2. cnp3-ebook
3. English
4. Zen

14 ../../principles/naming.rst:79
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The Domain Name System was created at a time when the Internet was mainly used in North America. The initial design assumed that all domain names would be composed of letters and digits :rfc:`1035`. As Internet usage grew in other parts of the world, it became important to support non-ASCII characters. For this, extensions have been proposed to the Domain Name System :rfc:`3490`. In a nutshell, the solution that is used to support Internationalized Domain Names works as follows. First, it is possible to use most of the Unicode characters to encode domain names and hostnames, with a few exceptions (for example, the dot character cannot be part of a name since it is used as a separator). Once a domain name has been encoded as a series of Unicode characters, it is then converted into a string that contains the ``xn--`` prefix and a sequence of ASCII characters. More details on these algorithms can be found in :rfc:`3490` and :rfc:`3492`. 948/10000 · 948
14 ../../principles/network.rst:90
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — There are two possible organizations for the network layer : 60/10000 · 60
14 ../../principles/referencemodels.rst:76
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — An important point to note about the `Datalink layer` is that although the figure below indicates that two entities of the `Datalink layer` exchange frames directly, in reality this is slightly different. When the `Datalink layer` entity on the left needs to transmit a frame, it issues as many `Data.request` primitives to the underlying `physical layer` as there are bits in the frame. The physical layer will then convert the sequence of bits in an electromagnetic or optical signal that will be sent over the physical medium. The `physical layer` on the right hand side of the figure will decode the received signal, recover the bits and issue the corresponding `Data.indication` primitives to its `Datalink layer` entity. If there are no transmission errors, this entity will receive the frame sent earlier. 812/10000 · 812
14 ../../principles/reliability.rst:51
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — :math:`10^3` 12/10000 · 12
14 ../../exercises/network.rst:108
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Is it possible to configure the link metrics so that the packets sent by the router located in `Los Angeles` to the routers located in respectively `New York` and `Washington` do not follow the same path ? 205/10000 · 205
14 ../../exercises/reliability.rst:31
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The bandwidth of the two directions of the link is set to `B` bits per second 77/10000 · 77
14 ../../exercises/transport.rst:128
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A network layer service guarantees that a packet will never live during more than 100 seconds inside the network. Consider a reliable connection-oriented transport protocol that places a 32 bits sequence number inside each segment. What is the maximum rate (in segments per second) at which is should sent data segments to prevent having two segments with the same sequence number inside the network ? 401/10000 · 401
14 ../../principles/sharing.rst:150
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 878/10000 · 878
14 ../../principles/transport.rst:56
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Such a conversation succeeds if both Alice and Bob speak the same language. If Alice meets Tchang who only speaks Chinese, she won't be able to ask him the current time. A conversation between humans can be more complex. For example, assume that Bob is a security guard whose duty is to only allow trusted secret agents to enter a meeting room. If all agents know a secret password, the conversation between Bob and Trudy could be as follows : 443/10000 · 443
14 ../../protocols/dns.rst:51
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The `TTL` field indicates the lifetime of the `Resource Record` in seconds. This field is set by the server that returns an answer and indicates for how long a client or a resolver can store the `Resource Record` inside its cache. A long `TTL` indicates a stable `RR`. Some companies use short `TTL` values for mobile hosts and also for popular servers. For example, a web hosting company that wants to spread the load over a pool of hundred servers can configure its nameservers to return different answers to different clients. If each answer has a small `TTL`, the clients will be forced to send DNS queries regularly. The nameserver will reply to these queries by supplying the address of the less loaded server. 716/10000 · 716
14 ../../principles/security.rst:187
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The last type of attack that we consider in this introduction are the `Denial of Service` or DoS attacks. During such an attack, the attacker generates enough packets to saturate a given service and prevent it from operating correctly. The simplest Denial of Service attack is to send more packets that the bandwidth of the link that attaches the target to the network. The target could be a single server, a company or even an entire country. If these packets all come from the same source, then the victim can identify the attacker and contact the law enforcement authorities. In practice, such denial of service attacks do not originate from a single source. The attacker usually compromises a (possibly very large) set of sources and forces them to send packets to saturate a given target. Since the attacking traffic comes from a wide range of sources, it is difficult for the victim to locate the culprit and also to counter the attack. Saturating a link is the simplest example of `Distributed Denial of Service (DDoS)` attacks. 1035/10000 · 1035
14 ../../exercises/dns.rst:45
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — What is the IPv6 address that corresponds to `www.computer-networking.info` ? Which type of DNS query does `dig` send to obtain this information ? 146/10000 · 146
14 ../../exercises/http.rst:37
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — As for the DNS, besides using software tools that implement the HTTP protocols, it can also be useful to analyze packet traces with wireshark_ . The exercises below contain simple packet traces collected with different versions of the HTTP protocol. 249/10000 · 249
14 ../../exercises/ipv6.rst:43 • ../../exercises/ipv6.rst:152
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — router ``R4`` uses address ``2001:db8:1341:34::4`` on its West interface, address ``2001:db8:1341:24::4`` on its North interface and address ``2001:db8:1341:4::4`` on its East interface 185/10000 · 185
14 ../../exercises/lan.rst:91
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Fig. 5. Will the link between `S0` and `S1` ever be used? 57/10000 · 57
14 ../../exercises/routing-policies.rst:151
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Via which provider does `AS456` receive the packets destined to ``2001:db8:caff::bb`` and ``2001:db8:cafe::aa`` ? 113/10000 · 113
14 ../../exercises/routing-protocols.rst:239
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — We can also use the packet traces that were collected by tcpdump_ to observe the packets that the OSPFv3 daemons exchange. OSPFv3 is a more complex protocol that the basic link state protocol that we have described in this book, but you should be able to understand some of these packets. The packet traces are available as :download:`/exercises/traces/ospf6-r1-trace.pcap`, :download:`/exercises/traces/ospf6-r2-trace.pcap` and :download:`/exercises/traces/ospf6-r3-trace.pcap`. Here are a few interesting packets collected on router ``r1``. 542/10000 · 542
14 ../../exercises/tcp-2.rst:80
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — At this point, the socket is ready to accept incoming TCP connections. packetdrill_ needs to inject a TCP segment in the instrumented Linux stack. This can be done with the line below. 184/10000 · 184
14 ../../exercises/trace.rst:88
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Wireshark : default window 26/10000 · 26
14 ../../protocols/bgp.rst:55
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — To understand the `customer->provider` relationship, let us consider the simple internetwork shown in the figure above. In this internetwork, `AS7` is a stub domain that is connected to one provider : `AS4`. The contract between `AS4` and `AS7` allows a host inside `AS7` to exchange packets with any host in the internetwork. To enable this exchange of packets, `AS7` must know a route towards any domain and all the domains of the internetwork must know a route via `AS4` that allows them to reach hosts inside `AS7`. From a routing perspective, the commercial contract between `AS7` and `AS4` leads to the following routes being exchanged : 643/10000 · 643