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Networking Fundamentals · Intermediate

Modified EUI-64

A method that builds a 64-bit IPv6 interface ID from a 48-bit MAC address by inserting fffe in the middle and flipping the seventh bit.

Definition

The MAC is split into two 24-bit halves, ff:fe is inserted between them, and the universal/local bit (the seventh bit of the first byte) is inverted. Cisco routers use EUI-64 by default for link-local addresses and when ipv6 address prefix/64 eui-64 is configured.

Example

MAC 00:1a:2b:3c:4d:5e becomes interface ID 021a:2bff:fe3c:4d5e.

Exam tip

Flip the 7th bit: 00 becomes 02 and 02 becomes 00; look for ff:fe in the middle to spot EUI-64.

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