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../../protocols/ipv6.rst:181
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``/64`` for a single user (e.g. a home user connected via ADSL)
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../../protocols/ethernet.rst:177
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1000Base-CX
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../../protocols/routing.rst:170
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See http://bgp.potaroo.net/index-as.html for reports on the evolution of the number of Autonomous Systems over time.
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../../protocols/tcp.rst:192
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When a TCP entity opens a TCP connection, it creates a Transmission Control Block (:term:`TCB`). The TCB contains the entire state that is maintained by the TCP entity for each TCP connection. During connection establishment, the TCB contains the local IP address, the remote IP address, the local port number, the remote port number, the current local sequence number and the last sequence number received from the remote entity. Until the mid 1990s, TCP implementations had a limit on the number of TCP connections that could be in the `SYN RCVD` state at a given time. Many implementations set this limit to about 100 TCBs. This limit was considered sufficient even for heavily load http servers given the small delay between the reception of a `SYN` segment and the reception of the `ACK` segment that terminates the establishment of the TCP connection. When the limit of 100 TCBs in the `SYN Rcvd` state is reached, the TCP entity discards all received TCP `SYN` segments that do not correspond to an existing TCB.
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../../protocols/tls.rst:294
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The server also sends a ``ChangeCipherSpec`` message followed by a ``Finished`` message.
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../../protocols/wifi.rst:157
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Footnotes
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../../bibliography.rst:335
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Stevens, R., `UNIX Network Programming, Volume 1, Second Edition: Networking APIs: Sockets and XTI <http://books.google.com/books?id=ptSC4LpwGA0C>`_, Prentice Hall, 1998
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../../glossary.rst:186
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HTTP
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../../principles/network.rst:251
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With the received `record route`, `B` can send a `data packet` to `A`. For this, it simply reverses the chosen `record route`. However, we still need to communicate the chosen path to `A`. This can be done by putting the `record route` inside a control packet which is sent back to `A` over the reverse path. An alternative is to simply send a `data packet` back to `A`. This packet will travel back to `A`. To allow `A` to inspect the entire path followed by the `data packet`, its `source route` must contain all intermediate routers when it is received by `A`. This can be achieved by encoding the `source route` using a data structure that contains an index and the ordered list of node addresses. The index always points to the next address in the `source route`. It is initialized at `0` when a packet is created and incremented by each intermediate node.
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../../principles/reliability.rst:222
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01111110000100100100100100100001101111110
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../../principles/transport.rst:167
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A second imperfection that may affect an `unreliable connectionless service` is that it may duplicate SDUs. Some packets may be duplicated in a network and be delivered twice to their destination. This is illustrated by the time-sequence diagram below.
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../../principles/sharing.rst:237
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In virtual circuit networks, another way to manage or prevent congestion is to limit the number of circuits that use the network at any time. This technique is usually called `connection admission control`. When a host requests the creation of a new circuit in the network, it specifies the destination and in some networking technologies the required bandwidth. With this information, the network can check whether there are enough resources available to reach this particular destination. If yes, the circuit is established. If not, the request is denied and the host will have to defer the creation of its virtual circuit. `Connection admission control` schemes are widely used in the telephone networks. In these networks, a busy tone corresponds to an unavailable destination or a congested network.
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../../principles/security.rst:593
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The two protocols above prevent eavesdropping attacks, but not man-in-the-middle attacks. If Mallory can intercept the messages sent by Alice, he could force her to reveal :math:`H^n(P)` and then use this information to authenticate as Alice on Bob's computer. In practice, hash chains should only be used when the communicating users know that there cannot be any man-in-the-middle on their communication.
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../../exercises/ipv6.rst:529
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With the previous exercises, you have learned how to reason about IPv6 networks "on paper". Given the availability of IPv6 implementations, it is also possible to carry out experiments in real and virtual labs. Several virtual environments are possible. In this section, we focus on mininet_. mininet_ is an emulation framework developed at Stanford University that leverages the namespaces features of recent Linux kernels. With those namespaces, a single Linux kernel can support a variety of routers and hosts interconnected by virtual links. mininet_ has been used by several universities as an educational tool, but unfortunately it was designed without IPv6 support.
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../../exercises/routing-protocols.rst:838
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It is interesting to look at the output of this command in details. Router `as1` has routes for three different IPv6 prefixes. The first prefix is its own prefix, ``2001:cafe:1::/48``. It has no nexthop since this prefix is originated by the router. Then, `as1` has received two paths for ``2001:cafe:2::/48``. In the BGP Loc-RIB, the `>` character indicates the best route according to the BGP decision process. ``2001:cafe:2::/48`` was learned over two different BGP sessions:
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../../exercises/tcp-2.rst:691
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Same question as above but now with a small variation. Recent TCP implementations use a large initial value for the congestion window. Draw the time-sequence diagram that corresponds to an initial value of 10000 bytes for this congestion window.
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../../protocols/bgp.rst:184
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In the above pseudo-code, the `build\_BGP\_update(d)` procedure extracts from the `BGP Loc-RIB` the best path towards destination `d` (i.e. the route installed in the FIB) and prepares the corresponding BGP `UPDATE` message. This message is then passed to the `export filter` that returns `None` if the route cannot be advertised to the peer or the (possibly modified) BGP `UPDATE` message to be advertised. BGP routers allow network administrators to specify very complex `export filters`, see e.g. [WMS2004]_. A simple `export filter` that implements the equivalent of `split horizon` is shown below.
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../../protocols/congestion.rst:240
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With the ECT bit, the deployment issue with ECN is solved provided that all sources cooperate. If some sources do not support ECN but still set the ECT bit in the packets that they sent, they will have an unfair advantage over the sources that correctly react to packet markings. Several solutions have been proposed to deal with this problem :rfc:`3540`, but they are outside the scope of this book.
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../../protocols/email.rst:232
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i
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../../protocols/ethernet.rst:211
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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.
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