Apr 16, 2020 · This is a fun question with a lot of history. Originally, the EtherType field indicated the length of the frame; not the type of payload. The relevant Wikipedia article contains a good explanation with references. MPLS is an example of a protocol which lacks a field indicating the payload type. This has important consequences!

Jul 1, 2018 · Ethertype/length actually indicating the frame length is pretty much obsolete, it's redundant. Instead, the frame end is signaled on the physical layer by loss of carrier or a special end-of-data symbol (depending on the specific PHY).

Mar 5, 2024 · EtherType is a mandatory field, you can't skip it. With Ethernet, you cannot use values below 0x0600 as that would indicate the payload length (up to 0x5DC) or be undefined (0x5DD-0x5FF) - see IEEE 802.3 3.2.6. You can view the official list of EtherType values here. I'd suggest one of the "Local Experimental" EtherTypes for your purpose - the ...

0x8100 is standard ethertype for single tagged frames (802.1Q), it can be used(and it is) for QinQ tunneling but you should be careful with other vendors configuration, as defaults vary. 0x88a8 is the standardized value for QinQ (802.1ad) and I would suggest to use this type instead of 0x9100(non-standard QinQ ethertype), especially in a ...

Apr 4, 2018 · There is no Ethertype for Spanning-Tree protocol BPDUs - they are encapsulated in 802.3 Ethernet (rather than Ethernet II), and so the Ethertype field does not exist. See What is the difference between Ethernet II and 802.3 Ethernet? for more information

Jan 24, 2020 · The EtherType field contains the length of the data including these 3 or 4 bytes. In the most common case, the first byte after the EtherType field is an even value describing the packet type, which is followed by a byte with the same value or the value plus 1.

Nov 14, 2022 · That EtherType is (was) used for the Ethernet configuration testing protocol (CTP) which is somewhat similar to IP's ping (ICMP echo) facility but for the data link layer. I don't think it ever gained wide support though.

Jun 15, 2019 · frame.protocols=eth:ethertype:ip:udp:data These frames have: frame.protocols=eth:ethertype:ip:data Examining the ip.version and ip.proto fields of these frames in order to make sure that they are in fact UDP datagrams, I see, as expected: ip.version=4 # IPv4 ip.proto=17 # UDP

Feb 13, 2020 · The "Ethertype or length" field is how you tell whether it is EthernetII or 802.3. If the field is less than 1500 then it means that the frame is 802.3 and the field specifies the length. So when you put 0x0027 in that field, you are saying that your frame is 802.3 ethernet and it's length is 39 octets.

Jul 18, 2020 · The switch examines EtherType, to see if the frame is a special frame called a Bridge Protocol Data Unit. Those frames are valid only between switch neighbours and they go to the CPU of the switch. All other traffic takes the forwarding path; that is, to the egress queue indicated by the destination MAC address in that VLAN's MAC address table.