Exit Zen
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../../exercises/sockets.rst:173
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Depending on the socket address family, the operating system might implicitly assign an address to an unbound socket upon a call to ``write``, ``send`` or ``sendto``. While this is a useful behavior, describing it precisely is out of the scope of this section.
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../../exercises/transport.rst:141
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DATA segments contain a sequence number that is incremented for each byte transmitted
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../../principles/naming.rst:110
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the nameserver(s) that are responsible for any direct sub-domain of domain `dom` (i.e. `sdom1.dom` and `sdom2.dom` in the figure above, but not `z.sdom1.dom`)
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../../principles/referencemodels.rst:85
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The Transport layer
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../../principles/network.rst:85
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The first and most popular organization of the network layer is the datagram organization. This organization is inspired by the organization of the postal service. Each host is identified by a `network layer address`. To send information to a remote host, a host creates a packet that contains:
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../../principles/reliability.rst:54
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1 Tbps
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../../principles/transport.rst:47
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If Alice wants to enter the meeting room but does not know the password, her conversation could be as follows :
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../../principles/sharing.rst:101
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In large networks, fairness is always a compromise. The most widely used definition of fairness is the `max-min fairness`. A bandwidth allocation in a network is said to be `max-min fair` if it is such that it is impossible to allocate more bandwidth to one of the flows without reducing the bandwidth of a flow that already has a smaller allocation than the flow that we want to increase. If the network is completely known, it is possible to derive a `max-min fair` allocation as follows. Initially, all flows have a null bandwidth and they are placed in the candidate set. The bandwidth allocation of all flows in the candidate set is increased until one link becomes congested. At this point, the flows that use the congested link have reached their maximum allocation. They are removed from the candidate set and the process continues until the candidate set becomes empty.
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../../protocols/dns.rst:65
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`CNAME` (or canonical names) are used to define aliases. For example `www.example.com` could be a `CNAME` for `pc12.example.com` that is the actual name of the server on which the web server for `www.example.com` runs.
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../../principles/security.rst:261
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The security of the Caesar cipher depends on the confidentiality of the algorithm, but experience has shown that it is impossible to assume that an algorithm will remain secret, even for military applications. Instead, cryptographic techniques must be designed by assuming that the algorithm will be public and known to anyone. However, its behavior must be controlled by a small parameter, known as the key, that will only be known by the users who need to communicate secretly. This principle is attributed to Auguste Kerckhoff, a French cryptographer who first documented it :
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../../exercises/dns.rst:54
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Continue until you find the server responsible for `www.root-servers.org`
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../../exercises/http.rst:57
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There are probably very few websites that only support IPv6 and not IPv4. If you find one, let us know by submitting a pull-request to change this exercise.
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../../exercises/ipv6.rst:150 • ../../exercises/ipv6.rst:228
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router ``R2`` uses address ``2001:db8:1341:12::2`` on its West interface, and address ``2001:db8:1341:24::2`` on its South interface
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../../exercises/lan.rst:193
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The ``addSwitch`` method creates an Ethernet switch. It assigns a random MAC address to each switch and we can configure it with a priority that is used in the high order bits of the switch identifier. We add one IP address to each switch so that we can connect to them on mininet_. In practice, IPMininet_ configures the :manpage:`brtcl(8)` software that implements the Spanning Tree protocol on Linux. We can then create the links, configure their cost if required and launch tcpdump_ to capture the Ethernet frames that contain the messages of the Spanning Tree protocol.
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../../exercises/routing-policies.rst:165
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On recent routers, a lookup in the forwarding table for a destination address returns a set of outgoing interfaces. How would you design an algorithm that selects the outgoing interface used for each packet, knowing that to avoid reordering, all segments of a given TCP connection should follow the same path ?
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../../exercises/routing-protocols.rst:257
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Router ``r2`` reacts to this updated Database description packet by requesting the link state information that it does not already know. For this, it sends a `LS Request` packet.
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../../exercises/tcp-2.rst:105
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The :manpage:`accept` system call returns a new file descriptor, in this case value ``4``. At this point, packetdrill_ can write data on the socket or inject packets.
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../../exercises/trace.rst:107
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Use wireshark to analyze the packet traces described earlier :download:`traces/simple-trace.pcap`.
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../../protocols/bgp.rst:66
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The second type of peering relationship is the `shared-cost` peering relationship. Such a relationship usually does not involve a payment from one domain to the other in contrast with the `customer->provider` relationship. A `shared-cost` peering relationship is usually established between domains having a similar size and geographic coverage. For example, consider the figure above. If `AS3` and `AS4` exchange many packets via `AS1`, they both need to pay `AS1`. A cheaper alternative for `AS3` and `AS4` would be to establish a `shared-cost` peering. Such a peering can be established at IXPs where both `AS3` and `AS4` are present or by using private peering links. This `shared-cost` peering should be used to exchange packets between hosts inside `AS3` and hosts inside `AS4`. However, `AS3` does not want to receive on the `AS3-AS4` `shared-cost` peering links packets whose destination belongs to `AS1` as `AS3` would have to pay to send these packets to `AS1`.
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../../protocols/congestion.rst:106
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As explained earlier, Explicit Congestion Notification :rfc:`3168` improves the detection of congestion by allowing routers to explicitly mark packets when they are lightly congested. In theory, a single bit in the packet header [RJ1995]_ is sufficient to support this congestion control scheme. When a host receives a marked packet, it returns the congestion information to the source that adapts its transmission rate accordingly. Although the idea is relatively simple, deploying it on the entire Internet has proven to be challenging [KNT2013]_. It is interesting to analyze the different factors that have hindered the deployment of this technique.
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