Exit Zen
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../../principles/referencemodels.rst:54 • ../../principles/referencemodels.rst:65
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The Datalink layer
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../../principles/reliability.rst:51
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1 Kbps
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../../principles/transport.rst:33
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Alice : `Thank you`
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../../principles/sharing.rst:53
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A fifth physical organization of a network is the tree. Such networks are typically used when a large number of customers must be connected in a very cost-effective manner. Cable TV networks are often organized as trees.
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../../principles/security.rst:179
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As Mallory receives all the packets sent by both Bob and Alice, he can modify them at will. For example, he could modify the commands sent by Alice to the server managed by Bob and change the responses sent by the server. This type of attack is very powerful and sometimes difficult to counter without relying on advanced cryptographic techniques.
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../../exercises/dns.rst:43
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What are the nameservers that are responsible for the `info` top-level domain ? Is it possible to use IPv6 to query them ?
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../../exercises/http.rst:35
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curl_ supports a huge number of options and parameters that are described in its `man page <https://curl.haxx.se/docs/manpage.html>`_ Some of them allow you to force the utilization of a specific version of HTTP. These include `--http0.9`, `--http1.0`, `--http1.1` and `--http2`. Using the latter, verify whether your favorite website supports HTTP/2.0.
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../../exercises/ipv6.rst:42
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router ``R3`` uses address ``2001:db8:1341:34::3`` on its East interface, address ``2001:db8:1341:23::3`` on its North-East interface and address ``2001:db8:1341:13::3`` on its North interface
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../../exercises/lan.rst:85
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Consider the network depicted in Fig. 5. Both of the hosts `H0` and `H1` have two interfaces: one connected to the switch `S0` and the other one to the switch `S1`. Will the link between `S0` and `S1` ever be used? If so, under which assumptions? Provide a comprehensive answer.
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../../exercises/routing-policies.rst:143
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Consider that the AS stub (`AS456`) shown in the figure below decides to advertise two ``/48`` prefixes instead of its allocated ``/47`` prefix.
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../../exercises/routing-protocols.rst:186
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In its output, we see that ``r1`` is attached to two different routers. Finally, the ``show ipv6 ospf6 database`` returns the full OSPFv3 database with all the link state information that was distributed by OSPFv3.
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../../exercises/tcp-2.rst:65
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For this first example, we program packetdrill_ to inject the segments that a client would send. The first step is thus to prepare a :manpage:`socket` that can be used to accept this connection. This socket can be created by using the four system calls below.
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../../exercises/trace.rst:82
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wireshark_ is more recent than tcpdump_. It evolved from the ethereal packet trace analysis software. It can be used as a text tool like tcpdump_. For a TCP connection, wireshark_ can provide almost the same output as tcpdump_. The main advantage of wireshark_ is that it also includes a graphical user interface that allows performing various types of analysis on a packet trace.
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../../protocols/bgp.rst:53
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A simple Internet with peering relationships
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../../protocols/congestion.rst:46
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Most TCP implementations update the congestion window when they receive an acknowledgment. If we assume that the receiver acknowledges each received segment and the sender only sends MSS sized segments, the TCP congestion control scheme can be implemented using the simplified pseudo-code [#fwrap]_ below. This pseudocode includes the optimization proposed in :rfc:`3042` that allows a sender to send new unsent data upon reception of the first or second duplicate acknowledgment. The reception of each of these acknowledgment indicates that one segment has left the network and thus additional data can be sent without causing more congestion. Note that the congestion window is *not* increased upon reception of these first duplicate acknowledgments.
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../../protocols/dnssec.rst:158
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DNSSEC defines four new types of DNS records that are used together to authenticate the information distributed by the DNS.
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../../protocols/email.rst:63
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Email messages are entirely composed of lines of ASCII characters. Each line can contain up to 998 characters and is terminated by the `CR` and `LF` control characters :rfc:`5322`. The lines that compose the `header` appear before the message `body`. An empty line, containing only the `CR` and `LF` characters, marks the end of the `header`. This is illustrated in the figure below.
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../../protocols/ethernet.rst:89
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Ethernet 802.3 frame format
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../../protocols/http.rst:55
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Open standards play a key role in the success of the `world wide web` as we know it today. Without open standards, the world wide web would have never reached its current size. In addition to open standards, another important factor for the success of the web was the availability of open and efficient implementations of these standards. When CERN started to work on the `web`, their objective was to build a running system that could be used by physicists. They developed open-source implementations of the `first web servers <http://www.w3.org/Daemon/>`_ and `web clients <http://www.w3.org/Library/Activity.html>`_. These open-source implementations were powerful and could be used as is, by institutions willing to share information. They were also extended by other developers who contributed to new features. For example, the NCSA_ added support for images in their `Mosaic browser <http://en.wikipedia.org/wiki/Mosaic_(web_browser)>`_ that was eventually used to create `Netscape Communications <http://en.wikipedia.org/wiki/Netscape>`_ and the first commercial browsers and servers.
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../../protocols/http2.rst:70
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A closer look at the average web page shows that it contains, on average, 27 KBytes of HTML, 120 KBytes of fonts, 60 KBytes of CSS information, almost 1 MBytes of images and more than 400 KBytes of javascript. Each of these web page requires about 70 different HTTP requests. In other words, a browser needs to send on average 70 requests to retrieve a complete web page.
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