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../../protocols/tcp.rst:50
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the `RST` is used in case of problems or when an invalid segment has been received
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../../protocols/tls.rst:47
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990
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../../protocols/transport-service.rst:65
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The second transport service is the connection-oriented service. On the Internet, this service is often called the `byte-stream service` as it creates a reliable byte stream between the two applications that are linked by a transport connection. Like the datagram service, the networked applications that use the byte-stream service are identified by the host on which they run and a port number. These hosts can be identified by an address or a name. The figure below illustrates two applications that are using the byte-stream service provided by the TCP protocol on IPv6 hosts. The byte stream service provided by TCP is reliable and bidirectional.
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../../protocols/udp.rst:74
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the entire UDP segment, including its header
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../../protocols/wifi.rst:24
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11 Mbps
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../../bibliography.rst:74
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Feldmeier, D. C., `Fast software implementation of error detection codes <https://dx.doi.org/10.1109/90.477710>`_. IEEE/ACM Transactions Networking 3, 6 (Dec. 1995), 640-651.
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../../glossary.rst:24
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broadcast
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../../exercises/ex-sharing.rst:559
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How is the maximum round-trip-time influenced if the buffers of router `R1` store 10 packets ?
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../../principles/sharing.rst:133
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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.
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../../principles/security.rst:310
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A secret key encryption scheme is a perfectly reversible functions, i.e. given an encryption function `E`, there is an associated decryption function `D` such that :math:`\forall k \forall M : D(K, E(M,K))=M`.
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../../exercises/dns.rst:73
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A DNS implementation such as `dig`, and more importantly a name resolver such as bind_ or unbound_, always checks that the received DNS reply contains the same identifier as the DNS request that it sent. Why is this so important ?
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../../exercises/ipv6.rst:220
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Assuming that the following IPv6 addresses are used :
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../../exercises/lan.rst:250
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The state of switch ``s9`` is different. The output of :manpage:`brctl(8)` indicates that the root identifier is ``0003.f63545ab5f79`` which is at a distance of ``1`` from switch ``s9``. The root port on ``s9`` is port `1`, i.e. ``s9-eth1``. Two of the ports of this switch forward data packets, the root port and the ``s9-eth3`` which is a designated port. The ``s9-eth2`` port is a blocked port.
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../../exercises/routing-policies.rst:197
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``Code==0``
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../../exercises/routing-protocols.rst:274
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IPMininet_ can also be used to perform experiments with RIP. A simple script that uses RIPng is provided below.
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../../exercises/tcp-2.rst:133
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packetdrill_ injects the ``FIN`` segment and the instrumented kernel returns an acknowledgment. If packetdrill_ issues the :manpage:`close` system call, the kernel will send a ``FIN`` segment to terminate the connection. packetdrill_ injects an acknowledgment to confirm the end of the connection.
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../../protocols/bgp.rst:79
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the `export filter` that specifies, for each peering relationship, the routes that can be advertised to the neighboring domain
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../../protocols/congestion.rst:122
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Thanks to the `ECT`, `CE` and `ECE`, routers can mark packets during congestion and receivers can return the congestion information back to the TCP senders. However, these three bits are not sufficient to allow a server to reliably send the `ECE` bit to a TCP sender. TCP acknowledgments are not sent reliably. A TCP acknowledgment always contains the next expected sequence number. Since TCP acknowledgments are cumulative, the loss of one acknowledgment is recovered by the correct reception of a subsequent acknowledgment.
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../../protocols/dnssec.rst:263
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The last record introduced by DNSSEC is the `NSEC` record. It is used to authenticate a negative response returned by a DNS server. If a resolver requests a domain name that is not defined in the zone, the server replies with an error message. The designers of the original version of the DNS thought that these errors would not be very frequent and resolvers were not required to cache those negative responses. However, operational experience showed that queries for invalid domain names are more frequent than initially expected and a large fraction of the load on some servers is caused by repeated queries for invalid names. Typical examples include queries for invalid TLDs to the root DNS servers or queries caused by configuration errors [WF2003]_. Current DNS deployments allow resolvers to cache those negative answers to reduce the load on the entire DNS :rfc:`2308`.
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../../protocols/email.rst:126
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the `Message-Id:` header line is used to associate a "unique" identifier to each email. Email identifiers are usually structured like `string@domain` where `string` is a unique character string or sequence number chosen by the sender of the email and `domain` the domain name of the sender. Since domain names are unique, a host can generate globally unique message identifiers concatenating a locally unique identifier with its domain name.
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