15th September 2010, basic communications - Thies
Ethernet (OSI Layer 2)
- request to OSI Layer 2:
- access method to the medium (CSMA / CD)
- error detection (error detection) via buzzer in the frame-Trailer ( FCS)
- Identification of upper layer protocols "
a) by the Type field in the header (DIX or Ethernet II) or
b) by the LLC field (IEEE 802.2)
- optional for Ethernet: Physical Addressing using MAC addresses in the header (destination (target), source (source))
Ethernet
first Development of Digital, Intel and Xerox (DIX hence-Net) => Ethernet II
second DIX on request from IEEE (Institute of Electrical and Electronics Engineers) whether an international standard can be made of it.
third IEEE formed two working groups:
- IEEE 802.3 (Working Group on access to the media ")
- IEEE 802.2 (Working Group on Identification Upper Layer)
4th IEEE establishes the international standards
- IEEE 802.3 (see the "MAC = Media Access Control Protocol)
- IEEE 802.2 (see the" Protocol LLC = logiKal Link Control)
5th Since the support of almost any network controller, two standards for Ethernet. Namely, Ethernet II and IEEE 802.3 (with the protocol IEEE 802.2 LLC =)
DIX-Net was proprietary, so the Ethernet standard was "invented" (IEEE802.2; IEE802.3).
Proprietary (property) = not open source
The frame in Ethernet II
- The preamble identifies the beginning and the end of the frame for OSI layer 1, the bit stream
- The destination MAC may be a broadcast address: FF-FF
-FF-FF-FF-FF (all bits set to 1)
- or a Multicast address;
01-00-5E-00-00-00
to:
01-00-5E-7F-FF-FF
or course to a unicast address (addressed exactly a network participants)
- The source MAC is not a broadcast address!
- The Type field indicates the "upper-layer protocol" in this case IP (0x0800)
- the data field (data) contains the complete OSI-3 packet, called a datagram.
- FCS = Frame check sequence - This is a CRC checksum, then a hash value ( A hash function or Scatter value function is a function or mapping that to a command from a usually large source volume, the issue, hash code (or hash ) produced, usually from a smaller target set.) for the Frame calculated. Herewith the integrity of the frame is guaranteed. Transmission errors are avoided.
The frame in Ethernet 802.3
is referred to by the two sublayer at OSI 2:
- Top sublayer: 802.2 LLC (Logical Link Control)
Also referred to as OSI layer 2b. LLC (Logical Link Control) is responsible for the Steurung communication on OSI layer 2. Among others, LLC recognizes the OSI-3 protocols from the transmitter / receiver (upper layer protocol), manages the data connection and controls the flow control. For LLC, there are different types and services.
bottom sublayer: 802.3 MAC (Media Access Control)
Also referred to as OSI layer 2, media access control by using CSMA / CD (Carrier Sense Multiple Access / Collision Detection)
- The Präamber marks the beginning and the end of the frame for the OSI layer 1, the bit stream.
-The destination MAC may be a broadcast address: FF-FF
-FF-FF-FF-FF (all bits set to 1)
or a multicast address:
01-00 -5E-00-00-00
to
01-00-5E-7F-FF-FF
course or a unicast address (addressed to exactly one network node).
-The source MAC is not a broadcast address.
-The Length field is the length of the frame (data and FCS)
-The data field (data) contains the complete OSI-3 package, called a datagram.
-FCS = Frame check sequence - here is a CRC checksum, a hash value that is calculated for the frame. This ensures the integrity of the frames.
Important Ethernet specifications
! Exam! The best way to learn by heart.
| Name: | IEEE standard: | data rate: | Cable: |
| Ethernet | IEEE 802.3 | 10 BWhen / s | coax and TP |
| Fast Ethernet (FE) | IEEE 802.3u | 100 BWhen / s | TP and fiber |
| Gigabit Ethernet (GE) | IEEE 802.3ab / z | 1000 BWhen / s | TP and fiber |
| 10G Ethernet | IEEE 802.3ae | 10 000 BWhen / s | fiber |
that regard or the exact specifications that I transfer today but not directly. 've Even as Domunetation ... and, as already described, it is best to be the stuff to memorize.
MAC addresses
? - The MAC address is the hardware address of each network adapter that is used for unique Identifizirung each device on the network, the OSI layer 2 is called. ? ?
~ ~ Deutschh
- The MAC address is a 48-bit hexadecimal (base is 16)
The individual values are represented in hexadecimal as follows:
Windows: 05-00-0c-23-1a-ff
Linux / Unix: 05:00:0 c: 23:1 a: ff
Cisco: 0500.0c23c.1aff
- The first 24 bits (first half) form the "Organisational Unique Identifier, the manufacturer code. Cisco is often referred to as the OUI.
- The second half (last 24 bits), the manufacturer has the network card. This guarantees that the MAC addresses are unique worldwide.
- MAC addresses can be changed.
- In a LAN will use the MAC address to be addressing. Why should a MAC address will never be used twice.
- Even with the MAC addresses, there are different groups:
Broadcast: FF-FF-FF-FF-FF-FF (all bits set to 1) to all on the LAN.
Multicast 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF, a special group.
unicast: An exact (known) address.
-? Swichtes choose a forward path based on the MAC addresses that are assigned to the port through which the desired goal is reached.? Swichtes the logical way to choose a known MAC address ... - One probably. better?
MAC ("Clear" address) = Media Access Control
'Burned-in address' Read
first 6 digits = "producer"
arp-a arp-cache =
getmac ='s own mac address
unicast MAC address
- a world first assigned MAC address of a network interface
multicast MAC address (Flood)
- A specific group of participants (depending on service)
- Routing Protocols Using Multicast addresses
broadcast MAC address (Flood)
- address = "public address to ALL!
Unknown Unicast = Not known "network operator". (Flood)
network interface responds to unicast and broadcast addresses. It should of / on the software level to another mac address to the interface responds autherisierung on multicast addresses.
times in passing: "Embedded Small ="
And only a very short and sweet (I'm tired ...)
Switching Basics
- you work on OSI Layer 2
- share network segments into collision domains. (Simultaneous communication over multiple radially arranged buses)
- Bridges work at the MAC level or Logical Link level.
operation of bridges and switches:
A) learn
you are learning to which port the device. Save the MAC address (source MAC) in an internal table.
B) forwarding / filtering
Bridges and switches forward traffic to the more intelligent information in your table.
c) avoid Layer 2 loops in which they use the Spanning Tree Protocol (STP).
VLAN - Virtual Local Area Network
The documentation I transfer one probably even tomorrow. For now this must suffice, designed by myself on VLAN ... MÜÜDDDEEE!
It combines in a different VLAN ports of different switches to an additional virtual switch (a new logical local LAN).
My goodness ... quite a pile of wood!
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