Exit Zen
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../../exercises/trace.rst:111
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the `wireshark wiki <https://wiki.wireshark.org/>` page on `Display filters <https://wiki.wireshark.org/DisplayFilters>`_
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../../protocols/bgp.rst:72
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Finally, the last type of peering relationship is the `sibling`. Such a relationship is used when two domains exchange all their routes in both directions. In practice, such a relationship is only used between domains that belong to the same company.
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../../protocols/congestion.rst:110
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The second difficulty is how to allow the receiver to inform the sender of the reception of network packets marked with the `CE` bit. In reliable transport protocols like TCP and SCTP, the acknowledgments can be used to provide this feedback. For TCP, two options were possible : change some bits in the TCP segment header or define a new TCP option to carry this information. The designers of ECN opted for reusing spare bits in the TCP header. More precisely, two TCP flags have been added in the TCP header to support ECN. The `ECN-Echo` (ECE) is set in the acknowledgments when the `CE` was set in packets received on the forward path.
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../../protocols/dnssec.rst:196
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The next step is to contact `ns.org`, the `NS` responsible for the `.org` TLD to retrieve the `NS` record for the `example.org` domain. This record is accompanied by a `RRSIG` record that authenticates it. This `RRSIG` record is signed with the key of the `.org` domain. Alice's resolver can retrieve this public key as the `DNSKEY` record for the `.org`, but how can it trust this key since it is distributed by using the DNS and could have been modified by attackers ? DNSSEC solves this problem by using the `DS` record that is stored in the parent zone (in this case, the root zone). This record contains a hash of a public key that is signed with a `RRSIG` signature. Since Alice's resolver's trusts the root key, it can validate the signature of the `DS` record for the `.org` domain. It can then retrieve the `DNSKEY` record for this domain from the DNS and compare the hash of this key with the `DS` record. If they match, the public key of the `.org` domain can be trusted. The same technique is used to obtain and validate the key of the `example.org` domain. Once this key is trusted, Alice's resolver can request the `AAAA` record for `www.example.org` and validate its signature.
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../../protocols/email.rst:109
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A simple email message containing the `From:`, `To:`, `Subject:` and `Date:` header lines and two lines of body is shown below.
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../../protocols/ethernet.rst:118
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The introduction of the twisted pairs led to two major changes to Ethernet. The first change concerns the physical topology of the network. 10Base2 and 10Base5 networks are shared buses, the coaxial cable typically passes through each room that contains a connected computer. A 10BaseT network is a star-shaped network. All the devices connected to the network are attached to a twisted pair cable that ends in the telecom closet. From a maintenance perspective, this is a major improvement. The cable is a weak point in 10Base2 and 10Base5 networks. Any physical damage on the cable broke the entire network and when such a failure occurred, the network administrator had to manually check the entire cable to detect where it was damaged. With 10BaseT, when one twisted pair is damaged, only the device connected to this twisted pair is affected and this does not affect the other devices. The second major change introduced by 10BaseT was that is was impossible to build a 10BaseT network by simply connecting all the twisted pairs together. All the twisted pairs must be connected to a relay that operates in the physical layer. This relay is called an `Ethernet hub`. A `hub` is thus a physical layer relay that receives an electrical signal on one of its interfaces, regenerates the signal and transmits it over all its other interfaces. Some `hubs` are also able to convert the electrical signal from one physical layer to another (e.g. 10BaseT to 10Base2 conversion).
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../../protocols/http.rst:100
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More complex HTML elements can also include optional attributes in the start tag ::
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../../protocols/http2.rst:146
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Let us first examine how HTTP/2.0 structures the bytestream of the underlying connection.
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../../protocols/ipv6.rst:100
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The IPng address size
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../../protocols/ethernet.rst:49
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The fourth part of the Ethernet frame is the payload. The minimum length of the payload is 46 bytes to ensure a minimum frame size, including the header of 512 bits. The Ethernet payload cannot be longer than 1500 bytes. This size was found reasonable when the first Ethernet specification was written. At that time, Xerox had been using its experimental 3 Mbps Ethernet that offered 554 bytes of payload and :rfc:`1122` required a minimum MTU of 572 bytes for IPv4. 1500 bytes was large enough to support these needs without forcing the network adapters to contain overly large memories. Furthermore, simulations and measurement studies performed in Ethernet networks revealed that CSMA/CD was able to achieve a very high utilization. This is illustrated in the figure below based on [SH1980]_, which shows the channel utilization achieved in Ethernet networks containing different numbers of hosts that are sending frames of different sizes.
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../../protocols/routing.rst:71
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Compared to the basics of link-state routing protocols that we discussed in section :ref:`linkstate`, there are some particularities of OSPF that are worth discussing. First, in a large network, flooding the information about all routers and links to thousands of routers or more may be costly as each router needs to store all the information about the entire network. A better approach would be to introduce hierarchical routing. Hierarchical routing divides the network into regions. All the routers inside a region have detailed information about the topology of the region but only learn aggregated information about the topology of the other regions and their interconnections. OSPF supports a restricted variant of hierarchical routing. In OSPF's terminology, a region is called an `area`.
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../../protocols/rpc.rst:94
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Compared with XDR, the main advantage of JSON is that the transfer syntax is easily readable by a human. However, this comes at the expense of a less compact encoding. Some data encoded in JSON will usually take more space than when it is encoded with XDR. More compact encoding schemes have been defined, see e.g. [BH2013]_ and the references therein.
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../../protocols/ssh.rst:193
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Single use keys
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../../protocols/tcp.rst:48
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the `SYN` flag is used during connection establishment
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../../protocols/tls.rst:47
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FTP
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../../protocols/transport-service.rst:60
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`0:0:0:0:0:0:0:1` is represented as `::1`
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../../protocols/udp.rst:71
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The checksum of the UDP segment is computed over :
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../../protocols/wifi.rst:24
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802.11b
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../../bibliography.rst:68
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Sally Floyd and Van Jacobson. 1993. `Random early detection gateways for congestion avoidance <https://dx.doi.org/10.1109/90.251892>`_. IEEE/ACM Transactions Networking 1, 4 (August 1993), 397-413.
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../../glossary.rst:235
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BNF
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