IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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In terms of their function, switches for ATM and Token-Ring are very similar
to Ethernet switches, i.e. a switch for these protocols also allows two network
subscribers or segments to communicate with each other, independently of the
remaining subscribers / segments. In fact, the underlying design of an ATM
network makes the use of switches mandatory in such a network.
During the selection of switches intended to realise a collapsed backbone, the
available port density must be taken into account. A collapsed backbone
should not involve the use of several switches, if these switches do not have a
common (high-speed) backplane (refer to S 5.2 Selection of an appropriate
network topography).
Routers
Routers separate or link networks on layer 3 of the OSI model. Routers thus
do not operate independent from network protocols (like repeaters and bridges
do, for example), but need to process the protocols in use on the network layer
too. As a result, routers significantly retard the flow of data between two
connected subnetworks, as they need to evaluate every packet on layer 3.
Due to their ability to process protocols, routers are used mainly for LAN-
LAN and LAN-WAN coupling. For example, a router can link two LANs via
an ISDN line. In this case, the LAN protocol is encapsulated in its original
form in the WAN protocol and then transferred. Another protocol which can
be used here is the X.25 protocol. In large networks consisting of many
subnetworks which are linked together via routers, one important task
performed by these routers is routing between the subnetworks, i.e.
forwarding of data packets between these subnetworks. A fundamental
distinction can be made between two techniques here:
- Static routing, which involves manual specification of routes.
- Dynamic routing, which involves automatic discovery and regular updating
of routes by the router. For this purpose, several algorithms and protocols
are available which also ensure synchronisation between the individual
routers. The most familiar protocols are RIP (Routing Information
Protocol), OSPF (Open Shortest Path First) and IGRP (Interior Gateway
Routing Protocol). For the selection of a suitable routing protocol, also
refer to S 4.82 Secure configuration of active network components.
Filters can also be used to ensure access control, i.e. to specify which systems
are allowed to communicate with each other via the router in which directions
using which protocols.
Concentrators and hubs
A Hub is an element which incorporates one or more active network coupling
components and allows these components to communicate with each other via
an internal backplane (also refer to S 5.2 Selection of an appropriate network
topography). Hubs which can incorporate several network coupling
components, if required, are termed modular hubs. Accordingly, hubs which
can only incorporate one coupling component are termed non-modular hubs.
If it is possible to connect the backplanes of several hubs together, these hubs
are termed stackable hubs. The use of a hub or concentrator results - at least to
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IT-Baseline Protection Manual: Oktober 2000