How to calculate the MS NLB multicast mac address from a unicast IP address
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Practical configuration and operational reference for How to calculate the MS NLB multicast mac address from a unicast IP address.
Legacy / version-specific guidance
The original article references Windows Server 2003. It is retained for historical or version-specific use. Confirm applicability to the target product and version before using the procedure.
Procedure
If using Microsoft Network Load Balancing (NLB) set-up in multicast mode you can calculate the multicast mac address from the unicast NLP cluster IP address as follows:
Convert each octet of the unicast IP to Hexadecimal, the multicast mac is 03-bf-WW-XX-YY-ZZ. e.g. IP 199.99.20.70 Convert to Hex:
| Decimal | Hex |
|---|---|
| 199 | c7 |
| 99 | 63 |
| 20 | 14 |
| 70 | 46 |
The multicast mac address would then be:
03-bf-c7-63-14-46