MAC Addresses: The Complete Guide — Layer 2, CAM Table, ARP, and Security

Thu, 16 Jul 2026 00:00:00 +0000

This article builds on the RJ45 guide. In that guide, we discussed copper, twisted-pair cables, and crimping: the physical layer. Here, we’re moving up a level—just one, but the one everyone skips. Between the cable and the IP address, there’s an entire layer that most people pass through without noticing it: Layer 2, the layer of MAC addresses.

And that’s a shame, because that’s where a good half of everyday network incidents are resolved, and where attacks that haven’t aged a bit in thirty years are carried out.

RJ45: The Complete Guide — Standards, Cable Categories, Connectors, and Tools

Sun, 12 Jul 2026 00:00:00 +0000

This article is in response to a request from @Menvé, a site member and cybersecurity instructor: his students were looking for a clear and comprehensive guide on the RJ45. Because we often forget—especially when we’re just starting out in cybersecurity—but it all starts here: the physical layer is the foundation on which everything else rests. It’s hard to understand segmentation, VLANs, or 802.1X without knowing what’s actually traveling through the cables. For segmentation and VLANs, you can also check out @SilenS’s excellent articlehttps://aperturezone.fr/posts/cisco-firewall-final/

Ethernet on Aperture Zone

MAC Addresses: The Complete Guide — Layer 2, CAM Table, ARP, and Security

RJ45: The Complete Guide — Standards, Cable Categories, Connectors, and Tools