While both MAC and IP addresses serve as network identifiers, they operate at different layers of the networking stack with distinct purposes:

// Example showing both addresses in a packet
struct EthernetHeader {
    uint8_t dest_mac[6];
    uint8_t src_mac[6];
    uint16_t ethertype;
};

struct IPHeader {
    uint8_t version_ihl;
    uint8_t dscp_ecn;
    uint16_t total_length;
    // ... other IP fields ...
    uint32_t src_ip;
    uint32_t dest_ip;
};

The key architectural difference lies in their structure:

• MAC addresses are flat (00:1A:2B:3C:4D:5E)
• IP addresses are hierarchical (192.168.1.10/24)

This hierarchy enables efficient routing through aggregation:

# Traditional IP routing table
192.168.0.0/16 via 10.0.0.1
192.168.1.0/24 via 10.0.0.2

# Imaginary MAC routing would require:
00:1A:2B:00:00:00/24 via 00:0C:...
00:1A:2B:3C:00:00/16 via 00:0D:...
# ... millions of individual entries

The OSI model clearly separates concerns:

Consider ARP's role in IPv4:

// Simplified ARP resolution process
void send_packet(IPAddress dest_ip) {
    MACAddress dest_mac = arp_cache.lookup(dest_ip);
    if (!dest_mac) {
        // Broadcast ARP request
        send_arp_request(dest_ip);
        // Wait for response
        dest_mac = wait_for_arp_response();
    }
    send_ethernet_frame(dest_mac, payload);
}

Global MAC routing would require:

• No broadcast domains (every ARP would go worldwide)
• Impossible routing table sizes
• No network segmentation capabilities

Think of MAC addresses like social security numbers (unique identifiers) and IP addresses like mailing addresses (routable locations). You wouldn't ship packages using SSNs because:

1. They contain no geographic information
2. The lookup system isn't designed for physical delivery
3. There's no hierarchy to optimize delivery paths

Even IPv6's 128-bit addressing maintains this separation, though it introduces features like SLAAC that blend the layers:

// IPv6 address autoconfiguration from MAC
void generate_eui64(MACAddress mac, IPv6Address *ipv6) {
    // Flip the universal/local bit
    mac[0] ^= 0x02;
    // Insert FF:FE in the middle
    ipv6->bytes[8] = mac[0];
    ipv6->bytes[9] = mac[1];
    ipv6->bytes[10] = mac[2];
    ipv6->bytes[11] = 0xFF;
    ipv6->bytes[12] = 0xFE;
    // ... remaining bytes
}

While both MAC and IP addresses serve as unique identifiers in networking, they operate at different layers of the OSI model and serve distinct purposes:

• MAC addresses (Layer 2) are burned into network hardware and used for local network communication
• IP addresses (Layer 3) are logical addresses designed for routing across multiple networks

The key limitation preventing MAC addresses from replacing IP addresses lies in their flat structure:

// MAC address structure (flat)
00:1A:2B:3C:4D:5E

// IPv4 address structure (hierarchical)
192.168.1.1/24

// IPv6 address structure (hierarchical)
2001:0db8:85a3:0000:0000:8a2e:0370:7334

This hierarchical nature enables efficient routing tables and scalable internet architecture.

Several fundamental issues arise when considering MAC addresses for internetwork communication:

1. No built-in network segmentation: MAC addresses don't contain information about network topology
2. Routing inefficiency: Routers would need to maintain enormous tables of all possible MAC addresses
3. No location information: MAC addresses don't indicate geographic or network location

The TCP/IP protocol stack was specifically designed to solve internetworking challenges that couldn't be addressed by MAC-based solutions:

While pure MAC-based networking isn't feasible, some modern approaches blend concepts:

// Example of MAC address usage in IPv6 (EUI-64)
// Original MAC: 00:1A:2B:3C:4D:5E
// IPv6 Interface ID: 021A:2BFF:FE3C:4D5E

Protocols like IPv6's Stateless Address Autoconfiguration (SLAAC) demonstrate how MAC addresses can complement IP addressing without replacing it.

Understanding these distinctions is crucial when working with network programming:

// Python example showing both address types
import socket
import uuid

# Get MAC address
mac = ':'.join(['{:02x}'.format((uuid.getnode() >> elements) & 0xff) 
               for elements in range(0,2*6,2)][::-1])

# Get IP address
ip = socket.gethostbyname(socket.gethostname())

print(f"MAC: {mac}, IP: {ip}")

This demonstrates how applications typically need to work with both address types for different purposes.