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Difficulty: MediumIPv6 Addressing and Prefixes

A network administrator configures an interface on a Cisco router with the IPv6 address `2001:db8:3c4d:15::1/64`. Which of the following IPv6 addresses resides within the exact same `/64` subnet prefix as this interface?

  1. 2001:db8:3c4d:15:a::1Answer
  2. B
    2001:db8:3c4d:1500::1
  3. C
    2001:db8:3c4d:15::1::a
  4. D
    2001:db8:3c4d:1::1

Answer

The address 2001:db8:3c4d:15:a::1 resides in the 2001:db8:3c4d:15::/64 subnet prefix.
The configured interface address 2001:db8:3c4d:15::1/64 uses the network prefix 2001:db8:3c4d:15::/64 (fully expanded as 2001:0db8:3c4d:0015::/64). The address 2001:db8:3c4d:15:a::1 expands to 2001:0db8:3c4d:0015:000a:0000:0000:0001, sharing the exact same 64-bit network prefix.

Step-by-Step Solution

1
Determine the network prefix of the configured IPv6 address
The configured address 2001:db8:3c4d:15::1/64 has a prefix length of /64. Expanding leading zeros gives 2001:0db8:3c4d:0015::1/64. The first 64 bits (4 hextets) represent the network prefix: 2001:0db8:3c4d:0015::/64 (or 2001:db8:3c4d:15::/64).
The prefix length /64 specifies that the first 64 bits determine subnet membership.
2
Expand and evaluate the candidate IPv6 options
Expanding 2001:db8:3c4d:15:a::1 yields 2001:0db8:3c4d:0015:000a:0000:0000:0001. The first 64 bits match 2001:0db8:3c4d:0015 exactly.
IPv6 address compression rules allow leading zeros to be omitted in hextets and contiguous zero hextets to be replaced with :: once.

Key Concept

IPv6 Address Representation and Subnet Prefix Matching
Estimated Time:1m 0s
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Topics

IPv6 Addressing and Prefixes

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