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cnp3-ebook / principles/naming — English

Names provide a lot of flexibility compared to addresses. For the network, they play a similar role as variables in programming languages. No programmer using a high-level programming language would consider using hardcoded values instead of variables. For the same reasons, all networked applications should depend on names and avoid dealing with addresses as much as possible.
Names provide a lot of flexibility compared to addresses. For the network, they play a similar role as variables in programming languages. No programmer using a high-level programming language would consider using hardcoded values instead of variables. For the same reasons, all networked applications should depend on names and avoid dealing with addresses as much as possible.
a year ago
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cnp3-ebook / principles/naming — English

Mapping a single name onto a set of addresses allows popular servers to dynamically scale. There are also benefits in mapping multiple names, possibly a large number of them, onto a single address. Consider the case of information servers run by individuals or SMEs. Some of these servers attract only a few clients per day. Using a single physical server for each of these services would be a waste of resources. A better approach is to use a single server for a set of services that are all identified by different names. This enables service providers to support a large number of servers processes, identified by different names, onto a single physical server. If one of these server processes becomes very popular, it will be possible to map its name onto a set of addresses to be able to sustain the load. There are some deployments where this mapping is done dynamically in function of the load.
Mapping a single name onto a set of addresses allows popular servers to dynamically scale. There are also benefits in mapping multiple names, possibly a large number of them, onto a single address. Consider the case of information servers run by individuals or SMEs. Some of these servers attract only a few clients per day. Using a single physical server for each of these services would be a waste of resources. A better approach is to use a single server for a set of services that are all identified by different names. This enables service providers to support a large number of servers processes, identified by different names, onto a single physical server. If one of these server processes becomes very popular, it will be possible to map its name onto a set of addresses to be able to sustain the load. There are some deployments where this mapping is done dynamically in function of the load.
a year ago
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cnp3-ebook / principles/naming — English

Using names solves these problems and provides additional benefits. If the clients are configured with the name of the server, they will query the name service before contacting the server. The name service will resolve the name into the corresponding address. If a server process needs to move from one physical server to another, it suffices to update the name to address mapping on the name service to allow all clients to connect to the new server. The name service also enables the servers to better sustain the load. Assume a very popular server which is accessed by millions of users. This service cannot be provided by a single physical server due to performance limitations. Thanks to the utilization of names, it is possible to scale this service by mapping a given name to a set of addresses. When a client queries the name service for the server's name, the name service returns one of the addresses in the set. Various strategies can be used to select one particular address inside the set of addresses. A first strategy is to select a random address in the set. A second strategy is to maintain information about the load on the servers and return the address of the less loaded server. Note that the list of server addresses does not need to remain fixed. It is possible to add and remove addresses from the list to cope with load fluctuations. Another strategy is to infer the location of the client from the name request and return the address of the closest server.
Using names solves these problems and provides additional benefits. If the clients are configured with the name of the server, they will query the name service before contacting the server. The name service will resolve the name into the corresponding address. If a server process needs to move from one physical server to another, it suffices to update the name to address mapping on the name service to allow all clients to connect to the new server. The name service also enables the servers to better sustain the load. Assume a very popular server which is accessed by millions of users. This service cannot be provided by a single physical server due to performance limitations. Thanks to the utilization of names, it is possible to scale this service by mapping a given name to a set of addresses. When a client queries the name service for the server's name, the name service returns one of the addresses in the set. Various strategies can be used to select one particular address inside the set of addresses. A first strategy is to select a random address in the set. A second strategy is to maintain information about the load on the servers and return the address of the less loaded server. Note that the list of server addresses does not need to remain fixed. It is possible to add and remove addresses from the list to cope with load fluctuations. Another strategy is to infer the location of the client from the name request and return the address of the closest server.
a year ago
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cnp3-ebook / principles/naming — English

In addition to being more human friendly, using names instead of addresses inside applications has several important benefits. To understand them, let us consider a popular application that provides information stored on servers. This application involves clients and servers. The server provides information upon requests from client processes. A first deployment of this application would be to rely only on addresses. In this case, the server process would be installed on one host and the clients would connect to this server to retrieve information. Such a deployment has several drawbacks :
In addition to being more human friendly, using names instead of addresses inside applications has several important benefits. To understand them, let us consider a popular application that provides information stored on servers. This application involves clients and servers. The server provides information upon requests from client processes. A first deployment of this application would be to rely only on addresses. In this case, the server process would be installed on one host and the clients would connect to this server to retrieve information. Such a deployment has several drawbacks :
a year ago
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cnp3-ebook / principles/naming — English

The possibility of using all Unicode characters to create domain names opened a new form of attack called the `homograph attack <https://en.wikipedia.org/wiki/IDN_homograph_attack>`_. This attack occurs when two character strings or domain names are visually similar but do not correspond to the same server. A simple example is https://G00GLE.COM and https://GOOGLE.COM. These two URLs are visually close but they correspond to different names (the first one does not point to a valid server [#fg00gle]_). With other Unicode characters, it is possible to construct domain names are visually equivalent to existing ones. See [Zhe2017]_ for additional details on this attack.
The possibility of using all Unicode characters to create domain names opened a new form of attack called the `homograph attack <https://en.wikipedia.org/wiki/IDN_homograph_attack>`_. This attack occurs when two character strings or domain names are visually similar but do not correspond to the same server. A simple example is https://G00GLE.COM and https://GOOGLE.COM. These two URLs are visually close but they correspond to different names (the first one does not point to a valid server [#fg00gle]_). With other Unicode characters, it is possible to construct domain names are visually equivalent to existing ones. See [Zhe2017]_ for additional details on this attack.
a year ago
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cnp3-ebook / principles/naming — English

In the early days of the Internet, only a few hosts (mainly minicomputers) were connected to the network. The most popular applications were :term:`remote login` and file transfer. By 1983, there were already five hundred hosts attached to the Internet [Zakon]_. Each of these hosts were identified by a unique address. Forcing human users to remember the addresses of the hosts that they wanted to use was not user-friendly. Humans prefer to remember names, and use them when needed. Using names as aliases for addresses is a common technique in Computer Science. It simplifies the development of applications and allows the developer to ignore the low level details. For example, by using a programming language instead of writing machine code, a developer can write software without knowing whether the variables that it uses are stored in memory or inside registers.
In the early days of the Internet, only a few hosts (mainly minicomputers) were connected to the network. The most popular applications were :term:`remote login` and file transfer. By 1983, there were already five hundred hosts attached to the Internet [Zakon]_. Each of these hosts were identified by a unique address. Forcing human users to remember the addresses of the hosts that they wanted to use was not user-friendly. Humans prefer to remember names, and use them when needed. Using names as aliases for addresses is a common technique in Computer Science. It simplifies the development of applications and allows the developer to ignore the low level details. For example, by using a programming language instead of writing machine code, a developer can write software without knowing whether the variables that it uses are stored in memory or inside registers.
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cnp3-ebook / exercises/transport — English

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cnp3-ebook / exercises/transport — English

Which are the mechanisms that should be included in a transport protocol providing an unreliable connectionless transport service that can detect transmission errors, but not correct them ?
Which are the mechanisms that should be included in a transport protocol providing an unreliable connectionless transport service that can detect transmission errors, but not correct them ?
a year ago
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cnp3-ebook / exercises/transport — English

Multiple choices questions
Multiple choices questions
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cnp3-ebook / exercises/intro — English

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cnp3-ebook / exercises/sockets — English

File locale/pot/exercises/sockets.pot was added. a year ago
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cnp3-ebook / exercises/sockets — English

If you want to observe the packets exchanged over the network, use a packet dissector such as `wireshark`_ or `tcpdump`_, listen the loopback interface (``lo``) and filter UDP packets using port 10000 (``udp.port==10000`` in `wireshark`_, ``udp port 10000`` with `tcpdump`_).
If you want to observe the packets exchanged over the network, use a packet dissector such as `wireshark`_ or `tcpdump`_, listen the loopback interface (``lo``) and filter UDP packets using port 10000 (``udp.port==10000`` in `wireshark`_, ``udp port 10000`` with `tcpdump`_).
a year ago
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cnp3-ebook / exercises/sockets — English

As an example, here is what you could have to invoke your programs.
As an example, here is what you could have to invoke your programs.
a year ago
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cnp3-ebook / exercises/sockets — English

to wrap the ``recv_and_handle_message`` server function in a ``server`` executable, similarly to what you have done with the ``client`` executable.
to wrap the ``recv_and_handle_message`` server function in a ``server`` executable, similarly to what you have done with the ``client`` executable.
a year ago
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cnp3-ebook / exercises/sockets — English

to wrap the ``create_and_send_message`` in a ``client`` executable that can parse user arguments (the ``getopt(3)`` function might help) and appropriately call the wrapped function;
to wrap the ``create_and_send_message`` in a ``client`` executable that can parse user arguments (the ``getopt(3)`` function might help) and appropriately call the wrapped function;
a year ago
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cnp3-ebook / exercises/sockets — English

During this course, you will be asked to implement a transport protocol running on Linux devices. To prepare yourself, try to implement the protocol described in the above tasks on your Linux personal machine. If you did these exercises correctly, most of your answers can be used as it (do not forget to include the required header files). In addition to the previously produced code, you will need
During this course, you will be asked to implement a transport protocol running on Linux devices. To prepare yourself, try to implement the protocol described in the above tasks on your Linux personal machine. If you did these exercises correctly, most of your answers can be used as it (do not forget to include the required header files). In addition to the previously produced code, you will need
a year ago

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