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19 ../../principles/sharing.rst:182
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Besides the link bandwidth, the buffers on the network nodes are the second type of resource that needs to be shared inside the network. The node buffers play an important role in the operation of the network because that can be used to absorb transient traffic peaks. Consider again the example above. Assume that on average host `A` and host `B` send a group of three packets every ten seconds. Their combined transmission rate (0.6 packets per second) is, on average, lower than the network capacity (1 packet per second). However, if they both start to transmit at the same time, node `R1` will have to absorb a burst of packets. This burst of packets is a small `network congestion`. We will say that a network is congested, when the sum of the traffic demand from the hosts is larger than the network capacity :math:`\sum{demand}>capacity`. This `network congestion` problem is one of the most difficult resource sharing problem in computer networks. `Congestion` occurs in almost all networks. Minimizing the amount of congestion is a key objective for many network operators. In most cases, they will have to accept transient congestion, i.e. congestion lasting a few seconds or perhaps minutes, but will want to prevent congestion that lasts days or months. For this, they can rely on a wide range of solutions. We briefly present some of these in the paragraphs below. 1378/10000 · 1378
19 ../../principles/transport.rst:65
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Alice : `3.1415` 16/10000 · 16
19 ../../protocols/dns.rst:64
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — `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. 218/10000 · 218
19 ../../principles/security.rst:261
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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 : 579/10000 · 579
19 ../../exercises/dns.rst:54
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Continue until you find the server responsible for `www.root-servers.org` 73/10000 · 73
19 ../../exercises/http.rst:57
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 156/10000 · 156
19 ../../exercises/ipv6.rst:150 • ../../exercises/ipv6.rst:228
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — router ``R2`` uses address ``2001:db8:1341:12::2`` on its West interface, and address ``2001:db8:1341:24::2`` on its South interface 132/10000 · 132
19 ../../exercises/lan.rst:193
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 574/10000 · 574
19 ../../exercises/routing-policies.rst:165
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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 ? 310/10000 · 310
19 ../../exercises/routing-protocols.rst:257
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 178/10000 · 178
19 ../../exercises/tcp-2.rst:105
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 166/10000 · 166
19 ../../exercises/trace.rst:107
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Use wireshark to analyze the packet traces described earlier :download:`traces/simple-trace.pcap`. 98/10000 · 98
19 ../../protocols/bgp.rst:66
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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`. 971/10000 · 971
19 ../../protocols/congestion.rst:106
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 653/10000 · 653
19 ../../protocols/dnssec.rst:182
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The security of DNSSEC relies on `anchored keys`. An `anchored key` is a public key that is considered as trusted by a resolver. In our example, we assume that Alice's resolver has obtained the public key of the servers that manage the root zone in a secure way. This key has been distributed outside of the DNS, e.g. it has been published in a newspaper or has been received in a sealed letter. 395/10000 · 395
19 ../../protocols/email.rst:106
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — the `cc:` header line is used by the sender to provide a list of email addresses that must receive a carbon copy of the message. Several addresses can be listed in this header line, separated by commas. All recipients of the email message receive the `To:` and `cc:` header lines. 280/10000 · 280
19 ../../protocols/ethernet.rst:109
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Several physical layers have been defined for Ethernet networks. The first physical layer, usually called 10Base5, provided 10 Mbps over a thick coaxial cable. The characteristics of the cable and the transceivers that were used then enabled the utilization of 500 meter long segments. A 10Base5 network can also include repeaters between segments. 348/10000 · 348
19 ../../protocols/http.rst:94
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The second component of the `word wide web` is the HyperText Markup Language (HTML). HTML defines the format of the documents that are exchanged on the `web`. The `first version of HTML <http://www.w3.org/History/19921103-hypertext/hypertext/WWW/MarkUp/Tags.html>`_ was derived from the Standard Generalized Markup Language (SGML) that was standardized in 1986 by :term:`ISO`. SGML_ was designed to support large documents maintained by government, law firms or aerospace companies that must be shared efficiently in a machine-readable manner. These industries require documents to remain readable and editable for tens of years and insisted on a standardized format supported by multiple vendors. Today, SGML_ is no longer widely used beyond specific applications, but its descendants including :term:`HTML` and :term:`XML` are now widespread. 844/10000 · 844
19 ../../protocols/http2.rst:141
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Another limitation of HTTP/1.1 is that all commands and parameters are encoded as ASCII strings. Using ASCII strings makes it easy to write simple clients or debug problems by observing packets. Unfortunately, the burden is placed on servers that need to include complex parsers that accept a wide range of partially compliant implementations. Furthermore, the flexibility of the ASCII encoding has enabled some classes of security attacks on servers [CWE444]_. 461/10000 · 461
19 ../../protocols/ipv6.rst:97
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A host should be able to configure its IPv6 address automatically 65/10000 · 65