Layer2

MACsec (MAC Security, IEEE 802.1AE) is an IEEE standard, first published in 2006 and supported in the Linux kernel since 4.6 (2016), that encrypts and authenticates Ethernet frames at layer 2 — hop by hop between directly connected devices. Its operating layer is what distinguishes it from IPsec (layer 3) and TLS (layer 4): MACsec wraps Ethernet frames, not IP packets or TCP streams, so it can protect every byte that traverses a link segment regardless of what protocol it carries. ARP replies, DHCP offers, LLDP frames, routing protocol adjacencies, and layer-2 broadcast traffic are all encrypted and authenticated alongside application data — something neither IPsec nor TLS can accomplish because both require an IP header to already be present and unenforced. The topology implication of this is that MACsec is link-local and hop-by-hop: it encrypts between two directly adjacent Ethernet peers (a host and a switch, or two switches), decrypts at each hop for forwarding decisions, and re-encrypts toward the next hop. It cannot stretch across a routed boundary; for that, IPsec is the right tool.