MAC Address Validator

Validate MAC (Media Access Control) addresses.

Input

Output

Examples

Example 1

01:23:45:67:89:AB

Example 2

01-23-45-67-89-AB

Example 3

0123.4567.89AB

MAC Address Structure and Formats

MAC addresses are 48-bit (6-byte) hardware identifiers assigned to network interfaces. They consist of 12 hexadecimal digits, with the first half being the OUI (Organizationally Unique Identifier) assigned to manufacturers, and the second half being device-specific.

Multiple notation formats exist: Colon-separated (01:23:45:67:89:AB), hyphen-separated (01-23-45-67-89-AB), dot-separated Cisco format (0123.4567.89AB), and no separator (0123456789AB). Network tools use different formats, requiring validators to accept all variations.

The first octet contains two special bits: bit 0 indicates unicast (0) or multicast (1), and bit 1 indicates globally unique (0) or locally administered (1). These bits help identify address types and whether the MAC is manufacturer-assigned or manually configured.

Why MAC Address Validation Matters

Network access control (NAC) systems use MAC addresses for device authentication. Invalid MAC entries in allowlists prevent legitimate devices from connecting, while typos in blocklists fail to exclude unwanted devices. Validation prevents security gaps and access issues.

DHCP reservation configurations map MAC addresses to static IPs. Mistyped MACs cause reservations to fail, resulting in devices getting wrong IPs or no network access. Validating before saving DHCP configurations prevents connectivity problems.

Network monitoring tools track devices by MAC address. Invalid entries break correlation between events, making troubleshooting difficult. Asset management systems also depend on accurate MACs for inventory tracking and hardware lifecycle management.

MAC Address Validation and Normalization

Normalize MAC addresses before storage by converting to a standard format—typically lowercase with colons. This prevents duplicate entries from format variations (01:23:45:67:89:AB vs 01-23-45-67-89-ab) and simplifies searching and comparison.

Validate hexadecimal characters only (0-9, A-F). Reject addresses with invalid characters or wrong length. Some systems accept shortened formats for zero-padding, but strict validation prevents ambiguity and ensures compatibility across network tools.

Check for reserved addresses: All zeros (00:00:00:00:00:00) is invalid, broadcast (FF:FF:FF:FF:FF:FF) has special meaning. Multicast addresses (first octet odd) shouldn't be assigned to physical interfaces. Warn users about these special cases.

Consider EUI-64 format for IPv6: MAC addresses convert to 64-bit interface identifiers by inserting FF:FE in the middle. If your tool supports IPv6 address generation, validate that the source MAC is suitable for conversion.

MAC Address Practical Applications

Wi-Fi access points use MAC filtering for security, though it's easily spoofed. Validate MAC lists to ensure typos don't accidentally lock out administrators or fail to block unwanted devices. Document that MAC filtering provides minimal security.

Switch port security limits MACs allowed per port to prevent MAC flooding attacks. Validate configured addresses and set appropriate violation actions. Invalid MACs in port security configs cause legitimate traffic to be dropped.

Virtual networking requires MAC address assignment to VMs and containers. Hypervisors generate MACs automatically, but manual assignment requires validation to avoid conflicts. Overlapping MACs cause network chaos with unpredictable routing.

OUI lookup databases map MAC prefixes to manufacturers. After validating format, the first six digits identify the vendor. This helps with asset discovery, inventory management, and identifying rogue devices on networks.

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