Ethernet LAN Switching Flashcards
define a LAN
network contained in relatively small area
Routers connect Lans.
Yes.
Do switches separate lans
no. router and or router interfaces do.
what makes up a ethernet frame?
header, packet, trailer.
what 5 fields are in the ethernet header
- preamble used for synchronization
- SFD(start frame delimiter) both 1,2 used for synchronization. To allow device to be prepared to receive rest of data in frame.
- Destination - layer 2 address to which frame is being source
- Source layer 2 address on the device which sent frame.
- Type - indicates layer 3 protocol. Usually IPv4 or 6. Sometimes its a lenth.
what field is in the trailer?
Only one. The FCS. Frame check Sequence. Used by receiving device to check for errors.
Preamble
Length, 8 bytes. (56 bits)
10101010 * 7
The purpose is to allow devices to synchronize their receiver clocks. To make sure they are ready to receive the rest of the frame and the data inside.
SFD (Start Frame Delimiter)
Length: 1 byte (8 bits)
Bit pattern is 10101011. Last bit is a one
Indicates end of preamble and beginning of the rest of frame.
Destination and source
Length: both are 6 bytes, 48 bits hexadecimal
MAC addresses
Indicating the devices sending and receiving the frame.
Consisting of dest. and source mac addresses
type/length field.
Can represent either the type or length of encapsulated packet.
2 bytes in length.
Can be represented by bytes
Value of 1500 or less indicates the LENGTH of the encapsulated packet.
Value of 1536 or more indicates the TYPE(usually IPv4 or 6.)
how is IPv4 and 6 represented in the Type filed
IPv4 = 0x0800 hex
2048
IPv6 = 0x86DD hex
34252
Frame Check Sequence
4 bytes
Is a Cyclic Redundancy Check.
Detects corrupted data by running CRC algorithm over the received data.
CRC
Cyclic Redundancy Check.
Used in FCS.
how big is data?
variable 46-1500 bytes
what do the first half of the 24 bit MAC address mean?
OUI (Organizationally Unique Identifier) Identify the manufacturer of the ethernet port.
