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IT Baseline Protection Manual - The Information Warfare Site

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Safeguard Catalogue - Hardware & Software Remarks<br />

____________________________________________________________________ .........................................<br />

S 4.62 Use of a D-channel filter<br />

Initiation responsibility: Head of <strong>IT</strong> Section, <strong>IT</strong> Security Management<br />

Implementation responsibility: Administrator, Purchase Department<br />

A D-channel filter is installed between the ISDN connection (S2M or S0) and<br />

the ISDN terminal device or ISDN private branch exchange (PBX). This filter<br />

acts as an ISDN terminal device facing the ISDN connection, and as an ISDN<br />

connection facing the ISDN terminal device. <strong>The</strong> D-channel filter monitors<br />

the ISDN D-channel for impermissible protocol actions and is thus capable of<br />

detecting, as well as preventing, attempts at manipulation via the D-channel.<br />

Use of a D-channel filter is particularly advisable in situations where<br />

unauthorised access by qualified persons via remote access ports is<br />

conceivable (for example, during remote maintenance and administration).<br />

A D-channel filter also restricts performance features and services for the call<br />

numbers of certain communications partners so as to prevent the ISDN<br />

terminal device from being misused and endangered under certain operational<br />

conditions. A D-channel filter responds to an unauthorised attempt to make<br />

use of performance features and services by closing down the connection<br />

(disconnect, release) and logging the attempt.<br />

Further details on this technology - which was initiated by the BSI - can be<br />

obtained from the <strong>IT</strong> baseline protection hotline.<br />

____________________________________________________________________ .........................................<br />

<strong>IT</strong>-<strong>Baseline</strong> <strong>Protection</strong> <strong>Manual</strong>: Oktober 2000

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