Even Private Fiber Needs Encryption
You might assume that a private, dedicated fiber connection is inherently secure — after all, it's not the public internet. This assumption is partially correct but incomplete.
Your Direct Connect traffic still travels through a colocation facility that houses equipment from hundreds of other companies. The fiber runs through shared conduits, patch panels, and intermediate equipment. A sophisticated adversary — a nation-state actor, for example — could potentially tap the fiber physically or compromise equipment in the facility. For most organizations, this risk is theoretical. For government agencies, financial institutions, and healthcare organizations handling highly sensitive data, it is a real compliance requirement.
MACsec (Media Access Control Security) is the solution. It is a standard (IEEE 802.1AE) that provides point-to-point encryption at Layer 2 — the Data Link layer of the OSI model.
How it works:
- MACsec encrypts data at the network interface hardware level, as it leaves the physical port of your router.
- The encryption happens before the data even enters the fiber cable.
- The cloud provider's router port decrypts it upon receipt.
- Everything in between — the cross-connect cable, patch panels, intermediate fiber — carries only encrypted ciphertext.
- Uses AES-256-GCM encryption, which provides both confidentiality and integrity (tamper detection).
The critical advantage over VPN encryption:
VPN encryption (IPSec) happens in software, consuming CPU cycles on your router. At high speeds (10 Gbps, 100 Gbps), software encryption becomes a bottleneck — your router's CPU cannot encrypt packets fast enough to keep up with the line rate.
MACsec uses dedicated hardware chips called ASICs (Application-Specific Integrated Circuits) built into the router's physical ports. These chips encrypt at line rate — the full speed of the physical link — with zero CPU overhead and zero performance penalty.
Requirements: Both your router and the cloud provider's router must support MACsec. AWS supports MACsec on dedicated 10 Gbps and 100 Gbps Direct Connect connections. You need a MACsec-capable router (such as Cisco ASR 9000 series or Juniper MX series).
A common interview question is: "You have a 10 Gbps Direct Connect link and a compliance requirement for encryption in transit. Why not just run IPSec VPN over the Direct Connect?" The answer has two parts: (1) IPSec software encryption would bottleneck at 2-4 Gbps on most routers, wasting most of your 10 Gbps capacity; (2) MACsec encrypts at hardware line rate with zero performance penalty, making it the correct solution for high-speed dedicated links. This demonstrates understanding of where encryption happens in the stack and its performance implications.
Key Point: MACsec encrypts at hardware line rate at Layer 2, providing full-speed encryption on Direct Connect links without the CPU bottleneck of VPN-based encryption. It is the appropriate choice when you need both the performance of Direct Connect and the encryption assurance required by compliance frameworks.