Originator's address in a packet header
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. What does the originator's address in a packet header identify?
2. Which statement is correct?
3. A packet arrives with a missing or damaged packet. How can the receiver use the originator's address?
4. Laptop A sends a packet to Server B. Which IP address is the originator's address?
5. Server B wants to reply to a packet from Laptop A. Which address does it use as the destination of its reply?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1originator address: 192.168.1.20 | Asend_reply_to(header.originator) | |
| 2destination address: 203.0.113.9 | BThe IP address of the device that sent the packet, stored in the header | |
| 3The receiver uses the originator's address to reply or to ask for a lost packet to be sent again | CThe originator's address is the address of the device that sent the packet, not the device that receives it. | |
| 4A header holds two different addresses: the sender's (originator) and the receiver's (destination) | DThe IP address of the device the packet is being sent to, which is different from the originator's address | |
| 5reply_to(header.destination) | Eheader = [originator, destination] | |
| 6originator = address of the receiving device | FThe reply is sent to the destination address, which is the receiver's own address. A reply must go to the originator's address. |
C
Definitions
originator's address
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
// Device 10.0.0.5 sends the packet
header.destination ← 10.0.0.9
header.__________ ← 10.0.0.5
2.
// Reply to the device that sent the packet
SEND reply TO header.__________
3.
// Packet 4 is missing, ask for a resend
resendTo ← header.__________
4.
// Reply goes back to the sender
reply.destination ← ______.originator
5.
// 10.0.0.9 is the receiving device
header.originator ← 10.0.0.5
header.___________ ← 10.0.0.9
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
packet.origin ← 192.168.1.5
B
packet.dest ← 10.0.0.8
C
reply.dest ← packet.dest
Question 2
A
header.origin ← receiver_ip
B
header.dest ← receiver_ip
C
SEND(packet)
Question 3
A
sender ← packet.dest
B
OUTPUT 'Packet from ', sender
C
reply.dest ← sender
Question 4
A
IF packet.corrupt = TRUE THEN
B
request.dest ← packet.number
C
SEND(request)
D
ENDIF
Question 5
A
my_ip ← 192.168.1.5
B
packet.origin ← 10.0.0.8
C
packet.dest ← 10.0.0.8
D
SEND(packet)
Answer Key
Originator's address in a packet header
Section A: Quick Questions
Q1
B — The device that sent the packet
Q2
A — The originator's address tells the receiver who sent the packet
Q3
B — To ask the sender to resend the packet
Q4
A — The IP address of Laptop A
Q5
A — The originator's address from the received packet
Section B: Match the Pairs
Q1
originator address: 192.168.1.20 → The IP address of the device that sent the packet, stored in the header
Q2
destination address: 203.0.113.9 → The IP address of the device the packet is being sent to, which is different from the originator's address
Q3
The receiver uses the originator's address to reply or to ask for a lost packet to be sent again → send_reply_to(header.originator)
Q4
A header holds two different addresses: the sender's (originator) and the receiver's (destination) → header = [originator, destination]
Q5
reply_to(header.destination) → The reply is sent to the destination address, which is the receiver's own address. A reply must go to the originator's address.
Q6
originator = address of the receiving device → The originator's address is the address of the device that sent the packet, not the device that receives it.
Section C: Definitions
Q1
originator's address — The IP address of the device that sent the packet, held in the header so the receiver knows who sent it and can reply or ask for a resend. It differs from the destination address.Section D: Fill in the Blanks
Q1
// Device 10.0.0.5 sends the packet
header.destination ← 10.0.0.9
header.originator ← 10.0.0.5Q2
// Reply to the device that sent the packet
SEND reply TO header.originatorQ3
// Packet 4 is missing, ask for a resend
resendTo ← header.originatorQ4
// Reply goes back to the sender
reply.destination ← header.originatorQ5
// 10.0.0.9 is the receiving device
header.originator ← 10.0.0.5
header.destination ← 10.0.0.9Section E: Spot the Error
Q1
C — A reply must go back to the device that sent the packet, so it uses the originator's address: reply.dest ← packet.origin. Using the destination address would send the reply to the receiver itself.
Q2
A — The originator's address is the address of the device that sends the packet, so it should be header.origin ← sender_ip. The receiver's address belongs in the destination field.
Q3
A — The sender is found from the originator's address in the header: sender ← packet.origin. The destination address only tells you where the packet is going.
Q4
B — A resend request must be addressed to the device that sent the packet, so it needs the originator's address: request.dest ← packet.origin. The packet number is not an address.
Q5
B — The originator's address is the sender's own IP address, so it should be packet.origin ← my_ip. 10.0.0.8 is the destination address, which has its own field.