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../../protocols/ipv6.rst:77
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IP version 6
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../../protocols/ppp.rst:21
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The PPP framing :rfc:`1662` was inspired by the datalink layer protocols standardized by ITU-T and ISO. A typical PPP frame is composed of the fields shown in the figure below. A PPP frame starts with a one byte flag containing `01111110`. PPP can use bit stuffing or character stuffing depending on the environment where the protocol is used. The address and control fields are present for backward compatibility reasons. The 16 bit Protocol field contains the identifier [#fpppid]_ of the network layer protocol that is carried in the PPP frame. `0x002d` is used for an IPv4 packet compressed with :rfc:`1144` while `0x002f` is used for an uncompressed IPv4 packet. `0xc021` is used by the Link Control Protocol, `0xc023` is used by the Password Authentication Protocol (PAP). `0x0057` is used for IPv6 packets. PPP supports variable length packets, but LCP can negotiate a maximum packet length. The PPP frame ends with a Frame Check Sequence. The default is a 16 bits CRC, but some implementations can negotiate a 32 bits CRC. The frame ends with the `01111110` flag.
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../../protocols/ppp.rst:31
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PPP played a key role in allowing Internet Service Providers to provide dial-up access over modems in the late 1990s and early 2000s. ISPs operated modem banks connected to the telephone network. For these ISPs, a key issue was to authenticate each user connected through the telephone network. This authentication was performed by using the `Extensible Authentication Protocol` (EAP) defined in :rfc:`3748`. EAP is a simple, but extensible protocol that was initially used by access routers to authenticate the users connected through dial-up lines. Several authentication methods, starting from the simple username/password pairs to more complex schemes have been defined and implemented. When ISPs started to upgrade their physical infrastructure to provide Internet access over `Asymmetric Digital Subscriber Lines` (ADSL), they tried to reuse their existing authentication (and billing) systems. To meet these requirements, the IETF developed specifications to allow PPP frames to be transported over other networks than the point-to-point links for which PPP was designed. Nowadays, most ADSL deployments use PPP over either ATM :rfc:`2364` or Ethernet :rfc:`2516`.
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../../protocols/routing.rst:31
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In this section, we briefly describe the key features of the two main intradomain unicast routing protocols : RIP and OSPF. The basic principles of distance vector and link-state routing have been presented earlier.
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../../protocols/rpc.rst:20
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The first problem to be solved is how to transfer the information from the caller to the callee. This problem is not simple and includes two sub-problems. The first sub-problem is the encoding of the information. How to encode the values of the parameters so that they can be transferred correctly through the network ? The second problem is how to reach the callee through the network ? The callee is identified by a procedure name, but to use the transport service, we need to convert this name into an address and a port number.
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../../protocols/ssh.rst:85
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encryption
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../../protocols/tcp.rst:26
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To provide this service, TCP relies on a simple segment format that is shown in the figure below. Each TCP segment contains a header described below and, optionally, a payload. The default length of the TCP header is twenty bytes, but some TCP headers contain options.
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../../protocols/tls.rst:43
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../../protocols/transport-service.rst:22
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`IP version 4` addresses that are 32 bits wide
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../../protocols/udp.rst:51
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The UDP header contains four fields :
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../../protocols/wifi.rst:19
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Range (m) indoor/outdoor
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../../bibliography.rst:36
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Buford, J., Yu, H., Lua, E.K., `P2P Networking and Applications <http://books.google.com/books?id=O9NkAaY9YxMC>`_, Morgan Kaufmann, 2008
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../../glossary.rst:270
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The Address Resolution Protocol is a protocol used by IPv4 devices to obtain the datalink layer address that corresponds to an IPv4 address on the local area network. ARP is defined in :rfc:`826`
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../../exercises/ex-sharing.rst:203
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In practice, hosts transmit variable length frames. Consider a cable having a bandwidth of 100 Mbps and a length of 2 kilometers.
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../../principles/sharing.rst:45
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A fourth physical organization of a network is the ring topology. Like the bus organization, each host has a single physical interface connecting it to the ring. Any signal sent by a host on the ring will be received by all hosts attached to the ring. From a redundancy point of view, a single ring is not the best solution, as the signal only travels in one direction on the ring; thus if one of the links composing the ring is cut, the entire network fails. In practice, such rings have been used in local area networks, but are now often replaced by star-shaped networks. In metropolitan networks, rings are often used to interconnect multiple locations. In this case, two parallel links, composed of different cables, are often used for redundancy. With such a dual ring, when one ring fails all the traffic can be quickly switched to the other ring.
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../../principles/security.rst:134
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In the previous example, we have explained how Eve could capture data from a particular user. This is not the only attack of this type. In 2013, based on documents collected by Edward Snowden, the press revealed that several governmental agencies were collecting lots of data on various links that compose the global Internet [Greenwald2014]_. Thanks to this massive amount of data, these governmental agencies have been able to extract lots of information about the behavior of Internet users. Like Eve, they are in a position to extract passwords, usernames and other privacy sensitive data from all the packets that they have captured. However, it seems that these agencies were often more interested in various meta data, e.g. information showing with whom a given user communicates than the actual data exchanged. These revelations have shocked the Internet community and the `Internet Engineering Task Force <https://www.ietf.org>`_ that manages the standardization of Internet protocols has declared in :rfc:`7258` that such pervasive monitoring is an attack that need to be countered in the development of new protocols. Several new protocols and extensions to existing ones are being developed to counter these attacks.
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../../exercises/dns.rst:39
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dig_ also contains some additional parameters and flags that are described in the man page. Among these, the `+trace` flag allows to trace all requests that are sent when recursively contacting DNS servers.
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../../exercises/http.rst:31
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The `ipvfoo <https://code.google.com/p/ipvfoo/>`_ extension on google chrome allows the user to visually detect whether a website is using IPv6 and IPv4, but also to see which web sites have been contacted when rendering a given web page. Some websites are distributed over several dozens of different servers. Can you find one ?
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../../exercises/ipv6.rst:40 • ../../exercises/ipv6.rst:149
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router ``R1`` uses address ``2001:db8:1341:1::1`` on its West interface, address ``2001:db8:1341:12::1`` on its East interface and address ``2001:db8:1341:13::1`` on its South interface
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../../exercises/lan.rst:77
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In the network represented in Fig. 4, can the host `H0` communicate with `H1` and vice-versa? Explain. Add whatever you need in the network to allow them to communicate.
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