IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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S 5.75 Protecting against overloading the fax server
Initiation responsibility: Head of IT Section, IT Security Management
Implementation responsibility: Administrator, fax mail centre
A fax server can become overloaded with either incoming or outgoing fax
transmissions. If the fax server is overloaded, this could mean that no further
fax transmissions can be received or sent for the time being. It is also possible
that overloading of the fax server could cause the operating system or the fax
server application to crash so that the fax server is temporarily completely
unavailable.
The fax server can be said to be overloaded if all the channels available
through the communications cards are blocked with incoming and outgoing
fax transmissions. The result is that no more faxes can be received or sent
until a channel becomes free again. If all the lines provided by the
telecommunications company are busy with incoming and outgoing fax
transmissions, this has the same result.
Before purchasing one or more fax servers the likely volume of faxes should
be estimated. Components which are capable of handling this volume should
then be purchased. Care should also be taken to ensure that sufficient
telecommunications lines are available.
The fax server log files should be regularly examined so that if there are
certain times when the server is overloaded or is functioning at the limits of its
capacity, these can be identified.
Overloading of the fax server can occur if an attempt is made to send out a
large number of faxes from within the organisation. Under unfavourable
conditions, this could cause the fax server application or the operating system
to crash. This could be triggered, for example, by an attempt to send out a
large number of serial faxes. During the test or pilot phase, tests should
therefore be run so as to determine the loading limits. To avoid exceeding
these limits, a maximum size should be imposed on users for serial fax
transmissions, e.g. through an appropriate standard operating procedure
(SOP). Very large serial fax transmissions should then be split into several
smaller transmissions. At times when the fax server is heavily loaded, steps
should be taken to ensure that faxes are only sent in urgent cases. This can be
achieved either using an appropriate SOP or by appropriate permission
settings on the fax server. One possible solution is to stipulate that where
possible faxes are only to be sent after working hours, which also has the
advantage of lower telephone charges.
If it is established that the fax server is always blocked at certain times by the
same originating numbers sending large numbers of faxes, first of all the
identity of the originators and the nature of the fax transmissions concerned
should be established. If the organisation really needs these faxes, one
possibility is to negotiate times with the originators at which they should send
their faxes so that they can be received without any problems. If the faxes are
not actually needed (e.g. unsolicited advertising material), an attempt can be
made to block these originator numbers via the fax server application or else
via the private branch exchange. However, this is only possible if the
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IT-Baseline Protection Manual: Oktober 2000
Procurement of suitable
components
Delayed transmission
Agreement with the
originator