cnp3-ebook/protocols/ethernet — English @ Weblate

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42 ../../protocols/ethernet.rst:178

	English 1000Base-SX 11/10000 · 11
43 ../../protocols/ethernet.rst:178

	English Two multi-mode or single mode optical fibers with lasers 56/10000 · 56
44 ../../protocols/ethernet.rst:179 • ../../protocols/ethernet.rst:358

	English 10 Gbps 7/10000 · 7
45 ../../protocols/ethernet.rst:179

	English Optical fiber but also Category 6 UTP 37/10000 · 37
46 ../../protocols/ethernet.rst:180

	English 40-100 Gbps 11/10000 · 11
47 ../../protocols/ethernet.rst:180

	English Optical fiber (experiences are performed with copper) 53/10000 · 53
48 ../../protocols/ethernet.rst:192 • ../../protocols/ethernet.rst:308

	English Footnotes 9/10000 · 9
49 ../../protocols/ethernet.rst:193

	English Additional information about the history of the Ethernet technology may be found at http://ethernethistory.typepad.com/ 119/10000 · 119
50 ../../protocols/ethernet.rst:195

	English Initially, the OUIs were allocated by Xerox [DP1981]_. However, once Ethernet became an IEEE and later an ISO standard, the allocation of the OUIs moved to IEEE. The list of all OUI allocations may be found at http://standards.ieee.org/regauth/oui/index.shtml 259/10000 · 259
51 ../../protocols/ethernet.rst:197

	English The official list of all assigned Ethernet type values is available from http://standards.ieee.org/regauth/ethertype/eth.txt 124/10000 · 124
52 ../../protocols/ethernet.rst:199

	English The attentive reader may question the need for different `EtherTypes` for IPv4 and IPv6 while the IP header already contains a version field that can be used to distinguish between IPv4 and IPv6 packets. Theoretically, IPv4 and IPv6 could have used the same `EtherType`. Unfortunately, developers of the early IPv6 implementations found that some devices did not check the version field of the IPv4 packets that they received and parsed frames whose `EtherType` was set to `0x0800` as IPv4 packets. Sending IPv6 packets to such devices would have caused disruptions. To avoid this problem, the IETF decided to apply for a distinct `EtherType` value for IPv6. Such a choice is now mandated by :rfc:`6274` (section 3.1), although we can find a funny counter-example in :rfc:`6214`. 779/10000 · 779
53 ../../protocols/ethernet.rst:201

	English These network interfaces compute the TCP checksum while a segment is transferred from the host memory to the network interface [SH2004]_. 137/10000 · 137
54 ../../protocols/ethernet.rst:203

	English Fortunately, IEEE was able to define the [IEEE802.3]_ frame format while maintaining backward compatibility with the Ethernet [DIX]_ frame format. The trick was to only assign values above 1500 as `EtherType` values. When a host receives a frame, it can determine whether the frame's format by checking its `EtherType/Length` field. A value lower smaller than `1501` is clearly a length indicator and thus an [IEEE802.3]_ frame. A value larger than `1501` can only be type and thus a [DIX]_ frame. 497/10000 · 497
55 ../../protocols/ethernet.rst:207

	English Ethernet Switches 17/10000 · 17
56 ../../protocols/ethernet.rst:211

	English Increasing the physical layer bandwidth as in `Fast Ethernet` was only one of the solutions to improve the performance of Ethernet LANs. A second solution was to replace the hubs with more intelligent devices. As `Ethernet hubs` operate in the physical layer, they can only regenerate the electrical signal to extend the geographical reach of the network. From a performance perspective, it would be more interesting to have devices that operate in the datalink layer and can analyze the destination address of each frame and forward the frames selectively on the link that leads to the destination. Such devices are usually called `Ethernet switches` [#fbridges]_. An `Ethernet switch` is a relay that operates in the datalink layer as is illustrated in the figure below. 773/10000 · 773
57 ../../protocols/ethernet.rst:248

	English An `Ethernet switch` understands the format of the Ethernet frames and can selectively forward frames over each interface. For this, each `Ethernet switch` maintains a `MAC address table`. This table contains, for each MAC address known by the switch, the identifier of the switch's port over which a frame sent towards this address must be forwarded to reach its destination. This is illustrated below with the `MAC address table` of the bottom switch. When the switch receives a frame destined to address `B`, it forwards the frame on its South port. If it receives a frame destined to address `D`, it forwards it only on its North port. 639/10000 · 639
58 ../../protocols/ethernet.rst:255

	English Operation of Ethernet switches 30/10000 · 30
59 ../../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. 1237/10000 · 1237
60 ../../protocols/ethernet.rst:263

	English 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
61 ../../protocols/ethernet.rst:287

	English Security issues with Ethernet hubs and switches 47/10000 · 47

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