Exit Zen
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../../protocols/ethernet.rst:179 • ../../protocols/ethernet.rst:358
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10 Gbps
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../../protocols/http.rst:166
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the `Last-Modified:` header indicates the date and time of the last modification of the document attached to the HTTP response.
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../../protocols/ipv6.rst:159
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The subnet identifier plays a key role in the scalability of network layer addressing architecture. An important point to be defined in a network layer protocol is the allocation of the network layer addresses. A naive allocation scheme would be to provide an address to each host when the host is attached to the Internet on a first come first served basis. With this solution, a host in Belgium could have address ``2001:db8::1`` while another host located in Africa would use address ``2001:db8::2``. Unfortunately, this would force all routers on the Internet to maintain one route towards each host. In the network layer, scalability is often a function of the number of routes stored on the router. A network will usually work better if its routers store fewer routes and network administrators usually try to minimize the number of routes that are known by their routers. For this, they often divide their network prefix in smaller blocks. For example, consider a company with three campuses, a large one and two smaller ones. The network administrator would probably divide his block of addresses as follows :
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../../protocols/ethernet.rst:171
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Thick coaxial cable, 500m
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../../protocols/routing.rst:143
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the routers that are adjacent to the failure detect it quickly. The default solution is to rely on the regular exchange of HELLO packets. However, the interval between successive HELLOs is often set to 10 seconds... Setting the HELLO timer down to a few milliseconds is difficult as HELLO packets are created and processed by the main CPU of the routers and these routers cannot easily generate and process a HELLO packet every millisecond on each of their interfaces. A better solution is to use a dedicated failure detection protocol such as the Bidirectional Forwarding Detection (BFD) protocol defined in [KW2009]_ that can be implemented directly on the router interfaces. Another solution to be able to detect the failure is to instrument the physical and the datalink layer so that they can interrupt the router when a link fails. Unfortunately, such a solution cannot be used on all types of physical and datalink layers.
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../../protocols/tcp.rst:137
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In the figure above, the connection is considered to be established by the client once it has received the `SYN+ACK` segment, while the server considers the connection to be established upon reception of the `ACK` segment. The first data segment sent by the client (server) has its `sequence number` set to `x+1` (resp. `y+1`).
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../../protocols/tls.rst:200
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the ``Certificate`` message provides the certificate (or usually a chain of certificates) that binds a domain name to the public key used by the server. TLS uses the server certificates to authenticate the server. It relies on a Public Key Infrastructure that is composed of a set of root certification authorities that issue certificates to certification authorities that in the end issue certificates to servers. TLS clients are usually configured with the public keys of several root certification authorities and use this information to validate the certificates that they receive from servers. For historical reasons, the TLS certificates are encoded in ASN.1 format. The details of the ASN.1 syntax [Dubuisson2000]_ are outside the scope of this book.
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../../protocols/wifi.rst:115
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IEEE 802.11 ACK and CTS frames
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../../bibliography.rst:308
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Ramakrishnan, K. K. and Jain, R., `A binary feedback scheme for congestion avoidance in computer networks with a connectionless network layer <http://doi.acm.org/10.1145/205447.205461>`_. SIGCOMM Computer Communication Review 25, 1 (Jan. 1995), 138-156.
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../../glossary.rst:65
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a frame is the unit of information transfer in the datalink layer
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../../exercises/network.rst:363 • ../../exercises/network.rst:364 • ../../exercises/network.rst:365 • ../../exercises/network.rst:366 • ../../exercises/network.rst:367
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../../exercises/sockets.rst:335
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Besides 16 and 32 bit words, some applications need to exchange data structures containing bit fields of various lengths. For example, a message may be composed of a 16 bits field followed by eight, one bit flags, a 24 bits field and two 8 bits bytes. Internet protocol specifications will define such a message by using a representation such as the one below. In this representation, each line corresponds to 32 bits and the vertical lines are used to delineate fields. The numbers above the lines indicate the bit positions in the 32-bits word, with the high order bit at position `0`.
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../../principles/reliability.rst:199
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If the physical layer were perfect, the problem would be very simple. We would simply need to define how to encode each frame as a sequence of consecutive bits. The receiver would then easily be able to extract the frames from the received bits. Unfortunately, the imperfections of the physical layer make this framing problem slightly more complex. Several solutions have been proposed and are used in practice in different network technologies.
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../../principles/transport.rst:99
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Message format
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../../principles/security.rst:450
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SHA-1 is a cryptographic hash function that was standardized by the NIST in 1995. It outputs 160 bits results. It is now used in a variety of network protocols.
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../../exercises/ipv6.rst:474
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``p:0001::/64`` used on the link ``A2-R3``. ``A2`` uses address ``p:0001::A2/64``
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../../exercises/routing-protocols.rst:540
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We can also use :manpage:`traceroute6(8)` to check the path followed by the packets. Before doing that, think about the configuration of the BGP routing policies and try to predict the output of :manpage:`traceroute6(8)`. This is a good exercise to check your understanding of BGP.
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../../exercises/tcp-2.rst:641
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the sender/receiver performs a single :manpage:`send(3)` of `x` bytes
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../../protocols/bgp.rst:135
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In the remainder of this chapter, and although all routing information is exchanged using BGP `UPDATE` messages, we assume for simplicity that a BGP message contains only information about one prefix and we use the words :
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../../protocols/congestion.rst:216
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:math:`Throughput<\min(\frac{window}{rtt},\frac{k \times MSS}{rtt \times \sqrt{p}})`
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