Exit Zen
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../../protocols/email.rst:98
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The email header contains several lines that all begin with a keyword followed by a colon and additional information. The format of email messages and the different types of header lines are defined in :rfc:`5322`. Two of these header lines are mandatory and must appear in all email messages :
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../../protocols/ethernet.rst:92
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What is the Ethernet service ?
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../../protocols/http.rst:58
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The first components of the `world wide web` are the Uniform Resource Identifiers (URI), defined in :rfc:`3986`. A URI is a character string that unambiguously identifies a resource on the world wide web. Here is a subset of the BNF for URIs ::
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../../protocols/ipv6.rst:90
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PIP proposed in :rfc:`1621`
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../../protocols/ppp.rst:35
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`LAPB <http://en.wikipedia.org/wiki/LAPB>`_ and `HDLC <http://en.wikipedia.org/wiki/HDLC>`_ were widely used datalink layer protocols.
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../../protocols/rpc.rst:36
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For basic data types, :rfc:`1832` simply maps their representation into a sequence of bytes. For example a 32 bits integer is transmitted as follows (with the most significant byte first, which corresponds to big-endian encoding).
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../../protocols/ssh.rst:121
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This negotiation of the cryptographic algorithms allows the implementations to evolve when new algorithms are proposed. If a client is upgraded, it can announce a new algorithm as its preferred one even if the server is not yet upgraded.
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../../protocols/tcp.rst:39
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the address of the client
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../../protocols/tls.rst:44
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993
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../../protocols/transport-service.rst:49
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It is sometimes necessary to write IPv6 addresses in text format, e.g. when manually configuring addresses or for documentation purposes. The preferred format for writing IPv6 addresses is `x:x:x:x:x:x:x:x`, where the `x` 's are hexadecimal digits representing the eight 16-bit parts of the address. Here are a few examples of IPv6 addresses :
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../../protocols/udp.rst:56
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a 16 bits checksum
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../../protocols/wifi.rst:22
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2 Mbps
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../../bibliography.rst:51
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Cohen, D., `On Holy Wars and a Plea for Peace`, IEN 137, April 1980, http://www.ietf.org/rfc/ien/ien137.txt
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../../glossary.rst:14
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The American Standard Code for Information Interchange (ASCII) is a character-encoding scheme that defines a binary representation for characters. The ASCII table contains both printable characters and control characters. ASCII characters were encoded in 7 bits and only contained the characters required to write text in English. Other character sets such as Unicode have been developed later to support all written languages.
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../../exercises/ex-sharing.rst:316
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An important part of the CSMA/CD algorithm is the exponential backoff. To illustrate the operation of this algorithm, let us consider a cable that has a length of one kilometer. The bandwidth of the network is set to 10 Mbps. Assume that when a collision occurs, host A always selects the highest possible random delay according to the exponential backoff algorithm while host B always selects the shortest one. In this network, the slot time is equal to the time required to transmit 100 bits. We further assume that a host can detect collision immediately (i.e. as soon as the other frame arrives).
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../../principles/transport.rst:41
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Such a conversation succeeds if both Alice and Bob speak the same language. If Alice meets Tchang who only speaks Chinese, she won't be able to ask him the current time. A conversation between humans can be more complex. For example, assume that Bob is a security guard whose duty is to only allow trusted secret agents to enter a meeting room. If all agents know a secret password, the conversation between Bob and Trudy could be as follows :
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../../principles/sharing.rst:62
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Sharing bandwidth
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../../principles/security.rst:198
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In practice, there is a possibility of denial of service attacks as soon as there is a limited resource somewhere in the network. This resource can be the bandwidth of a link, but it could also be the computational power of a server, its memory or even the size of tables used by a given protocol implementation. Defending against real DoS attacks can be difficult, especially if the attacker controls a large number of sources that are used to launch the attacks. In terms of bandwidth, DoS attacks composed of a few Gbps to a few tens of Gbps of traffic are frequent on the Internet. In 2015, `github.com <http://www.github.com>`_ suffered from a distributed DoS that reached a top bandwidth of 400 Gbps according to some `reports <http://www.techworld.com/news/security/worlds-largest-ddos-attack-reached-400gbps-says-arbor-networks-3595715/>`_.
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../../exercises/dns.rst:48
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When run without any parameter, `dig` queries one of the root DNS servers and retrieves the list of the names of all root DNS servers. For technical reasons, there are only 13 different root DNS servers. This information is also available as a text file from http://www.internic.net/zones/named.root. What are the IPv6 addresses of all these servers?
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../../exercises/ipv6.rst:45
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The forwarding paths used in a network depend on the forwarding tables installed in the network nodes. Sometimes, these forwarding tables must be configured manually.
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