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The Second Internet


Chapter 3 – Review of TCP/IPv4
This chapter is a brief review of TCP/IPv4, the foundation of the First Internet. Its purpose is to help you
understand what is new and different in TCP/IPv6. It is not intended to be comprehensive. There are
many great books listed in the bibliography if you wish to understand TCP/IPv4 at a deeper level. The
reason it is relevant is because the design of IPv6 is based heavily on that of IPv4. First, IPv4 can be
considered one of the great achievements in IT history, based on its worldwide success, so it was a good
model to copy from. Second, there were several attempts to do a new design “from the ground up” with
IPv6 (a “complete rewrite”). These involved really painful migration and interoperability issues. You
need to understand what the strengths and weaknesses of IPv4 are to see why IPv6 evolved the way it
did. You can think of IPv6 as “IPv4 on steroids”, which takes into account the radical differences in the
way we do networking today, and fixing problems that were encountered in the first 27 years of the
Internet, as network bandwidth and number of nodes increased exponentially. We are doing things over
networks today than no one could have foreseen a quarter of a century ago, no matter how visionary
they were.
3.1 – Network Hardware
There are many types of hardware devices used to construct an Ethernet network running TCP/IP
protocols. These include nodes, NICs, cables, hubs, switches, routers and firewalls.
A node (sometimes called a host) is a device (usually a computer) that can do processing and has some
kind of physical connection (wired or wireless) to a network. Examples of nodes are: desktop computers,
notebook computers, netbooks, smart phones, smart switches, routers, network printers, network
aware appliances, and so on. A node could be as simple as a temperature sensor, with no display and no
keyboard, just a connection to a network. It could possibly have a management interface accessed via
the network (e.g. with Telnet, SSH or web). All nodes on a network must have at least one IP address
(per interface). If a node has multiple interfaces connected to different networks, and the ability to
forward packets between them, then it is called a gateway. Routers and firewalls are special types of
gateways that can forward packets across networks and or control traffic in various ways. Gateways
make it possible to build internetworks. They are described in more detail under IPv4 Routing in this
chapter.
A NIC (or Network Interface Card) is the physical interface that connects a node to a network. It may also
be called an Ethernet adapter. It should have a female RJ-45 connector on it (or possibly coax or fiber
optic connector). It could be an actual add-in PCI card. It could be integrated on the device’s
motherboard. It could also be a something that makes a wireless connection to a network, using Wi-Fi,
WiMAX or other standard. Typically all NICs have a globally unique, hard-wired MAC address (48 bits
long, assigned by the manufacturer). A node can have one or more NICs (also called interfaces). Each
interface can be assigned one or more IP addresses, and various other relevant network configuration
items, such as the address of the default gateway and the addresses of the DNS servers.
Network cables today are typically unshielded twisted pair (UTP) cables that actually have four pairs of
plastic coated wires, with each pair forming a twisted coil. They have RJ-45 male connectors on each
end. They could also be fiber optic cables for very high speed or long run connections. Often today,
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