How to parse Ethernet packet header (src & dst MAC addresses) using lwIP

You can use this code, for example, in a custom packet handler function.

#include <lwip/prot/ethernet.h>

eth_hdr* hdr = reinterpret_cast<eth_hdr*>(buffer);
auto srcMAC = hdr->src.addr;
auto dstMAC = hdr->dest.addr;

Serial.printf("Received packet: Packet of length %d\n", len);
Serial.printf("    Src MAC: %02X:%02X:%02X:%02X:%02X:%02X\n", srcMAC[0], srcMAC[1], srcMAC[2], srcMAC[3], srcMAC[4], srcMAC[5]);
Serial.printf("    Dst MAC: %02X:%02X:%02X:%02X:%02X:%02X\n", dstMAC[0], dstMAC[1], dstMAC[2], dstMAC[3], dstMAC[4], dstMAC[5]);
Serial.printf("    Our MAC: %02X:%02X:%02X:%02X:%02X:%02X\n", ourEthernetMAC[0], ourEthernetMAC[1], ourEthernetMAC[2], ourEthernetMAC[3], ourEthernetMAC[4], ourEthernetMAC[5]);