IPv4 Header, IPv6, and TCP/UDP Header

Question 1

How many fields for the IPv4 Header

Answer 1

10 fields?

Question 2

What is the version field?

Answer 2

Version/IHL - identifies the field of IP used. IPv4 or IPv6.
0100
0110
- IHL is necessary to indicate the total length of the header. Identifies the length of the header in 4-byte increments

Question 3

List the fields?

Question 4

What is the DSCP Field

Answer 4

DSCP/ECN Field - priority of a packet. Used for QoS. (Streaming voice and video)

ECN Field - cool! Provides end-to-end notification of network congestion without dropping packets.

Question 5

Next Line - Line 2
What is the identification field?

Answer 5

If a packet is fragmented due to being too large, this field is used to identify which packet the fragment belongs to.
- All fragments of the same packet will have their own IPv4 header, with the same value in this field.

Question 6

What is the total length field

Answer 6

Indicates total length of the packet - L3 header plus layer 4 segment)
- minimum value of 20 bytes with no encapsulated data.

Question 7

What is the IHL Field?

Answer 7

This is meant to go in the beginning. IHL field has a minimum value of 5 (=20 bytes) and max value of 15 (15x4 =60 bytes).
- Remember, it identifies the header in 4 byte increments

Question 8

What is the fragment Offset Field

Answer 8

• Used to indicate the position of the fragment within the original, unfragmented IP packet.

Question 8

What is the Flags field?

Answer 8

Used to control/identify fragments
- Bit 0, always set to 0
- Bit 1: Don’t fragment (DF)
- Bit 2 - More fragments (MF), set to 1 if there are more fragments in the packet, set to 0 for the last fragment.

Question 9

New Line - Line 3
What is the Time-to-live field?

Answer 9

Used to prevent infinite loops. A route will drop a packet with a TTL of 0. Each time the packet arrives at the router, the router decreases the TTL by 1.

Question 10

What is the Header Checksum Field?

Answer 10

Checks for errors in the IPv4 packet.

Question 11

What is the protocol field?

Answer 11

Indicates the protocol of the encapsulated L4PDU. (TCP/UDP/ICMP/OSPF)

Question 12

What is the source IP field?

Answer 12

32 bit

Question 13

What is the Destination IP field?

Answer 13

32 bit

Question 14

What is the Options Field?

Answer 14

If the IHL is greater than 5, it means that options are present.

Question 15

New Section - TCP/UDP

Question 16

TCP Header

Answer 16

A bunch of fields

Question 17

What is the source Port

Answer 17

Specifies the port number of the sender

Question 18

What is the destination port

Answer 18

Specifies the port number of the receiver

Question 19

What is the sequence number field

Answer 19

Sequencing and reliable communication (3-way handshake),

Question 20

What is the ACK number field

Answer 20

Used by the receiver to request the next TCP segment.

Question 21

What is the DO field

Answer 21

Indicates length of the TCP header.

Question 22

What is the RSV field

Answer 22

Reserved field

Question 23

What are the flag fields?

Answer 23

URG - urgent pointer. When this bit is set, it should take priority over other data.
ACK - used for the ack
PSH - push function.
RST - resets the connection
SYN - we use this for an initial three way handshake and its used to set the initial sequence
FIN - finish bit is used to end the TCP connection. TCP is full duplex, both parties have to send a fin!

Question 24

What is the window

Answer 24

Specifies how many bytes the receiver is willing to receive. Receiver can tell the sender for example to send more data.

Question 25

What is the checksum

Answer 25

Check to see if the TCP header is ok or not.

Question 26

What is the urgent point

Answer 26

Used to indicate where the urgent data ends.