Cisco CCNA (200-301)Network FundamentalsMedium
An engineer examines the IPv6 address 2001:DB8:ACAD:1::10/64 assigned to a server's interface. Which portion of this address represents the interface identifier (host portion)?
- AThe last 64 bits (0000:0000:0000:0010)
- BACAD:1
- CThe first 48 bits only
- D2001:DB8 only
Show answer & explanationAnswer & explanation
Correct answer: A. The last 64 bits (0000:0000:0000:0010)
With a /64 prefix, the first 64 bits (2001:DB8:ACAD:1) form the network/subnet portion, and the remaining 64 bits are the interface identifier that uniquely identifies the host on that subnet. In this address, that portion is 0000:0000:0000:0010.
Why the other options are wrong
- B. This is part of the subnet ID within the /64 prefix, not the interface ID.
- C. 48 bits alone does not equal the /64 boundary used for the interface ID split.
- D. This represents only part of the global routing prefix, not the full network portion.
IPv6 /64 Addressing Structure
A standard IPv6 unicast address is split into a 64-bit network prefix and a 64-bit interface identifier that uniquely addresses the host.
- Global routing prefix + subnet ID = 64 bits
- Interface ID = remaining 64 bits
- Common /64 boundary for LANs
- EUI-64 or random methods generate interface ID
Memory trick: IPv6 splits in half: 64 for network, 64 for host.