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Ethernet Frames

Published Updated 2 min read

An Ethernet frame is the unit of data sent over a wired network. Each frame has a fixed structure: a header identifying the sender and receiver, a payload, and a checksum. This guide walks through that structure field by field.

Anatomy of a frame

Fields in transmission order:

EtherType or length?

The 2 bytes after the MAC addresses depends on its value:

Almost all modern traffic uses an EtherType.

VLAN tags

An optional 4-byte field between the source MAC and EtherType marks the virtual LAN a frame belongs to. Switches use this to separate traffic on shared infrastructure, so tagged frames appear on most enterprise and data centre networks.

Jumbo frames

Some networks support payloads up to around 9000 bytes, well above the standard 1500-byte MTU. The larger size reduces per-byte overhead on high-throughput workloads — common in data centres and storage networks, rare on consumer ones.

Every device along the path must support it, or oversized frames are dropped.

Interactive explorer

Total: 1224 bytes
Header: 14 bytes
Protocol: IPv4
Byte map of the current frame in software order. Software view shows only the bytes the operating system delivers; the preamble and FCS are stripped by the NIC.
DST (6 bytes)DST0SRC (6 bytes)SRC6TYPE (2 bytes)TYPE12PAYLOAD (1210 bytes)PAYLOAD141224
Preamble + SFD8 bytes · 64 bits

7 bytes of clock sync then 1 byte Start Frame Delimiter. Software doesn't see this.

10101010 10101010 10101010 10101010 10101010 10101010 10101010 10101011
Destination MAC6 bytes · 48 bits

Who the frame is addressed to

3c:22:fb:9e:15:2f
Delivery
unicast
Assignment
globally unique
Source MAC6 bytes · 48 bits

Who sent the frame

52:54:00:9b:15:78
Delivery
unicast
Assignment
locally administered
EtherType2 bytes · 16 bits

Protocol type of the payload

0x0800
Protocol
IPv4
Payload1210 bytes · 9680 bits

The packet handed down from the layer above (IP, ARP, …)

2a 58 07 10 22 9d a0 c2 ba 12 54 ad b6 e8 27 17 3d 73 fe 16 9e 44 2b 99 3c 2f 1d a4 11 49 89 55 e7 22 a5 2a b8 b3 c8 4f ea a4 ef ac 67 f0 c2 b2 c4 dc d2 4e 87 7d 01 63 8b a5 b4 b6 d7 bd 91 9d 81 27 4c 88 37 e4 35 be 36 f7 99 da 50 5a 0f ee 4e 05 8b cf a3 7b 3b ba 9a 4f 45 a7 59 48 2b 09 19 7e ac 9f a9 b8 6a 19 ac 7e 0c b1 e9 a0 4a 23 fa 42 b8 1a 5c a6 15 c1 85 34 73 26 79 e6 e0 ba e9 98 81 66 4b 66 68 fe 73 20 b4 9f c3 9c 88 82 af 35 60 02 b5 ba 07 fa 34 4f 2c 7b 28 75 64 d3 39 7c e5 60 20 c5 58 10 a8 e9 f7 6f c3 4e d4 bb a8 47 2b d6 36 93 1c 8f 75 97 51 04 25 0c 99 f8 c7 fb 76 3d ae 72 44 15 ac e5 1c a8 39 19 da 58 4a 83 0f c1 75 4a 30 26 e6 48 8c b3 e4 90 ac 9e 23 08 b6 9e 73 1c fe 82 f9 ab d5 7b 56 40 61 01 17 c7 9c f6 8f 2b db cb e2 8e 9e 86 2d d0 e5 93 92 9c cf 35 57 30 50 0d f6 e1 f9 55 94 9f 5e bd 26 be 28 bd 5a 2f df 51 ee d7 bf da 94 5a 80 80 9b 36 c6 43 27 60 77 a8 bf 0d 74 4a ba 12 5a 38 56 64 82 98 31 36 ef 5f d0 01 bc 40 0f 7c 9c 5c f9 12 50 b7 17 c1 5a 1d e0 32 1a 15 cb 7e 84 f3 03 20 aa 0c 2d 6b 75 f7 a6 b0 08 19 30 0f 10 75 a3 8e 91 d3 06 48 53 b9 e8 b1 ff 84 19 e1 28 5f 92 24 64 df 06 69 ad e3 52 1a 1c c7 10 be cb fb ff 88 c0 6f 4a 45 0f 6c ff 48 f1 b4 12 17 c4 94 b9 3d b8 82 d9 8c df 62 64 43 9b 66 56 dd a8 0b 2b a1 19 2b b3 fa 1f 34 d5 49 23 21 ae 69 7a eb 1f 24 96 9d a0 cd fe cc 01 f5 d7 12 40 29 d5 5d 75 5b 24 28 a5 11 49 7f 27 ab 1f 1d 21 9e 1c b8 d0 c9 66 d0 3e fe 81 cd 18 69 6c 0b 9e 08 4a 28 e4 aa a5 38 b5 2c a8 2e ba 74 3c 9a bd cb 37 96 ed 41 46 81 87 2f 1a 19 f4 80 46 c3 31 6f 4e eb f9 c0 74 c8 4c 6b 09 81 64 59 08 a6 e8 19 40 3e 1b 50 0c 46 0f f5 0d 25 91 39 a8 f1 30 09 b7 65 77 3d 2f 09 4c e9 33 0d 57 89 aa 69 13 08 1f 9f dc c8 d9 47 b5 95 54 c8 e1 3b 60 6b 43 f3 e0 4e 25 b1 c7 69 23 ff 65 7d ba 36 94 b5 3d ff 4b fc 66 d8 c6 32 cf 39 eb 44 e4 90 d7 a9 d8 31 35 4a b8 c8 4c f4 ae cd 9d 01 64 bd ad 6f a1 b0 82 20 30 c2 5b cb 4b 77 1e 85 d8 0a e9 9e df 09 08 60 78 39 d4 21 76 48 4e e6 ac 0b c2 5b b4 fc 1a 01 82 ae 79 fd 79 34 c4 bb ac 78 ee 30 f8 fc 68 d0 8b 95 d5 49 2f cf 36 0c 22 8a e0 d5 00 a1 05 18 1a 04 ef 25 3a d9 15 ae f0 6b 74 ac 25 91 3a 56 88 c1 b5 a8 6c 8c 24 88 aa cf cc 27 66 24 02 5d a3 3e 85 85 06 e9 aa 81 9a 82 50 35 c6 33 29 0e ce 34 25 fd d9 5e 68 e1 ec 93 43 56 10 91 ca ff fe c2 d5 e0 36 df c6 92 fe 0b 97 13 e0 18 39 05 52 a0 0b 36 26 d9 fd dc ed e7 49 23 ab b9 be 04 52 b0 e4 e8 d4 64 b4 3c 8f 1c 61 cb 83 72 df 69 15 23 0f d8 c1 01 a2 f7 a0 8a 64 a8 9c 08 af cd db b6 fc f3 07 be 94 cb 31 39 10 ff 16 2f cd 4e d5 5f 35 4f f3 e5 3e d8 2e f0 2c f2 25 c5 5c d6 be fb fd 22 3f b0 fd 90 b9 cc 14 84 d0 d7 c1 a9 33 90 68 9f 5e 2e 75 08 28 e8 51 fb e3 02 cc 04 e6 c2 75 99 1c ea 42 d9 2a c3 3a 8b 8f cc 0f 93 08 f3 c0 7a b5 47 ae 25 cf 4a c6 97 9e 4a 8f 61 48 6e 5c c9 35 cf dd 4b 38 be 00 88 6a 91 b1 d4 51 48 fc 99 e4 30 d6 16 a6 ac 43 38 84 49 36 6d 52 a5 71 7c cf 04 33 e3 77 52 de c7 b7 01 65 1d 66 42 ac 91 f7 08 e4 9a 93 6d 0d e9 c6 a7 f4 7a 0c 2e 9b cd 94 81 00 af ff 4b 59 a5 ec 11 6e 8f ac c2 d6 6e be 1b 36 06 c5 7e f4 18 19 0e ba fb 75 bf 67 4f 4f ad 72 a9 df e2 a9 60 39 f2 3e 9a 6c 9a dd b4 21 7b e8 9e 19 50 fb 88 81 80 1f 3f 94 f4 cd f1 98 fd d8 d8 2c 62 16 8c 3f de 05 88 ad 5e 80 77 6a b0 b1 61 97 a6 d5 80 3d e8 6d 57 6d cd 68 56 e0 c6 18 3d 88 a2 c0 aa 9a 7f a7 80 2a 0d 08 51 a7 aa b4 96 0d 38 89 1d e4 98 d7 f7 23 4c f0 76 7c 91 d6 bd 04 91 ee 77 2a cb 75 b0 44 7c d0 58 99 0f 19 14 e4 06 ac ca 8e cf 91 51 1c f3 88 cb 64 47 e9 ac 3a ee df c0 7f 98 20 7c 87 25 2b 87 4a 0d 09 7c ef a3 3d 88 3e c8 c4 f0 57 e1 33 7e b9 86 1c 9d b6 09 33 08 14 a8 5a e6 7d 4d ee 21 e4 99 61 a1 9c 75 94 3b bc 48 2c 12 bb e5 bd 68 58 5b 3b 15 05 45
FCS4 bytes · 32 bits

Frame Check Sequence, a CRC-32 checksum of the frame. Software doesn't see this.

63 da 32 5b

References