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../../principles/referencemodels.rst:40
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the Physical layer may deliver `fewer` bits to the receiver than the bits sent by the sender
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../../principles/network.rst:68
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To understand the key principles behind the operation of a network, let us analyze all the operations that need to be performed to allow host `A` in the above network to send one byte to host `B`. Thanks to the datalink layer used above the `A-R1` link, host `A` can easily send a byte to router `R1` inside a frame. However, upon reception of this frame, router `R1` needs to understand that this byte is destined to host `B` and not to itself. This is the objective of the network layer.
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../../principles/reliability.rst:49
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Bits per second
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../../principles/transport.rst:32
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Bob : `11:55`
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../../protocols/dns.rst:48
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DNS Resource Records
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../../principles/security.rst:155
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Eavesdropping and pervasive monitoring are not the only possible attacks against a network. Another type of attacker is the active attacker. In the literature, these attacks are often called `Man in the middle` or `MITM` attacks. Such attacks occur when one user, let us call him `Mallory`, has managed to configure the network so that he can both capture and modify the packets exchanged by two users. The simplest scenario is when Mallory controls a router that is on the path used by both Alice and Bob. For example, Alice could be connected to a WiFi access router controlled by Mallory and Bob would be a regular server on the Internet.
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../../exercises/dns.rst:41
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What are the IP addresses of the resolvers that the `dig` implementation you are using relies on [#fdig]_ ?
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../../exercises/email.rst:27
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On Unix hosts, a subset of the port assignments is often placed in `/etc/services`.
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../../exercises/http.rst:33
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Some websites are reachable over both IPv4 and IPv6 while others are only reachable over IPv4 [#fv6only]_. You can use the `-6` (resp. `-4`) option to force curl_ to only use IPv6 (resp. IPv4). Verify that `www.computer-networking.info` is reachable over IPv6 and IPv4 and then check whether your university website already supports IPv6.
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../../exercises/ipv6.rst:41
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router ``R2`` uses address ``2001:db8:1341:12::2`` on its West interface, address ``2001:db8:1341:23::2`` on its South-West interface and address ``2001:db8:1341:24::2`` on its South interface.
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../../exercises/lan.rst:83
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Fig. 4. Can `H0` and `H1` communicate ?
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../../exercises/routing-policies.rst:141
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Should `AS123` change its configuration ?
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../../exercises/routing-protocols.rst:175
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The ``show ipv6 ospf6`` command reports the general state of the OSPFv3 daemon. The ``show ipv6 ospf6 neighbor`` command reports the state of the connected neighbors.
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../../exercises/tcp-2.rst:63
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The ``0`` indicates that the system call must be issued immediately. packetdrill_ then executes the system call and verifies that it returns ``3```. If yes, the processing continues. Otherwise the script stops and indicates an error.
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../../exercises/trace.rst:79
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tcpdump_ can provide more detailed information about the packets by using the `-v` or `-vv` option.
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../../protocols/bgp.rst:47
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The first category of peering relationship is the `customer->provider` relationship. Such a relationship is used when a customer domain pays an Internet Service Provider to be able to exchange packets with the global Internet over an interdomain link. A similar relationship is used when a small Internet Service Provider pays a larger Internet Service Provider to exchange packets with the global Internet.
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../../protocols/congestion.rst:43
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Evaluation of the TCP congestion window when the network is lightly congested
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../../protocols/dnssec.rst:144
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To cope with these security threats and improve the security of the DNS, the IETF has defined several extensions that are known as DNSSEC. DNSSEC exploits public-key cryptography to authenticate the content of the DNS records that are sent by DNS servers and resolvers. DNSEC is defined in three main documents :rfc:`4033`, :rfc:`4034`, :rfc:`4035`. With DNSSEC, each DNS zone uses one public-private key pair. This key pair is only used to sign and authenticate DNS records. The DNS records are not encrypted and DNSSEC does not provide any confidentiality. Other DNS extensions are being developed to ensure the confidentiality of the information exchanged between a client and its resolvers :rfc:`7626`. Some of these extensions exchange DNS records over a TLS session which provides the required confidentiality, but they are not yet deployed and outside the scope of this chapter.
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../../protocols/email.rst:61
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the `body` that contains the message itself.
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../../protocols/ethernet.rst:81
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The Ethernet frame format shown above is specified in [DIX]_. This is the format used to send both IPv4 :rfc:`894` and IPv6 packets :rfc:`2464`. After the publication of [DIX]_, the Institute of Electrical and Electronic Engineers (IEEE) began to standardize several Local Area Network technologies. IEEE worked on several LAN technologies, starting with Ethernet, Token Ring and Token Bus. These three technologies were completely different, but they all agreed to use the 48 bits MAC addresses specified initially for Ethernet [IEEE802]_ . While developing its Ethernet standard [IEEE802.3]_, the IEEE 802.3 working group was confronted with a problem. Ethernet mandated a minimum payload size of 46 bytes, while some companies were looking for a LAN technology that could transparently transport short frames containing only a few bytes of payload. Such a frame can be sent by an Ethernet host by padding it to ensure that the payload is at least 46 bytes long. However since the Ethernet header [DIX]_ does not contain a length field, it is impossible for the receiver to determine how many useful bytes were placed inside the payload field. To solve this problem, the IEEE decided to replace the `Type` field of the Ethernet [DIX]_ header with a length field [#ftypelen]_. This `Length` field contains the number of useful bytes in the frame payload. The payload must still contain at least 46 bytes, but padding bytes are added by the sender and removed by the receiver. In order to add the `Length` field without significantly changing the frame format, IEEE had to remove the `Type` field. Without this field, it is impossible for a receiving host to identify the type of network layer packet inside a received frame. To solve this new problem, IEEE developed a completely new sublayer called the Logical Link Control [IEEE802.2]_. Several protocols were defined in this sublayer. One of them provided a slightly different version of the `Type` field of the original Ethernet frame format. Another contained acknowledgments and retransmissions to provide a reliable service... In practice, [IEEE802.2]_ is never used to support IP in Ethernet networks. The figure below shows the official [IEEE802.3]_ frame format.
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