Exit Zen
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../../protocols/ipv6.rst:180
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``/56`` for small user sites
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../../protocols/ethernet.rst:176
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Two multi-mode optical fiber, 2 km maximum
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../../protocols/routing.rst:169
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Footnotes
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../../protocols/tcp.rst:None
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Denial of Service attacks
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../../protocols/tls.rst:283
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The client sends the ``ChangeCipherSpec`` message followed by the ``Finished`` message. The ``ChangeCipherSpec`` message indicates that the client has received all the information required to generate the security keys for this TLS session. This messages can also appear later in the session to indicate a change in the encryption algorithms that are used, but this usage is outside the scope of this book. The ``Finished`` message is more important. It confirms to the server that the TLS handshake has been performed correctly and that no attacker has been able to modify the data sent by the client or the server. This is the first message that is encrypted with the selected security keys. It contains a hash of all the messages that were exchanged during the handshake.
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../../protocols/wifi.rst:154
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The second important utilization of the management frames is to allow a WiFi station to be associated with an access point. When a WiFi station starts, it listens to beacon frames to find the available SSIDs. To be allowed to send and receive frames via an access point, a WiFi station must be associated to this access point. If the access point does not use any security mechanism to secure the wireless transmission, the WiFi station simply sends an `Association request` frame to its preferred access point (usually the access point that it receives with the strongest radio signal). This frame contains some parameters chosen by the WiFi station and the SSID that it requests to join. The access point replies with an `Association response frame` if it accepts the WiFI station.
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../../bibliography.rst:330
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Sklower, K. 1989. `Improving the efficiency of the OSI checksum calculation <http://doi.acm.org/10.1145/74681.74684>`_. SIGCOMM Computer Communication Review 19, 5 (Oct. 1989), 32-43.
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../../glossary.rst:264
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The HyperText Markup Language specifies the structure and the syntax of the documents that are exchanged on the world wide web. HTML is maintained by the `HTML working group <https://www.w3.org/html/wg/>`_ of the :term:`W3C`
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../../principles/network.rst:249
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For example, consider again the network topology above. `A` sends a control packet towards `B`. The initial `record route` is empty. When `R1` receives the packet, it adds its own address to the `record route` and forwards a copy to `R2` and another to `R3`. `R2` receives the packet, adds itself to the `record route` and forwards it to `R3`. `R3` receives two copies of the packet. The first contains the `[R1,R2]` `record route` and the second `[R1]`. In the end, `B` will receive two control packets containing `[R1,R2,R3,R4]` and `[R1,R3,R4]` as `record routes`. `B` can keep these two paths or select the best one and discard the second. A popular heuristic is to select the `record route` of the first received packet as being the best one since this likely corresponds to the shortest delay path.
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../../principles/reliability.rst:222
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0001001001001001001000011
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../../principles/transport.rst:165
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In practice, an `unreliable connectionless service` will usually deliver a large fraction of the SDUs. However, since the delivery of SDUs is not guaranteed, the user must be able to recover from the loss of any SDU.
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../../principles/security.rst:571
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A better approach would be to authenticate Alice without storing her password in clear on Bob's computer. For this, Alice computes a `hash chain` as proposed by Lamport in [Lamport1981]_. A hash chain is a sequence of applications of a hash function (`H`) on an input string. If Alice's password is `P`, then her 10 steps hash chain is : :math:`H(H(H(H(H(H(H(H(H(H(P))))))))))`. The result of this hash chain will be stored on Bob's computer together with the value `10`. This number is the maximum number of remaining authentications for Alice on Bob's computer. To authenticate Alice, Bob sends the remaining number of authentications, i.e. `10` in this example. Since Alice knows her password, `P`, she can compute :math:`H^9(P)=H(H(H(H(H(H(H(H(H(P)))))))))` and send this information to Bob. Bob computes the hash of the value received from Alice (:math:`H(H^9(P))`) and verifies that this value is equal to the value stored in his database. It then decrements the number of authorized authentications and stores :math:`H^9(P)` in his database. Bob is now ready for the next authentication of Alice. When the number of authorized authentications reaches zero, the hash chain needs to be reinitialized. If Eve captures :math:`(H^n(P))`, she cannot use it to authenticate herself as Alice on Bob's computer because Bob will have decremented its number of authorized authentications. Furthermore, given that hash functions are not invertible, Eve cannot compute :math:`H^{n-1}(P)` from :math:`H^{n}(P)`.
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../../exercises/ipv6.rst:527
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Configuring IPv6 Networks
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../../exercises/routing-protocols.rst:812
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We can now observe the BGP-Loc-RIB of the router with the ``show bgp ipv6 command`` command.
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../../exercises/tcp-2.rst:688
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How long does it take for the sender to deliver 3 KBytes to the receiver ?
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../../protocols/bgp.rst:166
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When a BGP session starts, the routers first exchange `OPEN` messages to negotiate the options that apply throughout the entire session. Then, each router extracts from its FIB the routes to be advertised to the peer. It is important to note that, for each known destination prefix, a BGP router can only advertise to a peer the route that it has itself installed inside its `FIB`. The routes that are advertised to a peer must pass the peer's `export filter`. The `export filter` is a set of rules that define which routes can be advertised over the corresponding session, possibly after having modified some of its attributes. One `export filter` is associated to each BGP session. For example, on a `shared-cost peering`, the `export filter` only selects the internal routes and the routes that have been learned from a `customer`. The pseudo-code below shows the initialization of a BGP session.
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../../protocols/congestion.rst:238
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In enterprise networks or datacenters, the situation is different since a single company typically controls all the sources and all the routers. In such networks it is possible to ensure that all hosts and routers have been upgraded before turning on ECN on the routers.
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../../protocols/email.rst:232
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../../protocols/ethernet.rst:207
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Ethernet Switches
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../../protocols/http.rst:188
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All status codes starting with digit `3` indicate that the requested document is no longer available on the server. `301 Moved Permanently` indicates that the requested document is no longer available on this server. A `Location:` header containing the new URI of the requested document is inserted in the HTTP response. `304 Not Modified` is used in response to an HTTP request containing the `If-Modified-Since:` header. This status line is used by the server if the document stored on the server is not more recent than the date indicated in the `If-Modified-Since:` header.
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