The Inserted Tag

Destination and Source

A tagged Ethernet frame still begins with destination and source MAC addresses.

highlighted = computed this step

Ethernet still starts with two MACs

A tagged Ethernet frame still begins with destination MAC and source MAC.

dst=0xaabbccddeeff,src=0x001122334455\text{dst}=0xaabbccddeeff,\quad \text{src}=0x001122334455
Destination and sourceThe VLAN tag is decoded from the pinned Ethernet frame bytes.Destination and source160 bits / 20 bytes0xaabbccddeeff0011223344558100002a08004500byte 0byte 1byte 2byte 310101010101110111100110011011101byte 4byte 5byte 6byte 711101110111111110000000000010001byte 8byte 9byte 10byte 1100100010001100110100010001010101byte 12byte 13byte 14byte 1510000001000000000000000000101010byte 16byte 17byte 18byte 1900001000000000000100010100000000dst-mac0xaabbccddeeff(cont.)(cont.)src-mac0x001122334455tpid0x8100tci0x002ainner-ethertype0x0800payload-marker0x4500

Destination MAC

The destination MAC is 0xaabbccddeeff.

dst=0xaabbccddeeff\text{dst}=0xaabbccddeeff
Destination and sourceThe VLAN tag is decoded from the pinned Ethernet frame bytes.Destination and source160 bits / 20 bytes0xaabbccddeeff0011223344558100002a08004500byte 0byte 1byte 2byte 310101010101110111100110011011101byte 4byte 5byte 6byte 711101110111111110000000000010001byte 8byte 9byte 10byte 1100100010001100110100010001010101byte 12byte 13byte 14byte 1510000001000000000000000000101010byte 16byte 17byte 18byte 1900001000000000000100010100000000dst-mac0xaabbccddeeff(cont.)(cont.)src-mac0x001122334455tpid0x8100tci0x002ainner-ethertype0x0800payload-marker0x4500

Source MAC

The source MAC is 0x001122334455. The tag comes after these two addresses.

src=0x001122334455\text{src}=0x001122334455
Destination and sourceThe VLAN tag is decoded from the pinned Ethernet frame bytes.Destination and source160 bits / 20 bytes0xaabbccddeeff0011223344558100002a08004500byte 0byte 1byte 2byte 310101010101110111100110011011101byte 4byte 5byte 6byte 711101110111111110000000000010001byte 8byte 9byte 10byte 1100100010001100110100010001010101byte 12byte 13byte 14byte 1510000001000000000000000000101010byte 16byte 17byte 18byte 1900001000000000000100010100000000dst-mac0xaabbccddeeff(cont.)(cont.)src-mac0x001122334455tpid0x8100tci0x002ainner-ethertype0x0800payload-marker0x4500

Summary

The tag does not replace the Ethernet addresses; it is inserted after them.

MAC bytes=12\text{MAC bytes}=12
Destination and sourceThe VLAN tag is decoded from the pinned Ethernet frame bytes.Destination and source160 bits / 20 bytes0xaabbccddeeff0011223344558100002a08004500byte 0byte 1byte 2byte 310101010101110111100110011011101byte 4byte 5byte 6byte 711101110111111110000000000010001byte 8byte 9byte 10byte 1100100010001100110100010001010101byte 12byte 13byte 14byte 1510000001000000000000000000101010byte 16byte 17byte 18byte 1900001000000000000100010100000000dst-mac0xaabbccddeeff(cont.)(cont.)src-mac0x001122334455tpid0x8100tci0x002ainner-ethertype0x0800payload-marker0x4500