add ethernet lan part 2

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+---
+id: 1772845705-JEBL
+aliases:
+  - Ethernet LAN Switching
+tags: []
+---
+
+# Ethernet LAN Switching (part 1)
+
+## [[OSI model]] - physical layer
+
+- Defines physical characteristics of the medium used to transfer data between devices
+- For example, [[voltage]]  levels, maximum transmission distances, physical connectors, cable specifications, etc..
+- Digital [[bits]] converted into electrical (for wired connections) or radio (for wireless connections) signals
+- All of the information in day 2 [[02. Interfaces and Cables]] (cables, pin layout, etc.) is related to the Physical layer.
+
+## OSI model - Data Link Layer
+
+- Provides node-to-node connectivity and data transfer (for example, PC to switch, switch to router, router to router)
+- Defines how data is formatted for transmission over a physical medium (for example, copper UTP cables)
+- Detects and (possibly) corrects Physical Layer errors.
+- Uses Layer 2 addressing separate from Layer 3 addressing
+- Switches operate at Layer 2.
+
+##  OSI Models - PDUs
+
+Layer 4 header - Data 
+Layer 3 header - Segment
+Layer 2 header - Packet
+Layer 1 header - Frame
+
+Protocol Data Units | PDUs
+
+## Ethernet Frame
+
+ethernet header | Packet | Ethernet Trailer
+
+### Ehternet Header
+
+Preamble | Start Frame Delimiter (SFD) | Destination | Source | Type or Length
+ 7 bytes           1 byte                  6 byte      6 byte     2 bytes
+
+#### Preamble
+
+- Length : 7 Bytes (56 bits)
+- Alternating 1's and 0's
+- 10101010 * 7
+- Allows devices to synchronize their receiver clocks
+
+#### SFD
+
+- Start Frame Delimiter
+- Length: 1 byte (8 bits)
+- 10101011
+- Marks the end of the preamble, and the beginning of the rest of the frame
+
+#### Destination & Source
+
+Indicate the devices sending and receiving the frame
+- Consist of the desination and source [[MAC Address]]
+- MAC = Media Access Constol
+- = 6 byte (48-bit) address of the physical device
+
+#### Type / Length
+
+- 2 byte (16-bit) field
+- A value of 1500 or less in this field indicate the LENGTH of the encapsulated  packet (in bytes)
+- A value of 1536 or greater in this field indicates the TYPE of the encapsulated packet (Usually [[IPv4]] or [[IPv6]])
+and the length is determined via other methods
+
+IPv4 = 0x0800 ([[hexadecimal]])
+(2048 in decimal)
+IPv6 = 0x86DD (hexadecimal)
+(34525 in decimal)
+
+### Ethernet Trailer
+
+Frame Check Sequence (FCS)
+        4 bytes
+
+#### Frame Check Sequence
+
+- 4 bytes (32 bits) in length
+- Detects corrupted data by running a 'CRC' algorithm over the received data
+- CRC = Cycling Redundancy Check
+
+## Mac Address
+
+- 6-byte (48-bit) physical address assigned to the device when it is made
+- AKA ' Burned-in Address' (BIA)
+- Is globally unique
+- The first 3 bytes are the OUI (Organizationally Unique Identifier), which is assigned to the company making the device
+- The last 3 bytes are unique to the device itself
+- Written as 12 hexadecimal character
+
+Unicast frame: a frame destined for a single target
+
+### Dynamically learned Mac Address
+
+Is a mac address learned by the switche automatically by looking at the frame Destination Frame
+
+if the Mac address is not in the switch mac address table it will flood the frame (send the frame at all the interfaces except the source mac address)
+until the PC replied to another pc
+**Unknown Unicast Frame** -> *Flood*
+
+if the Mac address is knowned by the switch it will directly send it in the interface
+**Known Unicast Frame** -> *Forward*
+
+*Dynamically Mac Addresses are removed from the MAC address table after 5 minutes of inactivity*
+
+