IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Organisation Remarks
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S 2.152 Design of a time synchronisation concept
Initiation responsibility: Head of IT Section, IT Security Management
Implementation responsibility: Administrators
The stability of a Netware 4.x network depends to great extent on the time
synchronisation and is closely related to the Novell Directory Services (NDS).
In this case, time synchronisation means that, in a network incorporating NDS
and containing several Netware servers, the clocks on these servers must
display the same time. The standard tolerance is two seconds. In other words,
the time deviation must not exceed two seconds between any of the clocks on
the Netware servers of the NDS. If this is ensured, the clock time in the
network is said to be synchronised.
In a multi-server network, several replications and/or partitions of the NDS are
generally distributed among the Netware servers. If one of the NDS partitions
is modified, it is supplied with a time stamp. During the next NDS
comparison, this modification is forwarded to the partitions and replications
on the other Netware servers in the network. If the clock on one of the
Netware servers which receives this modification is an hour behind and is
thereby not in sync, the changes for this NDS replication or partition can only
be synchronised when the affected server is in sync again.
In principle, a distinction can be made between the following two scenarios:
- Single reference model
This time model is recommended by Novell for networks with up to 30
Netware servers. It is very easy to configure, and does not require detailed
planning of the time synchronisation.
In this model, one single Netware server acts as the source of the clock
signal (single reference), while the remaining Netware servers only act as
signal recipients. The single-reference server indicates the time for the
entire network, and thus needs to be linked with an external time source
(e.g. a radio clock).
A major disadvantage of this time model is that a failure of the singlereference
server would lead to a lack of time synchronisation, as well as all
the resulting consequences.
- Time provider groups
In large networks, it is advisable to use time provider groups. These groups
are easy to configure but require appropriate planning. Several Netware
servers share the time server role. One of them is the reference server,
which should be connected to an external time source.
Primary time servers are located one level below the reference server; at
least two primary servers must exist in a network. There is hardly any
difference between this type of time server and a reference server.
Together, all reference and primary servers determine the valid network
time and pass on this time to the secondary servers. The reference server is
the stable factor in the network. As the reference server does not adjust its
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IT-Baseline Protection Manual: Oktober 2000