is, however, not encoded.
8.9.1
NTP symmetric keys
A 32-bit key ID and a cryptographic 64/128-bit check sum of the packet is attached to
each NTP IP packet.
The following algorithms are used for this purpose:
•
Data Encryption Standard (DES)
(partly restricted in North America and no longer integrated into new NTP variants
(>V4.2))
•
Message Digest (MD5)
The DTS 4132 only supports the MD5 procedure.
The receiving NTP service calculates the check sum with an algorithm and compares it
with the one contained in the packet. Both NTP services must have the same
encryption key and the same corresponding key ID for this purpose.
Packets with a wrong key or wrong check sum will not be used for synchronization .
The DTS 4132 must be correspondingly configured to be able to use NTP
authentication (chapter 6.5.14 NTP server). The NTP service of the other equipment
(e.g. server, PC...) must also be configured. In the case of standard NTP, this occurs
via the ntp.conf file:
# path for key file
keys /etc/ntp/ntp.keys
trustedkey 1 2 3 4 5 6# define trusted keys
requestkey 4 # key (7) for accessing server variables
controlkey 5 # key (6) for accessing server variables
server ntp1.test.org key 2
server ntp2.test.org key 6
server 192.168.23.5 key 3
