The Pointer

Name Starts at Offset

The question name bytes appear once, starting at a fixed DNS message offset.

highlighted = computed this step

The full name appears once

The question section stores the name bytes starting at message offset 12.

QNAME offset=12\text{QNAME offset}=12
Question name bytesThe question name starts at byte offset twelve in the DNS message.QNAME at offset 12136 bits / 17 bytes0x03777777076578616d706c6503636f6d00byte 0byte 1byte 2byte 300000011011101110111011101110111byte 4byte 5byte 6byte 700000111011001010111100001100001byte 8byte 9byte 10byte 1101101101011100000110110001100101byte 12byte 13byte 14byte 1500000011011000110110111101101101byte 1600000000len-www3www0x777777len-example7(cont.)example0x6578616d706c65len-com3com0x636f6dterminator0x00Parsed name - 17 byte QNAME.comexamplewww

Labels are length-prefixed

The bytes decode to www, example, and com using length bytes 3, 7, and 3.

3,7,33,7,3
Question name bytesThe question name starts at byte offset twelve in the DNS message.QNAME at offset 12136 bits / 17 bytes0x03777777076578616d706c6503636f6d00byte 0byte 1byte 2byte 300000011011101110111011101110111byte 4byte 5byte 6byte 700000111011001010111100001100001byte 8byte 9byte 10byte 1101101101011100000110110001100101byte 12byte 13byte 14byte 1500000011011000110110111101101101byte 1600000000len-www3www0x777777len-example7(cont.)example0x6578616d706c65len-com3com0x636f6dterminator0x00Parsed name - 17 byte QNAME.comexamplewww

The parsed tree is the same name

The tree is recomputed from the same QNAME bytes, not typed separately.

name labels=3\text{name labels}=3
Question name bytesThe question name starts at byte offset twelve in the DNS message.QNAME at offset 12136 bits / 17 bytes0x03777777076578616d706c6503636f6d00byte 0byte 1byte 2byte 300000011011101110111011101110111byte 4byte 5byte 6byte 700000111011001010111100001100001byte 8byte 9byte 10byte 1101101101011100000110110001100101byte 12byte 13byte 14byte 1500000011011000110110111101101101byte 1600000000len-www3www0x777777len-example7(cont.)example0x6578616d706c65len-com3com0x636f6dterminator0x00Parsed name - 17 byte QNAME.comexamplewww

Summary

The answer can point back to this earlier name instead of spelling it again.

saved name starts at=12\text{saved name starts at}=12
Question name bytesThe question name starts at byte offset twelve in the DNS message.QNAME at offset 12136 bits / 17 bytes0x03777777076578616d706c6503636f6d00byte 0byte 1byte 2byte 300000011011101110111011101110111byte 4byte 5byte 6byte 700000111011001010111100001100001byte 8byte 9byte 10byte 1101101101011100000110110001100101byte 12byte 13byte 14byte 1500000011011000110110111101101101byte 1600000000len-www3www0x777777len-example7(cont.)example0x6578616d706c65len-com3com0x636f6dterminator0x00Parsed name - 17 byte QNAME.comexamplewww