Exit Zen
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../../exercises/transport.rst:142
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DATA segments contain a sequence number that is incremented for each DATA segment transmitted
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../../principles/naming.rst:112
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To retrieve the mapping for host `h2.dom`, a client sends its query to the name server that is responsible for domain `.dom`. The name server directly answers the query. To retrieve a mapping for `h3.a.sdom1.dom` a DNS client first sends a query to the name server that is responsible for the `.dom` domain. This nameserver returns the nameserver that is responsible for the `sdom1.dom` domain. This nameserver can now be contacted to obtain the nameserver that is responsible for the `a.sdom1.dom` domain. This nameserver can be contacted to retrieve the mapping for the `h3.a.sdom1.dom` name. Thanks to this structure, it is possible for a DNS client to obtain the mapping of any host inside the `.dom` domain or any of its subdomains. To ensure that any DNS client will be able to resolve any fully qualified domain name, there are special nameservers that are responsible for the root of the domain name hierarchy. These nameservers are called :term:`root nameserver`.
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../../principles/network.rst:87
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the network layer address of the destination host
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../../principles/reliability.rst:54
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:math:`10^{12}`
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../../principles/transport.rst:50
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Alice : `3.1415`
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../../protocols/dns.rst:67
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Reverse DNS
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../../exercises/reliability.rst:44
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Same question when using selective repeat instead of go-back-n. Note that the answer is not necessarily the same.
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../../exercises/network.rst:180
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Is it possible to achieve these paths and if so what are the required forwarding tables ?
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../../exercises/sockets.rst:213
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This function is now using the ``recvfrom`` system call that will also provide the address of the peer who sent the message. As addresses are generic and can have different sizes, ``recvfrom`` also tells us the size of the address that it has written.
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../../exercises/transport.rst:144
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Some transport protocols use 32 bits sequence numbers while others use 64 bits sequence number. What are the advantages and drawbacks of each approach ?
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../../principles/naming.rst:114
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Each root nameserver maintains the list [#froot]_ of all the nameservers that are responsible for each of the top-level domain names and their addresses [#frootv6]_. All root nameservers cooperate and provide the same answers. By querying any of the root nameservers, a DNS client can obtain the nameserver that is responsible for any top-level-domain name. From this nameserver, it is possible to resolve any domain name.
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../../principles/network.rst:88
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its own network layer address
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../../principles/reliability.rst:59
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To understand some of the principles behind the physical transmission of information, let us consider the simple case of an electrical wire that is used to transmit bits. Assume that the two communicating hosts want to transmit one thousand bits per second. To transmit these bits, the two hosts can agree on the following rules :
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../../principles/transport.rst:51
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Bob : `This is not the correct password.`
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../../protocols/dns.rst:69
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The DNS is mainly used to find the address that corresponds to a given name. However, it is sometimes useful to obtain the name that corresponds to an IP address. This done by using the `PTR` (`pointer`) `RR`. The `RData` part of a `PTR` `RR` contains the name while the `Name` part of the `RR` contains the IP address encoded in the `in-addr.arpa` domain. IPv4 addresses are encoded in the `in-addr.arpa` by reversing the four digits that compose the dotted decimal representation of the address. For example, consider IPv4 address `192.0.2.11`. The hostname associated to this address can be found by requesting the `PTR` `RR` that corresponds to `11.2.0.192.in-addr.arpa`. A similar solution is used to support IPv6 addresses :rfc:`3596`, but slightly more complex given the length of the IPv6 addresses. For example, consider IPv6 address `2001:1890:123a::1:1e`. To obtain the name that corresponds to this address, we need first to convert it in a reverse dotted decimal notation : `e.1.0.0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.a.3.2.1.0.9.8.1.1.0.0.2`. In this notation, each character between dots corresponds to one nibble, i.e. four bits. The low-order byte (`e`) appears first and the high order (`2`) last. To obtain the name that corresponds to this address, one needs to append the `ip6.arpa` domain name and query for `e.1.0.0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.a.3.2.1.0.9.8.1.1.0.0.2.ip6.arpa`. In practice, tools and libraries do the conversion automatically and the user does not need to worry about it.
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../../exercises/reliability.rst:50
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Practice
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../../exercises/network.rst:182 • ../../exercises/network.rst:214
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Same question with virtual circuits.
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../../exercises/sockets.rst:216
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``connect``: connecting a socket to a remote address
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../../exercises/transport.rst:146
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Consider a transport protocol that provides the bytestream service and uses 32 bits sequence number to represent the position of the first byte of the payload of DATA segments in the bytestream. How would you modify this protocol so that it can provide a message-mode service ? Consider first short messages that always fit inside a single segment. In a second step, discuss how you could support messages of unlimited size.
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../../principles/naming.rst:117
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To be able to contact the root nameservers, each DNS client must know their addresses. This implies, that DNS clients must maintain an up-to-date list of the addresses of the root nameservers. Without this list, it is impossible to contact the root nameservers. Forcing all Internet hosts to maintain the most recent version of this list would be difficult from an operational point of view. To solve this problem, the designers of the DNS introduced a special type of DNS server : the DNS resolvers. A :term:`resolver` is a server that provides the name resolution service for a set of clients. A network usually contains a few resolvers. Each host in these networks is configured to send all its DNS queries via one of its local resolvers. These queries are called `recursive queries` as the :term:`resolver` must recursively send requests through the hierarchy of nameservers to obtain the `answer`.
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