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../../protocols/bgp.rst:291
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Origin of the routes advertised by a BGP router
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../../protocols/email.rst:236
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../../protocols/ethernet.rst:329
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Switches running the `Spanning Tree Protocol` exchange `BPDUs`. These `BPDUs` are always sent as frames with destination MAC address as the `ALL_BRIDGES` reserved multicast MAC address. Each switch has a unique 64 bit `identifier`. To ensure uniqueness, the lower 48 bits of the identifier are set to the unique MAC address allocated to the switch by its manufacturer. The high order 16 bits of the switch identifier can be configured by the network administrator to influence the topology of the spanning tree. The default value for these high order bits is 32768.
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../../protocols/http.rst:383
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As illustrated above, a client can send several HTTP requests over the same persistent TCP connection. However, it is important to note that all of these HTTP requests are considered to be independent by the server. Each HTTP request must be self-contained. This implies that each request must include all the header lines that are required by the server to understand the request. The independence of these requests is one of the key design choices of HTTP. As a consequence of this design choice, when a server processes a HTTP request, it does not use any other information than what is contained in the request itself. This explains why the client adds its `User-Agent:` header in all of the HTTP requests that it sends over the persistent TCP connection.
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../../protocols/ipv6.rst:259
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All IPv6 hosts have several addresses
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../../protocols/ethernet.rst:255
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Operation of Ethernet switches
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../../protocols/tcp.rst:233
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The robustness principle
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../../protocols/tls.rst:385
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Measurement studies that analyzed the evolution of TLS over the years have identified several important changes in the TLS ecosystem [KRA2018]_. First, the preferred cryptographic algorithms have changed. While RC4 was used by 60% of the connections in 2012, its usage has dropped since 2015. AEA started to be deployed in 2013 and is now used for more than 90% of the connections. The deployed versions of TLS have also changed. TLS 1.0 and TLS 1.1 are now rarely used. The deployment of TLS 1.2 started in 2013 and reached 70% of the connections in 2015. Version 1.3 of TLS, that is described below, is also widely deployed.
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../../principles/network.rst:332
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Each of the packet fragments is a valid packet that contains a header with the source (host `A`) and destination (host `B`) addresses. When router `R2` receives a packet fragment, it treats this packet as a regular packet and forwards it to its final destination (host `B`). Host `B` reassembles the received fragments.
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../../principles/reliability.rst:249
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`LF` : `0001010` b
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../../principles/transport.rst:241
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The establishment of a connection can be modeled by using four primitives : `Connect.request`, `Connect.indication`, `Connect.response` and `Connect.confirm`. The `Connect.request` primitive is used to request the establishment of a connection. The main parameter of this primitive is the `address` of the destination user. The service provider delivers a `Connect.indication` primitive to inform the destination user of the connection attempt. If it accepts to establish a connection, it responds with a `Connect.response` primitive. At this point, the connection is considered to be established and the destination user can start sending SDUs over the connection. The service provider processes the `Connect.response` and will deliver a `Connect.confirm` to the user who initiated the connection. The delivery of this primitive terminates the connection establishment phase. At this point, the connection is considered to be open and both users can send SDUs. A successful connection establishment is illustrated below.
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../../principles/security.rst:860
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A possible protocol could then be the following. Alice sends :math:`Cert(Alice_{pub},Ted)`. Bob replies with a random nonce.
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../../exercises/ipv6.rst:675
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We can now create the hosts and the routers
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../../exercises/routing-protocols.rst:1016
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When this network is launched, `ping6all` reports connectivity problems. Hosts `h1` and `h4` cannot exchange packets. Can you fix the problem by changing the routing policy used on only one interdomain link ? Justify your answer
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../../protocols/bgp.rst:293
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A frequent practical question about the operation of BGP is how a BGP router decides to originate or advertise a route for the first time. In practice, this occurs in two situations :
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../../protocols/email.rst:238 • ../../protocols/email.rst:240
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../../protocols/ethernet.rst:331
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The switches exchange `BPDUs` to build the spanning tree. Intuitively, the spanning tree is built by first selecting the switch with the smallest `identifier` as the root of the tree. The branches of the spanning tree are then composed of the shortest paths that allow all of the switches that compose the network to be reached. The `BPDUs` exchanged by the switches contain the following information :
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../../protocols/http.rst:385
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However, in practice, some servers want to provide content tuned for each user. For example, some servers can provide information in several languages. Other servers want to provide advertisements that are targeted to different types of users. To do this, servers need to maintain some information about the preferences of each user and use this information to produce content matching the user's preferences. HTTP contains several mechanisms to solve this problem. We discuss three of them below.
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../../protocols/ipv6.rst:261
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An important consequence of the IPv6 unicast addressing architecture and the utilization of link-local addresses is that each IPv6 host has several IPv6 addresses. This implies that all IPv6 stacks must be able to handle multiple IPv6 addresses.
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../../protocols/ethernet.rst:261
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One of the selling points of Ethernet networks is that, thanks to the utilization of 48 bits MAC addresses, an Ethernet LAN is plug and play at the datalink layer. When two hosts are attached to the same Ethernet segment or hub, they can immediately exchange Ethernet frames without requiring any configuration. It is important to retain this plug and play capability for Ethernet switches as well. This implies that Ethernet switches must be able to build their MAC address table automatically without requiring any manual configuration. This automatic configuration is performed by the `MAC address learning` algorithm that runs on each Ethernet switch. This algorithm extracts the source address of the received frames and remembers the port over which a frame from each source Ethernet address has been received. This information is inserted into the MAC address table that the switch uses to forward frames. This allows the switch to automatically learn the ports that it can use to reach each destination address, provided that this host has previously sent at least one frame. This is not a problem since most upper layer protocols use acknowledgments at some layer and thus even an Ethernet printer sends Ethernet frames as well.
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