Exit Zen
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../../protocols/http.rst:443
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Footnotes
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../../protocols/ipv6.rst:321
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IPv6 packet format
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../../protocols/ethernet.rst:303
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When all switches boot, their `MAC address table` is empty. Assume that host `A` sends a frame towards host `C`. Upon reception of this frame, switch1 updates its `MAC address table` to remember that address `A` is reachable via its West port. As there is no entry for address `C` in switch1's `MAC address table`, the frame is forwarded to both switch2 and switch3. When switch2 receives the frame, its updates its `MAC address table` for address `A` and forwards the frame to host `C` as well as to switch3. switch3 has thus received two copies of the same frame. As switch3 does not know how to reach the destination address, it forwards the frame received from switch1 to switch2 and the frame received from switch2 to switch1... The single frame sent by host `A` will be continuously duplicated by the switches until their `MAC address table` contains an entry for address `C`. Quickly, all the available link bandwidth will be used to forward all the copies of this frame. As Ethernet does not contain any `TTL` or `HopLimit`, this loop will never stop.
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../../protocols/tcp.rst:250
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`acknowledgment number`. TCP uses cumulative positive acknowledgments. Each TCP segment contains the `sequence number` of the next byte that the sender of the acknowledgment expects to receive from the remote host. In theory, the `acknowledgment number` is only valid if the `ACK` flag of the TCP header is set. In practice, almost all [#fackflag]_ TCP segments have their `ACK` flag set.
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../../protocols/tls.rst:406
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reduce the latency of TLS
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../../glossary.rst:306
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For DNS servers and resolvers, an inverse query is a query for the domain name that corresponds to a given IP address.
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../../principles/network.rst:346
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sending a control packet back to the source if a router detects that a packet is looping inside the network
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../../principles/reliability.rst:261
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**1** **2** **3** **DLE** **STX** **4**
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../../principles/transport.rst:447
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To ensure a reliable delivery of the SDUs sent by each user over a connection, we need to consider the two streams that compose a connection as independent. A user should be able to release the stream that it uses to send SDUs once it has sent all the SDUs that it planned to send over this connection, but still continue to receive SDUs over the opposite stream. This `graceful` connection release is usually performed as shown in the figure below. One user issues a `Disconnect.request` primitive to its provider once it has issued all its `Data.request` primitives. The service provider will wait until all `Data.indication` primitives have been delivered to the receiving user before issuing the `Disconnnect.indication` primitive. This primitive informs the receiving user that it will no longer receive SDUs over this connection, but it is still able to issue `Data.request` primitives on the stream in the opposite direction. Once the user has issued all of its `Data.request` primitives, it issues a `Disconnnect.request` primitive to request the termination of the remaining stream. The service provider will process the request and deliver the corresponding `Disconnect.indication` to the other user once it has delivered all the pending `Data.indication` primitives. At this point, all data has been delivered, the two streams have been released successfully and the connection is completely closed.
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../../principles/sharing.rst:338
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[Abramson1970]_ analyzed the performance of ALOHANet under particular assumptions and found that ALOHANet worked well when the channel was lightly loaded. In this case, the frames are rarely retransmitted and the `channel traffic`, i.e. the total number of (correct and retransmitted) frames transmitted per unit of time is close to the `channel utilization`, i.e. the number of correctly transmitted frames per unit of time. Unfortunately, the analysis also reveals that the `channel utilization` reaches its maximum at :math:`\frac{1}{2 \times e}=0.186` times the channel bandwidth. At higher utilization, ALOHANet becomes unstable and the network collapses due to collided retransmissions.
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../../principles/security.rst:920
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When users want to communicate securely through a network, they need to exchange information such as the keys that will be used by an encryption algorithm even in the presence of an eavesdropper. The most widely used algorithm that allows two users to safely exchange an integer in the presence of an eavesdropper is the one proposed by Diffie and Hellman [DH1976]_. It operates with (large) integers. Two of them are public, the modulus, p, which is prime and the base, g, which must be a primitive root of p. The communicating users select a random integer, :math:`a` for Alice and :math:`b` for Bob. The exchange starts as :
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../../exercises/ipv6.rst:734
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The ``nodes`` command lists the routers and hosts that have been created in the mininet topology.
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../../exercises/routing-protocols.rst:1158
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What are the BGP messages that will be exchanged when the link between ``AS3`` and ``AS4`` fails ? How does this affect the reachability of the different hosts ?
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../../protocols/bgp.rst:313
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When comparing routes towards the same destination prefix, a BGP router always prefers the routes with the highest `local-pref`. If the BGP router knows several routes with the same `local-pref`, it prefers among the routes having this `local-pref` the ones with the shortest AS-Path.
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../../protocols/email.rst:240 • ../../protocols/email.rst:242
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4
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../../protocols/ethernet.rst:353
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Bandwidth
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../../protocols/http.rst:444
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An example of a non-retrievable URI is `urn:isbn:0-380-81593-1` which is an unique identifier for a book, through the urn scheme (see :rfc:`3187`). Of course, any URI can be made retrievable via a dedicated server or a new protocol but this one has no explicit protocol. Same thing for the scheme tag (see :rfc:`4151`), often used in Web syndication (see :rfc:`4287` about the Atom syndication format). Even when the scheme is retrievable (for instance with `http`), it is often used only as an identifier, not as a way to get a resource. See http://norman.walsh.name/2006/07/25/namesAndAddresses for a good explanation.
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../../protocols/ipv6.rst:323
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The IPv6 packet format was heavily inspired by the packet format proposed for the SIPP protocol in :rfc:`1710`. The standard IPv6 header defined in :rfc:`2460` occupies 40 bytes and contains 8 different fields, as shown in the figure below.
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../../protocols/ethernet.rst:305
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The `MAC address learning` algorithm allows switches to be plug-and-play. Unfortunately, the loops that arise when the network topology is not a tree are a severe problem. Forcing the switches to only be used in tree-shaped networks as hubs would be a severe limitation. To solve this problem, the inventors of Ethernet switches have developed the `Spanning Tree Protocol`. This protocol allows switches to automatically disable ports on Ethernet switches to ensure that the network does not contain any cycle that could cause frames to loop forever.
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../../protocols/tcp.rst:251
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`window`. a TCP receiver uses this 16 bits field to indicate the current size of its receive window expressed in bytes.
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