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73 ../../protocols/ethernet.rst:261
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 1237/10000 · 1237
73 ../../protocols/tcp.rst:235
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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`. 266/10000 · 266
73 ../../protocols/tls.rst:392
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — 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. 840/10000 · 840
73 ../../bibliography.rst:96
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Hogg, S. Vyncke, E., `IPv6 Security <http://www.ciscopress.com/store/ipv6-security-9780133346312>`_, Cisco Press, 2008 118/10000 · 118
74 ../../glossary.rst:69
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — internet 8/10000 · 8
74 ../../principles/network.rst:425
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Furthermore, a single large packet may potentially need to be retransmitted several times. Consider for example a network similar to the one shown above but with four routers. Assume that the link `R1->R2` supports 1000 bytes packets, link `R2->R3` 800 bytes packets and link `R3->R4` 600 bytes packets. A host attached to `R1` that sends large packet will have to first try 1000 bytes, then 800 bytes and finally 600 bytes. Fortunately, this scenario does not occur very often in practice and this is the reason why this solution is used in real networks. 556/10000 · 556
74 ../../principles/reliability.rst:259
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — `LF` : `0001010` b 18/10000 · 18
74 ../../principles/sharing.rst:478
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Amateur packet radio 20/10000 · 20
74 ../../principles/transport.rst:309
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A second reason is when the service provider is unable to reach the destination user. This might happen because the destination user is not currently attached to the network or due to congestion. In these cases, the service provider responds to the `Connect.request` with a `Disconnect.indication` primitive whose `reason` parameter contains additional information about the failure of the connection. 401/10000 · 401
74 ../../principles/security.rst:885
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Until now, we have only discussed the authentication problem. This is an important but not sufficient step to have a secure communication between two users through an insecure network. To securely exchange information, Alice and Bob need to both : 247/10000 · 247
74 ../../exercises/ipv6.rst:682
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — With this ``build`` method, we can now launch the network by using the python code below. 89/10000 · 89
74 ../../exercises/routing-protocols.rst:1029
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Another interesting utilization IPMininet_ is to explore the impact of a link failure. We start from a small variant of the above topology. 139/10000 · 139
74 ../../protocols/bgp.rst:295
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — the router has been manually configured by the network operator to always advertise one or several routes on a BGP session. For example, on the BGP session between UCLouvain and its provider, belnet_ , UCLouvain's router always advertises the `2001:6a8:3080/48` IPv6 prefix assigned to the campus network 304/10000 · 304
74 ../../protocols/email.rst:238
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — D 1/10000 · 1
74 ../../protocols/ethernet.rst:334
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — the `identifier` of the root switch (`R`) 41/10000 · 41
74 ../../protocols/http.rst:387
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A first solution is to force the users to be authenticated. This was the solution used by `FTP` to control the files that each user could access. Initially, user names and passwords could be included inside URIs :rfc:`1738`. However, placing passwords in the clear in a potentially publicly visible URI is completely insecure and this usage has now been deprecated :rfc:`3986`. HTTP supports several extension headers :rfc:`2617` that can be used by a server to request the authentication of the client by providing his/her credentials. However, user names and passwords have not been popular on web servers as they force human users to remember one user name and one password per server. Remembering a password is acceptable when a user needs to access protected content, but users will not accept to remember a unique user name and password for each web sites that they visit. 878/10000 · 878
74 ../../protocols/ipv6.rst:265
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The addresses described above are unicast addresses. These addresses are used to identify (interfaces on) hosts and routers. They can appear as source and destination addresses in the IPv6 packets. When a host sends a packet towards a unicast address, this packet is delivered by the network to its final destination. There are situations, such as when delivering video or television signal to a large number of receivers, where it is useful to have a network that can efficiently deliver the same packet to a large number of receivers. This is the `multicast` service. A multicast service can be provided in a LAN. In this case, a multicast address identifies a set of receivers and each frame sent towards this address is delivered to all receivers in the group. Multicast can also be used in a network containing routers and hosts. In this case, a multicast address identifies also a group of receivers and the network delivers efficiently each multicast packet to all members of the group. Consider for example the network below. 1033/10000 · 1033
74 ../../protocols/ethernet.rst:263
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The pseudo-code below details how an Ethernet switch forwards Ethernet frames. It first updates its `MAC address table` with the source address of the frame. The `MAC address table` used by some switches also contains a timestamp that is updated each time a frame is received from each known source address. This timestamp is used to remove from the `MAC address table` entries that have not been active during the last `n` minutes. This limits the growth of the `MAC address table`, but also allows hosts to move from one port to another. The switch uses its `MAC address table` to forward the received unicast frame. If there is an entry for the frame's destination address in the `MAC address table`, the frame is forwarded selectively on the port listed in this entry. Otherwise, the switch does not know how to reach the destination address and it must forward the frame on all its ports except the port from which the frame has been received. This ensures that the frame will reach its destination, at the expense of some unnecessary transmissions. These unnecessary transmissions will only last until the destination has sent its first frame. Multicast and Broadcast frames are also forwarded in a similar way. 1217/10000 · 1217
74 ../../protocols/tcp.rst:237
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Concerning the TCP options, the robustness principle implies that a TCP implementation should be able to accept TCP options that it does not understand, in particular in received `SYN` segments, and that it should be able to parse any received segment without crashing, even if the segment contains an unknown TCP option. Furthermore, a server should not send in the `SYN+ACK` segment or later, options that have not been proposed by the client in the `SYN` segment. 466/10000 · 466
74 ../../protocols/tls.rst:395
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The last point is the difficulty of deploying TLS servers [KMS2017]_. When TLS servers are installed, the system administrator needs to obtain certificates and configure a range of servers. Initially, getting certificates was complex and costly, but initiatives such as https://letsencrypt.org have simplified this workflow. 324/10000 · 324