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../../protocols/dnssec.rst:86
English
Fortunately, designers of DNS servers and resolvers have found solutions to mitigate this type of attack. The easiest approach would have been to update the format of the DNS requests and responses to include a larger `Identifier` field. Unfortunately, this elegant solution was not possible with the DNS because the DNS messages do not include any version number that would have enabled such a change. Since the DNS messages are exchanged inside UDP segments, the DNS developers found an alternate solution to counter this attack. There are two ways for the DNS library used by Alice to send her DNS requests. A first solution is to bind one UDP source port and always send the DNS requests from this source port (the destination port is always port ``53``). The advantage of this solution is that Alice's DNS library can easily receive the DNS responses by listening to her chosen port. Unfortunately, once the attacker has found the source port used by Alice, he only needs to send 65,536 DNS responses to inject an invalid response. Fortunately, Alice can send her DNS requests in a different way. Instead of using the same source port for all DNS requests, she can use a different source port for each request. In practice, each DNS request will be sent from a different source port. From an implementation viewpoint, this implies that Alice's DNS library will need to listen to one different port number for each pending DNS request. This increases the complexity of her implementation. From a security viewpoint there is a clear benefit since the attacker needs to guess both the 16 bits `Identifier` and the 16 bits `UDP source port` to inject a fake DNS response. To generate all possible DNS responses, the attacker would need to generate almost :math:`2^{32}` different messages, which is excessive in today's networks. Most DNS implementations use this second approach to prevent these cache poisoning attacks.
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../../protocols/email.rst:54
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We will first discuss the format of email messages followed by the protocols that are used on today's Internet to exchange and retrieve emails. Other email systems have been developed in the past [Bush1993]_ [Genilloud1990]_ [GC2000]_, but today most email solutions have migrated to the Internet email. Information about the software that is used to compose and deliver emails may be found on wikipedia_ among others, for both `email clients`_ and `email servers <http://en.wikipedia.org/wiki/Comparison_of_mail_servers>`_. More detailed information about the full Internet Mail Architecture may be found in :rfc:`5598`.
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../../protocols/ethernet.rst:68
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Ethernet DIX frame format
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../../protocols/http.rst:48
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A standardized addressing scheme that unambiguously identifies documents
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../../protocols/http2.rst:57
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A first approach is to store all files on each physical server and rely on the DNS to distribute the load among them. Each physical server has its own IP address and when the DNS server receives a query for `www.service.net`, it returns the IP address of one of them. Some DNS servers use Round-Robin to return one of these IP addresses. Others measure the load of the physical servers and return the address of the less loaded one. Another possibility is to locate the physical servers in different regions and configure the DNS server to return the IP address of the server that is geographically closer to the client's IP address.
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../../protocols/ipv6.rst:73
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Unfortunately no datalink layer is able to send frames of unlimited side. Each datalink layer is characterized by a maximum frame size. There are more than a dozen different datalink layers and unfortunately most of them use a different maximum frame size. The network layer must cope with the heterogeneity of the datalink layer.
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../../protocols/ppp.rst:19
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The `Network Control Protocol` that is specific for each network layer protocol. It is used to negotiate options that are specific for each protocol. For example, IPv4's NCP :rfc:`1548` can negotiate the IPv4 address to be used, the IPv4 address of the DNS resolver. IPv6's NCP is defined in :rfc:`5072`.
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../../protocols/ppp.rst:27
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PPP frame format
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../../protocols/routing.rst:29
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Intradomain routing
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../../protocols/rpc.rst:18
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This model was developed with a single host in mind. How should it be modified if the caller and the callee are different hosts connected through a network ? Since the two hosts can be different, the two main problems are the fact they do not share the same memory and that they do not necessarily use the same representation for numbers, characters, ... Let us examine how the five steps identified above can be supported through a network.
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../../protocols/ssh.rst:84
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key exchange
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../../protocols/tcp.rst:22
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On the global Internet, most of the applications used in the wide area rely on TCP. Many studies [#ftcpusage]_ have reported that TCP was responsible for more than 90% of the data exchanged in the global Internet.
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../../protocols/tls.rst:43
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POP3
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../../protocols/transport-service.rst:20
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On the Internet, the `port number` is an integer and the `host` is identified by its network address. There are two types of Internet addresses :
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../../protocols/udp.rst:49
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UDP Header Format
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../../protocols/wifi.rst:19
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Max bandwidth
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../../bibliography.rst:35
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Bux, W., `Token-ring local-area networks and their performance <http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=18625>`_, Proceedings of the IEEE, Vol 77, No 2, p. 238-259, Feb. 1989
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../../glossary.rst:268
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ARP
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../../exercises/ex-sharing.rst:175
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Same question as above, but now assume that the retransmission timer of each host is set to 50 microseconds.
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../../principles/security.rst:132
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Pervasive monitoring
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