A Network Interface Card provides the physical interface between a device and the network, handling the conversion between digital data and network signals.
Why it matters
- Every networked device needs a NIC to communicate.
- MAC addresses from NICs are used for network access control.
- Network performance often depends on NIC capabilities.
- Security features like Wake-on-LAN and PXE boot rely on NIC functionality.
Key concepts
- MAC address: 48-bit hardware address uniquely identifying each NIC (format: AA:BB:CC:DD:EE:FF).
- OUI (Organizationally Unique Identifier): First 24 bits identify the manufacturer.
- Speed: Common speeds are 1 Gbps (gigabit) and 10 Gbps.
- Duplex: Full-duplex allows simultaneous send/receive; half-duplex alternates.
Types of NICs
- Ethernet: Wired connection using RJ-45 connectors.
- Wireless (WLAN): Wi-Fi connectivity via 802.11 standards.
- Fiber: High-speed connections using optical cables.
- Virtual NICs: Software-defined interfaces for VMs and containers.
Security considerations
- MAC filtering: Limiting network access to known MAC addresses (easily bypassed via spoofing).
- 802.1X: Port-based network access control requiring authentication.
- Network segmentation: VLANs to isolate traffic.
- Promiscuous mode: Allows NIC to capture all network traffic (used for monitoring, also by attackers).
Troubleshooting
- Check link status lights on physical NICs.
- Verify driver installation and updates.
- Test with different cables or ports.
- Use ipconfig/ifconfig to check IP configuration.
- Examine MAC address for hardware issues.
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