Exit Zen
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../../protocols/tcp.rst:40
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the address of the server
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../../protocols/tls.rst:45
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NNTP
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../../protocols/transport-service.rst:51
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`abcd:ef01:2345:6789:abcd:ef01:2345:6789`
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../../protocols/udp.rst:58
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As the port numbers are encoded as a 16 bits field, there can be up to only 65535 different server processes that are bound to a different UDP port at the same time on a given server. In practice, this limit is never reached. However, it is worth noticing that most implementations divide the range of allowed UDP port numbers into three different ranges :
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../../protocols/wifi.rst:22
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../../bibliography.rst:52
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Donahoo, M., Calvert, K., `TCP/IP Sockets in C: Practical Guide for Programmers <http://books.google.com/books?id=dmt_mERzxV4C>`_ , Morgan Kaufman, 2009
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../../glossary.rst:99
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ASN.1
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../../exercises/ex-sharing.rst:343
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Fairness and congestion control
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../../exercises/reliability.rst:36
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there are no transmission errors
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../../exercises/sockets.rst:139
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Receiving data from a peer using a socket
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../../exercises/transport.rst:135
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Discussion questions
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../../principles/naming.rst:82
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This hierarchical naming scheme is a key component of the Domain Name System (DNS). The DNS is a distributed database that contains mappings between fully qualified domain names and addresses. The DNS uses the client-server model. The clients are hosts or applications that need to retrieve the mapping for a given name. Each :term:`nameserver` stores part of the distributed database and answers the queries sent by clients. There is at least one :term:`nameserver` that is responsible for each domain. In the figure below, domains are represented by circles and there are three hosts inside domain `dom` (`h1`, `h2` and `h3`) and three hosts inside domain `a.sdom1.dom`. As shown in the figure below, a sub-domain may contain both host names and sub-domains.
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../../principles/referencemodels.rst:69
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The Network layer
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../../principles/network.rst:78
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`datagram`
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../../principles/reliability.rst:52
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:math:`10^6`
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../../principles/transport.rst:43 • ../../principles/transport.rst:49
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Bob : `What is the secret password ?`
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../../principles/sharing.rst:64
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In all these networks, except the full-mesh, the link bandwidth is shared among all connected hosts. Various algorithms have been proposed and are used to efficiently share the access to this resource. We explain several of them in the Medium Access Control section below.
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../../principles/security.rst:213
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When designing network protocols and applications that will be deployed on a large scale, it is important to take those DDoS attacks into account. Attackers use different strategies to launch DDoS attacks. Some have managed to gain control of a large number of sources by injecting malware on them. Others, and this is where protocol designers have an important role to play, simply exploit design flaws in some protocols. Consider a simple request-response protocol where the client sends a request and the server replies with a response. Often the response is larger or much larger than the request sent by the client. Consider that such a simple protocol is used over a datagram network. When Alice sends a datagram to Bob containing her request, Bob extracts both the request and Alice's address from the packet. He then sends his response in a single packet destined to Alice. Mallory would like to create a DoS attack against Alice without being identified. Since he has studied the specification of this protocol, he can send a request to Bob inside a packet having Alice's address as its source address. Bob will process the request and send his (large) response to Alice. If the response has the same size as the request, Mallory is producing a `reflection attack` since his packets are reflected by Bob. Alice would think that she is attacked by Bob. If there are many servers that operate the same service as Bob, Mallory could hide behind a large number of such reflectors. Unfortunately, the reflection attack can also become an amplification attack. This happens when the response sent by Bob is larger than the request that it has received. If the response is :math:`k` times larger than the request, then when Mallory consumes 1 Gbps of bandwidth to send requests, his victim receives :math:`k` Gbps of attack traffic. Such amplification attacks are a very important problem and protocol designers should ensure that they never send a large response before having received the proof that the request that they have received originated from the source indicated in the request.
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../../exercises/dns.rst:50
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Assume now that you are residing in a network where there is no DNS resolver and that you need to perform your query manually starting from the DNS root.
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../../exercises/http.rst:51
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The minimum command sent to a HTTP server is `GET / HTTP/1.0` followed by CRLF and a blank line.
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