Exit Zen
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../../protocols/tcp.rst:9
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The Transmission Control Protocol
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../../protocols/tls.rst:7
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Transport Layer Security
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../../protocols/udp.rst:9
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The User Datagram Protocol
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../../bibliography.rst:7
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Whenever possible, the bibliography includes stable hypertext links to the references cited.
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../../principles/security.rst:10
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In the early days, data networks were mainly used by researchers and security was not a concern. A few users were connected and capable of using the network. Almost all the devices attached to the network were openly accessible and users were trusted. As the utilization of the networks grew, security concerns started to appear. In universities, researchers and professors did not always trust their students and required some forms of access control. On standalone computers, the common access control mechanism is the password. A `username` is assigned to each user and when this user wants to access the computer, he or she needs to provide his/her `username` and his/her `password`. Most passwords are composed of a sequence of characters. The strength of the password is function of the difficulty of guessing the characters chosen by each user. Various guidelines have been defined on how to select a good password [#fpasswords]_. Some systems require regular modifications of the passwords chosen by their users.
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../../exercises/dns.rst:11
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This is an unpolished draft of the third edition of this e-book. If you find any error or have suggestions to improve the text, please create an issue via https://github.com/CNP3/ebook/issues?milestone=5 or help us by providing pull requests to close the existing issues.
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../../exercises/email.rst:7
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Many Internet protocols are ASCII_-based protocols where the client sends requests as one line of ASCII_ text terminated by `CRLF` and the server replies with one of more lines of ASCII_ text. Using such ASCII_ messages has several advantages compared to protocols that rely on binary encoded messages
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../../exercises/http.rst:8
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An important difference between HTTP/1.0, HTTP/1.1 and HTTP/2.0 is their utilization of the underlying transport connections. Answer the three questions below to confirm that you understand the difference between these versions of the HTTP protocol.
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../../exercises/ipv6.rst:9
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Basic questions on IPv6 Networks
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../../exercises/lan.rst:18
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Exercises
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../../exercises/routing-policies.rst:9
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Exercises
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../../exercises/routing-protocols.rst:9
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Routing protocols play a key role in the Internet since they ensure that all the routers have valid routing tables. In this section, we use IPMininet_ to explore how intradomain and interdomain routing protocols work in practice. IPMininet_ adds an abstraction layer above the actual configuration of the FRRouting daemons that implement these routing protocols.
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../../exercises/tcp-2.rst:10
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In this series of exercises, you will explore in more details the operation of TCP and its congestion control scheme. TCP is a very important protocol in today's Internet since most applications use it to exchange data. We first look at TCP in more details by injecting segments in the Linux TCP stack and analyze how the stack reacts. Then we study the TCP congestion control scheme.
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../../exercises/tcp.rst:9
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TCP is one of the key protocols in today's Internet. A TCP connection always starts with a three-way handshake. The exercises below should help you to improve your understandings of this first phase of a TCP connection.
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../../exercises/tls.rst:8
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One of the first motivations for the deployment of wide area networks such as the Internet was to enable researchers to connect to distant servers. For many years, these connections were carried out by using a simple application layer protocol such as telnet over a TCP connection. With telnet, all the characters typed by the user are sent in cleartext over the TCP connection. This implies that if someone is able to capture the packets transmitted over the network, he/she can collect sensitive information such as user names or passwords.
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../../exercises/trace.rst:8
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When debugging networking problems or to figure out performance problems, it is sometimes useful to capture the segments that are exchanged between two hosts and to analyze them.
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../../protocols/bgp.rst:7
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As explained earlier, the Internet is composed of more than 45,000 different networks [#fasnum]_ called `domains`. Each domain is composed of a group of routers and hosts that are managed by the same organization. Example domains include belnet_, sprint_, level3_, geant_, abilene_, cisco_ or google_ ...
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../../protocols/congestion.rst:11
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In an internetwork, i.e. a networking composed of different types of networks (such as the Internet), congestion control could be implemented either in the network layer or the transport layer. The congestion problem was clearly identified in the later 1980s and the researchers who developed techniques to solve the problem opted for a solution in the transport layer. Adding congestion control to the transport layer makes sense since this layer provides a reliable data transfer and avoiding congestion is a factor in this reliable delivery. The transport layer already deals with heterogeneous networks thanks to its `self-clocking` property that we have already described. In this section, we explain how congestion control has been added to TCP and how this mechanism could be improved in the future.
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../../protocols/dnssec.rst:9
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The Domain Name System provides a critical service in the Internet infrastructure since it maps the domain names that are used by end users onto IP addresses. Since end users rely on names to identify the servers that they connect to, any incorrect information distributed by the DNS would direct end users' connections to invalid destinations. Unfortunately, several attacks of this kind occurred in the past. A detailed analysis of the security threats against the DNS appeared in :rfc:`3833`. We consider three of these threats in this section and leave the others to :rfc:`3833`.
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../../protocols/ethernet.rst:12
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Ethernet was designed in the 1970s at the Palo Alto Research Center [Metcalfe1976]_. The first prototype [#fethernethistory]_ used a coaxial cable as the shared medium and 3 Mbps of bandwidth. Ethernet was improved during the late 1970s and in the 1980s, Digital Equipment, Intel and Xerox published the first official Ethernet specification [DIX]_. This specification defines several important parameters for Ethernet networks. The first decision was to standardize the commercial Ethernet at 10 Mbps. The second decision was the duration of the `slot time`. In Ethernet, a long `slot time` enables networks to span a long distance but forces the host to use a larger minimum frame size. The compromise was a `slot time` of 51.2 microseconds, which corresponds to a minimum frame size of 64 bytes.
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