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A switch network (in English, switch ) is equipment which connects several segments (cables) in a Data-processing network. It is generally about a case having several (between 4 and 100) ports Ethernet. It thus has same appearance as a Concentrateur ( hub ).

Contrary to a concentrator, a switch is not satisfied to reproduce on all the ports each screen which it receives. It can determine on which port it must send a screen, according to the MAC address for which the latter is intended. The switches are often used to replace concentrators.

Contrary to a Router, a switch (or a concentrator) does not deal with protocol IP. It uses the MAC addresses and not IP addresses to direct the data. The switches form networks of level 2 (Ethernet). These networks are connected between them by routers to form networks of level 3 (IP).

Operation

The switch draws up and updates a table of addresses MAC, which indicates to him on which port to direct the screens intended for a given address. When it receives a screen intended for an address present in this table, the switch returns the screen on the corresponding port. If the wearing of destination is the same one as that of the transmitter, the screen is not transmitted. If the address of the recipient is unknown, then it is an address of broadcast or a multicast, i.e. that it is necessary to send the screen to all the machines of the network. The switch sends simply the screen on all its ports except for the port of the transmitter.

When a screen enters the switch, this one preserves the MAC address of the transmitter and the port on which it received it in the table of address. Thus the table is drawn up and updated.

A switch is similar to a concentrator in the direction where it provides only one Domaine of diffusion. On the other hand, each port has its clean Domaine of collision. The switch uses the microphone-segmentation to divide the fields of collision, one by connected segment. Thus, only the interfaces network directly connected by a point-to-point bond request the medium. If the switch to which it is connected supports the Full-duplex, the field of collision is entirely eliminated.

Methods of transmission

The transmission of the packages can take place various manners:

  • Cut through : the switch reads just the address of the material and transmits it such as it is. No detection of error is carried out with this method.

  • Mode differed ( blind and forward ): the switch puts out of plug, and generally, an operation of checksum realizes on each screen before sending it.
  • Fragment free: the packages passed to a fixed flow, allowing to carry out a detection of simplified error. It is a compromise between the preceding methods.
  • Adaptive switching : is an automatic mode. According to the noted errors, the switch uses one of the three modes.

Additional functions

A switch can in certain cases:
  • to deal with several virtual networks,
  • to use the Spanning tree protocol to avoid loops network, in particular in a redundant architecture,
  • to act as Router S, one speaks then about liquid level switch 3 or L3.

The switches have also functionalities which make it possible the administrator to supervise the traffic:

  • the port mirroring (miroirisation of port): the switch sends a copy of all the packages to inspection a connection network.
  • the Switch Monitoring (SMON or monitoring of switch): the switch is described by RFC 2613, protocol to control the operations like the miroirisation of port.

Security issues

Several methods allow espionner on another Ordinateur the network without the co-operation of the switch:

  • ARP spoofing : mislead the targeted computer of the user by using your own MAC address instead of that of the footbridge of network or by using the emission mode broadcast.
  • MAC flooding (flood of MAC addresses): overload the switch with several MAC addresses so that it falls into a mode failopen . This last behaves then like simple a Concentrateur and diffuses the screens at all the stations of the network. This problem was detected and corrected in the majority of the recent switches. For oldest, an update of the Firmware should make it possible to avoid this chaotic behavior.

Typology

A switch connects channels Ethernet, Token-ring, ATM, Frame-Relay or other types of segments networks to packages of layer 2 of OSI model. The following categories are distinguished:
  • switch Ethernet (LAN switch)
  • Router or liquid level switch 3
  • Switch X25
  • Switch FR
  • Switch ATM
  • Switch MPLS (LSR, Label Switch Router)
  • telephone Switch (self-switching, PABX, PBX)
  • Frontal (FEP, communication controller)
  • Fiber_Channel switch FC in environment SAN Storage_Area_Network

See too

Related articles

External bonds

  • What are forwarding modes and how C they work.
  • To transform Switchs into HUB Documentation on a weakness of the switchs which aims to make become aware and to propose protections.

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