Ethernet operates primarily at Layer 2 (Data Link Layer) of the OSI model, though it has components that touch both Layer 1 (Physical) and Layer 3 (Network). As developers working with network protocols, understanding this distinction is crucial for proper packet handling and network interface programming.

When sending data through Ethernet, programmers interact with MAC addresses rather than IP addresses at this layer. Here's a Python example using Scapy to create a basic Ethernet frame:

from scapy.all import *

eth_pkt = Ether(dst="ff:ff:ff:ff:ff:ff", src="00:11:22:33:44:55")/IP(dst="192.168.1.1")/ICMP()
sendp(eth_pkt, iface="eth0")

When working with raw sockets or network drivers, you'll often need to handle Ethernet headers directly. This C code snippet demonstrates accessing the Ethernet header:

struct ethhdr {
    unsigned char h_dest[ETH_ALEN];
    unsigned char h_source[ETH_ALEN];
    __be16 h_proto;
};

void process_packet(unsigned char* buffer) {
    struct ethhdr *eth = (struct ethhdr *)buffer;
    printf("Destination MAC: %.2X-%.2X-%.2X-%.2X-%.2X-%.2X\n",
        eth->h_dest[0], eth->h_dest[1], eth->h_dest[2],
        eth->h_dest[3], eth->h_dest[4], eth->h_dest[5]);
}

Modern Ethernet includes several Layer 2 features important for network programming:

• VLAN tagging (802.1Q)
• Link Aggregation (LACP)
• MACsec encryption

Here's how to check VLAN configuration on Linux:

$ ip -d link show eth0
5: eth0:  mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 00:11:22:33:44:55 brd ff:ff:ff:ff:ff:ff promiscuity 0 
    vlan protocol 802.1Q id 100  

When debugging Ethernet issues, these commands are essential:

# Check MAC address table (on switches)
$ bridge fdb show

# Monitor Layer 2 traffic
$ tcpdump -i eth0 -e -n

Ethernet operates at both Layer 1 (Physical) and Layer 2 (Data Link) of the OSI model. As developers, understanding this dual-layer functionality is crucial when working with network protocols or debugging connectivity issues. The IEEE 802.3 standard defines Ethernet's specifications, making it one of the most widely implemented LAN technologies.
At the physical layer, Ethernet defines:

- Cable types (Cat5, Cat6, fiber optics)

- Signaling methods

- Connector pinouts

- Network topology
Example of checking Ethernet interface in Linux:



$ ip link show

1: lo:  mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default

    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

2: eth0:  mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000

    link/ether 08:00:27:98:dc:9a brd ff:ff:ff:ff:ff:ff


The Data Link layer is where Ethernet truly shines with:

- MAC addressing

- Frame formatting

- Error detection

- Flow control
Here's how to examine Ethernet frames using Python with Scapy:



from scapy.all import *

def packet_callback(packet):

    if packet.haslayer(Ether):

        print(f"Source MAC: {packet[Ether].src}")

        print(f"Destination MAC: {packet[Ether].dst}")

        print(f"EtherType: {hex(packet[Ether].type)}")

sniff(prn=packet_callback, count=5)


When programming network applications, consider these Ethernet characteristics:

- Standard MTU of 1500 bytes

- CSMA/CD arbitration (for half-duplex)

- VLAN tagging (802.1Q)

- Jumbo frame support
Example C code for raw Ethernet socket:



#include 

#include 
#include 
#include 

int main() {

    int sock = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

    if (sock < 0) {
        perror("socket");
        return 1;
    }
    
    // Continue with packet processing...
    close(sock);
    return 0;
}

Contemporary implementations include:

- 10 Gigabit Ethernet (10GBASE-T)

- Power over Ethernet (PoE)

- Automotive Ethernet

- Time-Sensitive Networking (TSN)