Addresses & Boundary

Source Address

The IPv6 source address is a wide fixed-header field.

highlighted = computed this step

The source address is wide

The source address field is 128 bits wide.

source bits=128\text{source bits}=128
Source addressThe source and destination addresses are decoded from the fixed header.Source address320 bits / 40 bytes0x600123450004114020010db800000000000000000000000120010db8000000000000000000000002byte 0byte 1byte 2byte 301100000000000010010001101000101byte 4byte 5byte 6byte 700000000000001000001000101000000byte 8byte 9byte 10byte 1100100000000000010000110110111000byte 12byte 13byte 14byte 1500000000000000000000000000000000byte 16byte 17byte 18byte 1900000000000000000000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000001byte 24byte 25byte 26byte 2700100000000000010000110110111000byte 28byte 29byte 30byte 3100000000000000000000000000000000byte 32byte 33byte 34byte 3500000000000000000000000000000000byte 36byte 37byte 38byte 3900000000000000000000000000000010version6traffic-class0flow-label0x12345payload-length4next-header17->UDPhop-limit64source2001:db8::1(cont.)(cont.)(cont.)destination2001:db8::2(cont.)(cont.)(cont.)

Source is pinned as exact bits

The rendered address comes from the exact integer 0x20010db8000000000000000000000001.

src=0x20010db8000000000000000000000001\text{src}=0x20010db8000000000000000000000001
Source addressThe source and destination addresses are decoded from the fixed header.Source address320 bits / 40 bytes0x600123450004114020010db800000000000000000000000120010db8000000000000000000000002byte 0byte 1byte 2byte 301100000000000010010001101000101byte 4byte 5byte 6byte 700000000000001000001000101000000byte 8byte 9byte 10byte 1100100000000000010000110110111000byte 12byte 13byte 14byte 1500000000000000000000000000000000byte 16byte 17byte 18byte 1900000000000000000000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000001byte 24byte 25byte 26byte 2700100000000000010000110110111000byte 28byte 29byte 30byte 3100000000000000000000000000000000byte 32byte 33byte 34byte 3500000000000000000000000000000000byte 36byte 37byte 38byte 3900000000000000000000000000000010version6traffic-class0flow-label0x12345payload-length4next-header17->UDPhop-limit64source2001:db8::1(cont.)(cont.)(cont.)destination2001:db8::2(cont.)(cont.)(cont.)

Source comes before destination

In this fixed header, the source address field comes before the destination address field.

source bits=128\text{source bits}=128
Source addressThe source and destination addresses are decoded from the fixed header.Source address320 bits / 40 bytes0x600123450004114020010db800000000000000000000000120010db8000000000000000000000002byte 0byte 1byte 2byte 301100000000000010010001101000101byte 4byte 5byte 6byte 700000000000001000001000101000000byte 8byte 9byte 10byte 1100100000000000010000110110111000byte 12byte 13byte 14byte 1500000000000000000000000000000000byte 16byte 17byte 18byte 1900000000000000000000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000001byte 24byte 25byte 26byte 2700100000000000010000110110111000byte 28byte 29byte 30byte 3100000000000000000000000000000000byte 32byte 33byte 34byte 3500000000000000000000000000000000byte 36byte 37byte 38byte 3900000000000000000000000000000010version6traffic-class0flow-label0x12345payload-length4next-header17->UDPhop-limit64source2001:db8::1(cont.)(cont.)(cont.)destination2001:db8::2(cont.)(cont.)(cont.)

Summary

The source address is not prose; it is recomputed from the header bytes.

src=0x20010db8000000000000000000000001\text{src}=0x20010db8000000000000000000000001
Source addressThe source and destination addresses are decoded from the fixed header.Source address320 bits / 40 bytes0x600123450004114020010db800000000000000000000000120010db8000000000000000000000002byte 0byte 1byte 2byte 301100000000000010010001101000101byte 4byte 5byte 6byte 700000000000001000001000101000000byte 8byte 9byte 10byte 1100100000000000010000110110111000byte 12byte 13byte 14byte 1500000000000000000000000000000000byte 16byte 17byte 18byte 1900000000000000000000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000001byte 24byte 25byte 26byte 2700100000000000010000110110111000byte 28byte 29byte 30byte 3100000000000000000000000000000000byte 32byte 33byte 34byte 3500000000000000000000000000000000byte 36byte 37byte 38byte 3900000000000000000000000000000010version6traffic-class0flow-label0x12345payload-length4next-header17->UDPhop-limit64source2001:db8::1(cont.)(cont.)(cont.)destination2001:db8::2(cont.)(cont.)(cont.)