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4. Zen

56 ../../protocols/ethernet.rst:211
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Increasing the physical layer bandwidth as in `Fast Ethernet` was only one of the solutions to improve the performance of Ethernet LANs. A second solution was to replace the hubs with more intelligent devices. As `Ethernet hubs` operate in the physical layer, they can only regenerate the electrical signal to extend the geographical reach of the network. From a performance perspective, it would be more interesting to have devices that operate in the datalink layer and can analyze the destination address of each frame and forward the frames selectively on the link that leads to the destination. Such devices are usually called `Ethernet switches` [#fbridges]_. An `Ethernet switch` is a relay that operates in the datalink layer as is illustrated in the figure below. 773/10000 · 773
56 ../../protocols/http.rst:189
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — All status codes starting with digit `4` indicate that the server has detected an error in the HTTP request sent by the client. `400 Bad Request` indicates a syntax error in the HTTP request. `404 Not Found` indicates that the requested document does not exist on the server. 275/10000 · 275
56 ../../protocols/ipv6.rst:182
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``/128`` in the rare case when it is known that no more than one host will be attached 86/10000 · 86
56 ../../protocols/ethernet.rst:177
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Two pairs shielded twisted pair, 25m maximum 44/10000 · 44
56 ../../protocols/routing.rst:173
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — OSPF can support `virtual links` to connect routers together that belong to the same area but are not directly connected. However, this goes beyond this introduction to OSPF. 174/10000 · 174
56 ../../protocols/tcp.rst:194
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — This limit of 100 TCBs in the `SYN Rcvd` state was chosen to protect the TCP entity from the risk of overloading its memory with too many TCBs in the `SYN Rcvd` state. However, it was also the reason for a new type of Denial of Service (DoS) attack :rfc:`4987`. A DoS attack is defined as an attack where an attacker can render a resource unavailable in the network. For example, an attacker may cause a DoS attack on a 2 Mbps link used by a company by sending more than 2 Mbps of packets through this link. In this case, the DoS attack was more subtle. As a TCP entity discards all received `SYN` segments as soon as it has 100 TCBs in the `SYN Rcvd` state, an attacker simply had to send a few 100 `SYN` segments every second to a server and never reply to the received `SYN+ACK` segments. To avoid being caught, attackers were of course sending these `SYN` segments with a different address than their own IP address [#fspoofing]_. On most TCP implementations, once a TCB entered the `SYN Rcvd` state, it remained in this state for several seconds, waiting for a retransmission of the initial `SYN` segment. This attack was later called a `SYN flood` attack and the servers of the ISP named panix were among the first to `be affected <http://memex.org/meme2-12.html>`_ by this attack. 1287/10000 · 1287
56 ../../protocols/tls.rst:297
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — TLS Cipher suites 17/10000 · 17
56 ../../protocols/wifi.rst:158
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The 802.11 working group defined the `basic service set (BSS)` as a group of devices that communicate with each other. We continue to use `network` when referring to a set of devices that communicate. 200/10000 · 200
56 ../../bibliography.rst:77
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Theodore Faber, Joe Touch, and Wei Yue, `The TIME-WAIT state in TCP and Its Effect on Busy Servers <https://dx.doi.org/10.1109/INFCOM.1999.752180>`_, Proceedings INFOCOM'99, pp. 1573 182/10000 · 182
57 ../../exercises/sockets.rst:390
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — For example, the ``htonl(3)`` (resp. ``ntohl(3)``) function the standard C library converts a 32-bits unsigned integer from the byte order used by the CPU to the network byte order (resp. from the network byte order to the CPU byte order). Similar functions exist in other programming languages. 295/10000 · 295
57 ../../bibliography.rst:78
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Feldmeier, D. C., `Fast software implementation of error detection codes <https://dx.doi.org/10.1109/90.477710>`_. IEEE/ACM Transactions Networking 3, 6 (Dec. 1995), 640-651. 174/10000 · 174
57 ../../exercises/network.rst:374
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — C 1/10000 · 1
57 ../../glossary.rst:179
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A relay operating in the physical layer. 40/10000 · 40
57 ../../principles/network.rst:345
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The last, but important, point to discuss about the `data plane` of the networks that rely on the datagram mode is their addressing scheme. In the examples above, we have used letters to represent the addresses of the hosts and network nodes. In practice, all addresses are encoded as a bit string. Most network technologies use a fixed size bit string to represent source and destination address. These addresses can be organized in two different ways. 453/10000 · 453
57 ../../principles/reliability.rst:232
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 01111110011011111011111011111011001001111110 44/10000 · 44
57 ../../principles/sharing.rst:374
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The common problem among Local Area Networks is how to efficiently share the available bandwidth. If two devices send a frame at the same time, the two electrical, optical or radio signals that correspond to these frames will appear at the same time on the transmission medium and a receiver will not be able to decode either frame. Such simultaneous transmissions are called `collisions`. A `collision` may involve frames transmitted by two or more devices attached to the Local Area Network. Collisions are the main cause of errors in wired Local Area Networks. 563/10000 · 563
57 ../../principles/transport.rst:234
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — As the transport layer is built on top of the network layer, it is important to know the key features of the network layer service. In this book, we only consider the `connectionless network layer service` which is the most widespread. Its main characteristics are : 266/10000 · 266
57 ../../principles/security.rst:600
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Public key cryptography provides another possibility to allow Alice to authenticate herself on Bob's computer. Assume again that Alice and Bob know each other from previous encounters. Alice knows Bob's public key (:math:`Bob_{pub}`) and Bob also knows Alice's key (:math:`Alice_{pub}`). To authenticate herself, Alice could send her user identifier. Bob would reply with a random number encrypted with Alice's public key : :math:`E_p(Alice_{pub},R)`. Alice can decrypt this message to recover `R` and sends :math:`E_p(Bob_{pub},R)`. Bob decrypts the nonce and confirms that Alice knows :math:`Alice_{priv}`. If an eavesdropper captures the messages exchanged, he cannot recover the value `R` which could be used as a key to encrypt the information with a secret key algorithm. This is illustrated in the time sequence diagram below. 833/10000 · 833
57 ../../exercises/ipv6.rst:531
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — During the last years, `Olivier Tilmans <https://inl.info.ucl.ac.be/otilmans.html>`_ and `Mathieu Jadin <https://inl.info.ucl.ac.be/mjadin.html>`_ have developed the missing piece to enable students to use mininet_ to experiment with IPv6: ipmininet_. ipmininet_ is a python module that provides the classes that are required to automatically configure IPv6 networks with different routing protocols. It is available from PyPi from https://pypi.python.org/ipmininet. 467/10000 · 467
57 ../../exercises/routing-protocols.rst:840
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — the eBGP session with ``fe80::3c81:2eff:fe19:465d`` with an AS-Path of ``AS3:AS2`` (see last column) 100/10000 · 100