1.1 OSI And Encapsulation

Question 1

Layer 1

Answer 1

Physical
-this layer not about protocols
-signaling, cabling, connectors
(Cable, NIC, Hub)

-loopback tests, swap adapters, replace cables

Question 2

OSI

Answer 2

Open Systems Interconnection reference

-not a protocol suite
-more of a guide
-each layer has unique protocols

Question 3

Layer 2

Answer 3

Data Link

-basic network “language”
-data link control (DLC) protocols
-MAC on on Ethernet
- switching layer

-Ethernet,

Question 4

Ethernet header

Answer 4

Preamble - 7 bytes
Start of frame delimiter - 1 byte
Dest. MAC - 6 bytes
Source MAC - 6 bytes
Type - 2 bytes
Data - 42 to 1500 bytes
CRC - 4 bytes
Inter-frame gap - 12 bytes

Question 5

IP header

Answer 5

V4
Version | ihl | type of service | tot Len
Identification | flags | fragment offset
TTL | protocol | header checksum
Source address
Destination address
Options | padding

Question 6

TCP header

Answer 6

Source port | destination port
Sequence number
Acknowledgment number
Data offset | res | flags | window size
Header&data checksum|urgent ptr
Options

Question 7

UDP datagram header

Answer 7

Source port | Destination port
Length | header and data checksum

Question 8

MTU

Answer 8

Maximum Transmission Unit

-max packet size where it doesn’t fragment
-usually configured once
-can use ping to find the right size
-ping -f -l 1472 8.8.8.8
-fragments are always in multiples of 8 because of the # of fragmentation offset bits in the IP header.