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Router Security Configuration Guide
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Version 1.0g
OSI model. A collection of various compatible protocol layers is referred to as a
stack.
Figure 2-1: Network Layers and Standards
Routing occurs at layer three, the Network Layer. To fully understand routing it is
useful to appreciate some of what goes on beneath it at the Data Link Layer, and
some of this is discussed in the following sections. However, the Physical Layer is at
a level of detail well below the concerns of this document. It is concerned with the
transmission of an unstructured bit stream over a physical link. This involves such
details as signal voltage and duration; or optical signaling details for fiber. It also
covers the mechanical aspects of connectors and cables. It may also cover some low
level error control.
Application
Presentation
Session
Transport
Network
Data Link
Physical
ISO/OSI Model
Application
Transport
Network
TCP/IP Model
Logical Link Control
Media Access Control
Physical
IEEE Standards
802.1
802.2
802.3
(Ethernet){
TCP or UDP
IP
7
6
5
4
3
2
1
Layer
Data link
