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Background and Review
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2.5. Review of Router-Relevant Protocols and Layers
The following sections are not inclusive of all protocols that might be of interest but
are representative. For more details see Section 4.4, “Routing and Routing
Protocols”. The protocols are grouped according the OSI layer to which they
correspond.
2.5.1. Physical Layer 1
As previously discussed, the physical layer defined by IEEE or similar standards that
define what are primarily hardware characteristics.
2.5.2. Data Link Layer 2
The IEEE and other standards that apply at this layer have also been discussed
previously.
2.5.3. Network Layer 3
IP – the Internet Protocol (IP) provides a specification for packet formatting and an
unreliable, connectionless, best effort delivery of those packets.
ARP – Hosts use the Address Resolution Protocol (ARP) to acquire the MAC address
of other hosts.
2.5.4. Transport Layer 4
TCP – the Transmission Control Protocol (TCP) is a connection-oriented, reliable
protocol. Before transmitting data a connection must be established and after data
transmission is complete the connection must be closed.
UDP – the User Datagram Protocol (UDP) is a connectionless, best effort protocol
with no guarantee of delivery or confirmation of delivery. It has lower overhead than
TCP. When we speak of TCP/IP we are usually implicitly including UDP.
ICMP – the Internet Control Message Protocol (ICMP) provides the mechanisms for
hosts and routers to report network conditions and errors to other hosts and routers.
(For example, the ping command relies on ICMP.)
OSPF – Open Shortest Path First is a relatively complex, fast-converging routing
protocol. It is an interior gateway protocol that uses a link state routing algorithm and
requires that a hierarchy of areas be designed. An area is a logical collection of
routers and networks.
RIP – Routing Information Protocol is a dynamic routing protocol that allows routers
to share network information with each other. It is a distance vector protocol that