Exit Zen
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../../protocols/ethernet.rst:287
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Security issues with Ethernet hubs and switches
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../../protocols/tcp.rst:243
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TCP reliable data transfer
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../../protocols/tls.rst:401
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In 2014, the IETF TLS working started to work on the development of version 1.3 of the TLS protocol. Their main objectives [Rescorla2015]_ for this new version were:
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../../glossary.rst:71
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a public internet, i.e. a network composed of different networks that are running :term:`IPv4` or :term:`IPv6`
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../../principles/network.rst:339
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Fragmenting packets on a per-link basis, as presented for the second solution, can minimize the transmission overhead since a packet is only fragmented on the links where fragmentation is required. Large packets can continue to be used downstream of a link that only accepts small packets. However, this reduction of the overhead comes with two drawbacks. First, fragmenting packets, potentially on all links, increases the processing time and the buffer requirements on the routers. Second, this solution leads to a longer end-to-end delay since the downstream router has to reassemble all the packet fragments before forwarding the packet.
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../../principles/reliability.rst:252
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`ETX`: `0000011` b
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../../principles/transport.rst:303
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Once the connection has been established, the service provider supplies two data streams to the communicating users. The first data stream can be used by the initiating user to send SDUs. The second data stream allows the responding user to send SDUs to the initiating user. The data streams can be organized in different ways. A first organization is the `message-mode` transfer. With the `message-mode` transfer, the service provider guarantees that one and only one `Data.indication` will be delivered to the endpoint of the data stream for each `Data.request` primitive issued by the other endpoint. The `message-mode` transfer is illustrated in the figure below. The main advantage of the `message-transfer` mode is that the recipient receives exactly the SDUs that were sent by the other user. If each SDU contains a command, the receiving user can process each command as soon as it receives a SDU.
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../../principles/sharing.rst:309
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ALOHA
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../../principles/security.rst:891
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agree on a way to encrypt the messages that they will exchange
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../../exercises/ipv6.rst:696
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To help students to start using IPMininet, `Mathieu Jadin <https://inl.info.ucl.ac.be/mjadin.html>`_ has created a Vagrant box that launches a Ubuntu virtual machine with all the required software. See https://ipmininet.readthedocs.io/en/latest/install.html for additional information.
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../../exercises/routing-protocols.rst:1066
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Draw the network and try to predict how it will react to a shutdown of any of the customer-provider links ?
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../../protocols/bgp.rst:298
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The first solution is the most frequent. Advertising routes learned from an intradomain routing protocol is not recommended, this is because if the route flaps [#fflap]_, this would cause a large number of BGP messages being exchanged in the global Internet.
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../../protocols/email.rst:238
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U
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../../protocols/ethernet.rst:336
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the `identifier` of the switch that sent the `BPDU` (`T`)
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../../protocols/http.rst:391
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The third and widely adopted solution are HTTP cookies. HTTP cookies were initially developed as a private extension by Netscape_. They are now part of the standard :rfc:`6265`. In a nutshell, a cookie is a short string that is chosen by a server to represent a given client. Two HTTP headers are used : `Cookie:` and `Set-Cookie:`. When a server receives an HTTP request from a new client (i.e. an HTTP request that does not contain the `Cookie:` header), it generates a cookie for the client and includes it in the `Set-Cookie:` header of the returned HTTP response. The `Set-Cookie:` header contains several additional parameters including the domain names for which the cookie is valid. The client stores all received cookies on disk and every time it sends an HTTP request, it verifies whether it already knows a cookie for this domain. If so, it attaches the `Cookie:` header to the HTTP request. This is illustrated in the figure below with HTTP 1.1, but cookies also work with HTTP 1.0.
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../../protocols/ipv6.rst:291
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Finally, :rfc:`4291` defines the structure of the IPv6 multicast addresses [#fmultiiana]_. This structure is depicted in the figure below.
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../../protocols/ethernet.rst:289
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From a security perspective, Ethernet hubs have the same drawbacks as the older coaxial cable. A host attached to a hub will be able to capture all the frames exchanged between any pair of hosts attached to the same hub. Ethernet switches are much better from this perspective thanks to the selective forwarding, a host will usually only receive the frames destined to itself as well as the multicast, broadcast and unknown frames. However, this does not imply that switches are completely secure. There are, unfortunately, attacks against Ethernet switches. From a security perspective, the `MAC address table` is one of the fragile elements of an Ethernet switch. This table has a fixed size. Some low-end switches can store a few tens or a few hundreds of addresses while higher-end switches can store tens of thousands of addresses or more. From a security point of view, a limited resource can be the target of Denial of Service attacks. Unfortunately, such attacks are also possible on Ethernet switches. A malicious host could overflow the `MAC address table` of the switch by generating thousands of frames with random source addresses. Once the `MAC address table` is full, the switch needs to broadcast all the frames that it receives. At this point, an attacker will receive unicast frames that are not destined to its address. The ARP attack discussed in the previous chapter could also occur with Ethernet switches [Vyncke2007]_. Recent switches implement several types of defenses against these attacks, but they need to be carefully configured by the network administrator. See [Vyncke2007]_ for a detailed discussion on security issues with Ethernet switches.
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../../protocols/tcp.rst:245
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The original TCP data transfer mechanisms were defined in :rfc:`793`. Based on the experience of using TCP on the growing global Internet, this part of the TCP specification has been updated and improved several times, always while preserving the backward compatibility with older TCP implementations. In this section, we review the main data transfer mechanisms used by TCP.
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../../protocols/tls.rst:403
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simplify the design by removing unused or unsafe protocol features
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../../glossary.rst:72
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internet
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