TCP/IP. This section examines the TCP, UDP, ICMP, and ARP protocols in detail. TCP and
UDP are the two transport layer (Layer 4) protocols most often used by applications in a
TCP/IP network. ICMP and ARP are actually parts of the network layer (Layer 3) of TCP/IP
and are used in conjunction with IP. As you'll see on the exam, IP addressing is something that
all CCNAs must master to confidently pass the exam. Due to the importance of IP, IP addressing
will be covered in great detail in the next section of this chapter.
route might match the packet, or there may not be enough buffer space in the router to store
the packet until the next link is available. Layer 3 protocols do not typically provide for
retransmission; a typical commentary is, "That's done by some higher-layer protocol."
error recovery--namely, the Transmission Control Protocol (TCP). Defined in RFC 793, TCP
performs error recovery as well as other features, including these:
end-to-end deliveries of the data, including routing issues. In other words, TCP performs only
part of the functions necessary to deliver the data between applications.
but several fields will be referred to in this section. The Internetworking Technologies
Multimedia (ITM) CD, which is a suggested prerequisite for the exam, lists the fields with a
brief explanation, as does the Cisco Press book on which ITM is based: