The request already knows the target IP address, but the target MAC field is blank.
A zero field marks the missing answer
In the request, the target IP is known but the target MAC is not. That missing MAC is carried as all zero bytes.
target MAC = 0 x 000000000000 \text{target MAC}=0x000000000000 target MAC = 0 x 000000000000 Request target MAC The request carries a zero target MAC because that is the missing value. Request target MAC 224 bits / 28 bytes 0x0001080006040001001122334455c0a8010a000000000000c0a80101 byte 0 byte 1 byte 2 byte 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 byte 4 byte 5 byte 6 byte 7 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 byte 8 byte 9 byte 10 byte 11 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 1 0 0 1 1 byte 12 byte 13 byte 14 byte 15 0 1 0 0 0 1 0 0 0 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 byte 16 byte 17 byte 18 byte 19 0 0 0 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 20 byte 21 byte 22 byte 23 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 24 byte 25 byte 26 byte 27 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 htype 1 ptype 0x0800 hlen 6 plen 4 opcode 1 sender-mac 0x001122334455 (cont.) sender-ip 192.168.1.10 (cont.) (cont.) target-mac 0x000000000000 target-ip 192.168.1.1
The IP is the known clue
The known target IP is 192.168.1.1. The request asks which local MAC owns that address.
target IP = 192.168.1.1 \text{target IP}=192.168.1.1 target IP = 192.168.1.1 Request target MAC The request carries a zero target MAC because that is the missing value. Request target MAC 224 bits / 28 bytes 0x0001080006040001001122334455c0a8010a000000000000c0a80101 byte 0 byte 1 byte 2 byte 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 byte 4 byte 5 byte 6 byte 7 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 byte 8 byte 9 byte 10 byte 11 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 1 0 0 1 1 byte 12 byte 13 byte 14 byte 15 0 1 0 0 0 1 0 0 0 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 byte 16 byte 17 byte 18 byte 19 0 0 0 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 20 byte 21 byte 22 byte 23 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 24 byte 25 byte 26 byte 27 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 htype 1 ptype 0x0800 hlen 6 plen 4 opcode 1 sender-mac 0x001122334455 (cont.) sender-ip 192.168.1.10 (cont.) (cont.) target-mac 0x000000000000 target-ip 192.168.1.1
The MAC is blank
The target MAC field is 0x000000000000. That exact zero value is the blank slot in the question.
blank MAC = 0 x 000000000000 \text{blank MAC}=0x000000000000 blank MAC = 0 x 000000000000 Request target MAC The request carries a zero target MAC because that is the missing value. Request target MAC 224 bits / 28 bytes 0x0001080006040001001122334455c0a8010a000000000000c0a80101 byte 0 byte 1 byte 2 byte 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 byte 4 byte 5 byte 6 byte 7 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 byte 8 byte 9 byte 10 byte 11 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 1 0 0 1 1 byte 12 byte 13 byte 14 byte 15 0 1 0 0 0 1 0 0 0 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 byte 16 byte 17 byte 18 byte 19 0 0 0 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 20 byte 21 byte 22 byte 23 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 24 byte 25 byte 26 byte 27 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 htype 1 ptype 0x0800 hlen 6 plen 4 opcode 1 sender-mac 0x001122334455 (cont.) sender-ip 192.168.1.10 (cont.) (cont.) target-mac 0x000000000000 target-ip 192.168.1.1
Summary
ARP request bytes can carry a known IP address beside a zero MAC address. The zero field is checked from the request bytes, not trusted from the lesson text.
opcode request = 1 \text{opcode request}=1 opcode request = 1 Request target MAC The request carries a zero target MAC because that is the missing value. Request target MAC 224 bits / 28 bytes 0x0001080006040001001122334455c0a8010a000000000000c0a80101 byte 0 byte 1 byte 2 byte 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 byte 4 byte 5 byte 6 byte 7 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 byte 8 byte 9 byte 10 byte 11 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 1 0 0 1 1 byte 12 byte 13 byte 14 byte 15 0 1 0 0 0 1 0 0 0 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 byte 16 byte 17 byte 18 byte 19 0 0 0 0 0 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 20 byte 21 byte 22 byte 23 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 byte 24 byte 25 byte 26 byte 27 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 htype 1 ptype 0x0800 hlen 6 plen 4 opcode 1 sender-mac 0x001122334455 (cont.) sender-ip 192.168.1.10 (cont.) (cont.) target-mac 0x000000000000 target-ip 192.168.1.1