Exit Zen
72
../../protocols/tls.rst:385
English
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.
0/6260 · 626
73
../../principles/network.rst:332
English
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.
0/3190 · 319
73
../../principles/reliability.rst:249
English
`LF` : `0001010` b
0/180 · 18
73
../../principles/transport.rst:241
English
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.
0/10210 · 1021
73
../../principles/security.rst:860
English
A possible protocol could then be the following. Alice sends :math:`Cert(Alice_{pub},Ted)`. Bob replies with a random nonce.
0/1240 · 124
73
../../exercises/ipv6.rst:675
English
We can now create the hosts and the routers
0/430 · 43
73
../../exercises/routing-protocols.rst:1016
English
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
0/2280 · 228
73
../../protocols/bgp.rst:293
English
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 :
0/1830 · 183
73
../../protocols/email.rst:238 • ../../protocols/email.rst:240
English
3
0/100 · 1
73
../../protocols/ethernet.rst:331
English
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 :
0/4020 · 402
73
../../protocols/http.rst:385
English
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.
0/4970 · 497
73
../../protocols/ipv6.rst:261
English
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.
0/2450 · 245
73
../../protocols/ethernet.rst:261
English
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.
0/12370 · 1237
73
../../protocols/tcp.rst:235
English
The handling of the TCP options by TCP implementations is one of the many applications of the `robustness principle` which is usually attributed to `Jon Postel`_ and is often quoted as `"Be liberal in what you accept, and conservative in what you send"` :rfc:`1122`.
0/2660 · 266
73
../../protocols/tls.rst:392
English
Another interesting fact is are the key exchange schemes. In 2012, RSA was the dominant solution, used by more than 80% of the observed connections [KRA2018]_. In 2013, Edward Snowden revealed the surveillance activities of several governments. These revelations had a huge impact on the Internet community. The IETF, which standardizes Internet protocols, considered in :rfc:`7258` that such pervasive monitoring was an attack. Since then, several IETF working groups have developed solutions to counter pervasive monitoring. One of these solutions is to encourage `Perfect Forward Security`. Within TLS, this implies replacing RSA by an authenticated Diffie Hellman key exchange such as ECDHE. Measurements indicate that since summer 2014, ECDHE is more popular than RSA. In 2018, more than 90% of the observed TLS connections used ECDHE.
0/8400 · 840
74
../../glossary.rst:261
English
The Internet Message Access Protocol (IMAP), defined in :rfc:`3501`, is an application-level protocol that allows a client to access and manipulate the emails stored on a server. With IMAP, the email messages remain on the server and are not downloaded on the client.
0/2670 · 267
74
../../principles/network.rst:335
English
These three solutions have advantages and drawbacks. With the first solution, routers remain simple and do not need to perform any fragmentation operation. This is important when routers are implemented mainly in hardware. However, hosts must be complex since they need to store the packets that they produce if they need to pass through a link that does not support large packets. This increases the buffering required on the hosts.
0/4330 · 433
74
../../principles/reliability.rst:250
English
`DLE`: `0010000` b
0/180 · 18
74
../../principles/transport.rst:262
English
The example above shows a successful connection establishment. However, in practice not all connections are successfully established. One reason is that the destination user may not agree, for policy or performance reasons, to establish a connection with the initiating user at this time. In this case, the destination user responds to the `Connect.indication` primitive by a `Disconnect.request` primitive that contains a parameter to indicate why the connection has been refused. The service provider will then deliver a `Disconnect.indication` primitive to inform the initiating user.
0/5870 · 587
74
../../principles/sharing.rst:303
English
TDM as shown above can be completely static, i.e. the same conversations always share the link, or dynamic. In the latter case, the two endpoints of the link must exchange messages specifying which conversation uses which byte inside each slot. Thanks to these control messages, it is possible to dynamically add and remove voice conversations from a given link.
0/3620 · 362