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../../protocols/bgp.rst:62
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Coming back to the figure above, `AS4` advertises to its two providers `AS1` and `AS2` its own prefixes and the routes learned from its customer, `AS7`. On the other hand, `AS4` advertises to `AS7` all the routes that it knows.
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../../protocols/congestion.rst:100
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In today's Internet, congestion is controlled by regularly sending packets at a higher rate than the network capacity. These packets fill the buffers of the routers and are eventually discarded. But shortly after, TCP senders retransmit packets containing exactly the same data. This is potentially a waste of resources since these successive retransmissions consume resources upstream of the router that discards the packets. Packet losses are not the only signal to detect congestion inside the network. An alternative is to allow routers to explicitly indicate their current level of congestion when forwarding packets. This approach was proposed in the late 1980s [RJ1995]_ and used in some networks. Unfortunately, it took almost a decade before the Internet community agreed to consider this approach. In the mean time, a large number of TCP implementations and routers were deployed on the Internet.
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../../protocols/dnssec.rst:176
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The simplest way to understand the operation of DNSSEC is to rely on a simple example. Let us consider the `example.org` domain and assume that Alice wants to retrieve the `AAAA` record for `www.example.org` using DNSSEC.
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../../protocols/email.rst:105
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the `To:` header line contains the email addresses of the primary recipients of the message [#fto]_. Several addresses can be separated by using commas.
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../../protocols/ethernet.rst:99
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The first property is a consequence of the utilization of CSMA/CD. The second property is a consequence of the physical organization of the Ethernet network as a shared bus. These two properties are important and all revisions to the Ethernet technology have preserved them.
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../../protocols/http.rst:91
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The first URI corresponds to a document named `rfc3986.html` that is stored on the server named `tools.ietf.org` and can be accessed by using the `http` protocol on its default port. The second URI corresponds to an email message, with subject `current-issue`, that will be sent to user `infobot` in domain `example.com`. The `mailto:` URI scheme is defined in :rfc:`2368`. The third URI references the portion `BaseHTTPServer.BaseHTTPRequestHandler` of the document `basehttpserver.html` that is stored in the `library` directory on the `docs.python.org` server. This document can be retrieved by using the `http` protocol. The query parameter `highlight=http` is associated to this URI. The fourth example is a server that operates the telnet_ protocol, uses IPv6 address `2001:db8:3080:3::2` and is reachable on port 2323. The last URI is somewhat special. Most users will assume that it corresponds to a document stored on the `cnn.example.com` server. However, to parse this URI, it is important to remember that the `@` character is used to separate the user name from the host name in the authorization part of a URI. This implies that the URI points to a document named `top_story.htm` on the host having IPv4 address `10.0.0.1`. The document will be retrieved by using the `ftp` protocol with the user name set to `cnn.example.com&story=breaking_news`.
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../../protocols/http2.rst:139
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However, as explained in :rfc:`7230`, there is one important limitation to `pipelining`. It can only be used to serve HTTP requests that are idempotent, i.e. none of the requests must depend on any of the previous requests in the pipeline. It turned out that it was difficult for web browsers to correctly support this requirement and very few of them have implemented `pipelining` [#fpipelining]_.
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../../protocols/ipv6.rst:96
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The IPv6 header has a simple format that can easily be parsed by hardware devices
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../../protocols/ethernet.rst:14
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The third decision was the frame format. The experimental 3 Mbps Ethernet network built at Xerox used short frames containing 8 bit source and destination addresses fields, a 16 bit type indication, up to 554 bytes of payload and a 16 bit CRC. Using 8 bit addresses was suitable for an experimental network, but it was clearly too small for commercial deployments. Although the initial Ethernet specification [DIX]_ only allowed up to 1024 hosts on an Ethernet network, it also recommended three important changes compared to the networking technologies that were available at that time. The first change was to require each host attached to an Ethernet network to have a globally unique datalink layer address. Until then, datalink layer addresses were manually configured on each host. [DP1981]_ went against that state of the art and noted "`Suitable installation-specific administrative procedures are also needed for assigning numbers to hosts on a network. If a host is moved from one network to another it may be necessary to change its host number if its former number is in use on the new network. This is easier said than done, as each network must have an administrator who must record the continuously changing state of the system (often on a piece of paper tacked to the wall !). It is anticipated that in future office environments, hosts locations will change as often as telephones are changed in present-day offices.`" The second change introduced by Ethernet was to encode each address as a 48 bits field [DP1981]_. 48 bit addresses were huge compared to the networking technologies available in the 1980s, but the huge address space had several advantages [DP1981]_ including the ability to allocate large blocks of addresses to manufacturers. Eventually, other LAN technologies opted for 48 bits addresses as well [IEEE802]_ . The third change introduced by Ethernet was the definition of `broadcast` and `multicast` addresses. The need for `multicast` Ethernet was foreseen in [DP1981]_ and thanks to the size of the addressing space it was possible to reserve a large block of multicast addresses for each manufacturer.
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../../protocols/routing.rst:60
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The first RIP implementations sent their distance vector exactly every 30 seconds. This worked well in most networks, but some researchers noticed that routers were sometimes overloaded because they were processing too many distance vectors at the same time [FJ1994]_. They collected packet traces in these networks and found that after some time the routers' timers became synchronized, i.e. almost all routers were sending their distance vectors at almost the same time. This synchronization of the transmission times of the distance vectors caused an overload on the routers' CPU but also increased the convergence time of the protocol in some cases. This was mainly due to the fact that all routers set their timers to the same expiration time after having processed the received distance vectors. `Sally Floyd`_ and `Van Jacobson`_ proposed in [FJ1994]_ a simple solution to solve this synchronization problem. Instead of advertising their distance vector exactly after 30 seconds, a router should send its next distance vector after a delay chosen randomly in the [15,45] interval :rfc:`2080`. This randomization of the delays prevents the synchronization that occurs with a fixed delay and is now a recommended practice for protocol designers.
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../../protocols/rpc.rst:65
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XDR also supports the definition of unions, structures, ... Additional details are provided in :rfc:`1832`.
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../../protocols/ssh.rst:148
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the client can recompute :math:`K=A^{b} \mod p` and verify the signature provided by the server
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../../protocols/tcp.rst:44
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the `sequence number` (32 bits), `acknowledgment number` (32 bits) and `window` (16 bits) fields are used to provide a reliable data transfer, using a window-based protocol. In a TCP bytestream, each byte of the stream consumes one sequence number. Their usage is described in more detail in section :ref:`TCPReliable`
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../../protocols/tls.rst:46
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HTTP
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../../protocols/transport-service.rst:56
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IPv6 addresses often contain a long sequence of bits set to `0`. In this case, a compact notation has been defined. With this notation, `::` is used to indicate one or more groups of 16 bits blocks containing only bits set to `0`. For example,
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../../protocols/udp.rst:62
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the registered port numbers (officially 1024 <= port < 49152)
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../../protocols/wifi.rst:23
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23 Mbps
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../../bibliography.rst:64
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Wikipedia, `Dijkstra's algorithm <https://en.wikipedia.org/wiki/Dijkstra's_algorithm>`_
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../../glossary.rst:228
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Asynchronous Transfer Mode
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../../exercises/ex-sharing.rst:399
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Suppose now that host A uses a window of three segments and sends these three segments immediately. The segments will be queued in the router before being transmitted on the output link and delivered to their destination. The destination will reply with a short acknowledgment segment. A possible visualization of this exchange of packets is represented in the figure below. We assume for this figure that the router marks the packets to indicate congestion as soon as its buffer is non-empty when its receives a packet on its input link. In the figure, a `(c)` sign is added to each packet to indicate that it has been explicitly marked.
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