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Quizzes > Computers & IT

What is the IPv6 prefix for 2001:db8:bc15:a:12ab::1/64?

Quick, free quiz to test IPv6 subnetting. Find the IPv6 prefix for 2001:db8. Instant results.

Editorial: Review CompletedCreated By: Anjila BistaUpdated Aug 25, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for Free CCNA IPv6 subnetting quiz on sky blue background with host address text and network icons

This quiz helps you find the correct IPv6 prefix for host 2001:db8:bc15:a:12ab::1/64 and check your subnetting steps. Work through the bits, confirm your math, and see instant feedback. For more practice, try our ip subnetting practice, build basics with the ip networking fundamentals quiz, or review IPv4 in the ip address quiz.

What is the prefix length of the IPv6 address 2001:db8:bc15:a:12ab::1/64?
/128
/48
/64
/56
The notation "/64" after the IPv6 address indicates that the first 64 bits are the network prefix and the remaining 64 bits are host bits. This is the most common subnet size used for IPv6 LAN segments. A /48 would represent the global routing prefix length per site, and /128 denotes a single host.
How many bits are allocated for host addressing within a /64 IPv6 subnet?
16 bits
32 bits
64 bits
128 bits
A /64 prefix leaves 128 - 64 = 64 bits for the interface identifier (host portion). This large host space is designed to support Stateless Address Autoconfiguration (SLAAC) and plenty of end nodes. Smaller host fields like 16 or 32 bits do not comply with the standard IPv6 LAN recommendations.
What is the network prefix of the address 2001:db8:bc15:a:12ab::1/64?
2001:db8:bc15:a:0:0::/64
2001:db8:bc15:a:12ab::/64
2001:db8:bc15:a::/64
2001:db8::/64
To determine the network prefix, you zero out the lower 64 bits (interface identifier) of the address. The first four hextets (2001:db8:bc15:a) remain unchanged, giving 2001:db8:bc15:a::/64. The other options either include part of the host field or shorten the network incorrectly.
In the address 2001:db8:bc15:a:12ab::1/64, which hextet represents the subnet ID according to RFC standards?
bc15
a
12ab
db8
RFC 4291 recommends a 48-bit global routing prefix followed by a 16-bit subnet ID. Here, 2001:db8:bc15 is the global routing prefix (48 bits) and the next 16-bit hextet "a" is the subnet ID. The bc15 hextet is part of the global routing prefix, and 12ab is part of the interface identifier.
What type of IPv6 address block is 2001:db8::/32?
Documentation prefix
Unique local
Global unicast
Link-local
The block 2001:db8::/32 is reserved by RFC 3849 for documentation and examples. It should never be used in production networks. Global unicast addresses normally start at 2000::/3. Link-local uses fe80::/10, and unique local uses fc00::/7.
Which of these is a valid unicast address in the same /64 network as 2001:db8:bc15:a:12ab::1?
2001:db8:bc15:a::1234
2001:db8:bc15:b::1
fe80::1
2001:db8:bc15:0:a::1
A valid unicast address in the same /64 will share the first four hextets (2001:db8:bc15:a). Option 2001:db8:bc15:b::1 is in a different subnet (/64 with 4th hextet b), 2001:db8:bc15:0:a::1 changes the 3rd hextet, and fe80::1 is link-local scope.
How many bits are in each individual hextet of an IPv6 address?
4 bits
8 bits
16 bits
64 bits
An IPv6 address is composed of eight hextets, each hextet representing 16 bits (4 hexadecimal digits × 4 bits each). Four bits correspond to a single hexadecimal digit. The total IPv6 address is 128 bits.
What is the standard length of the interface identifier in an IPv6 /64 subnet?
64 bits
48 bits
32 bits
128 bits
In a /64 subnet, the first 64 bits are used for the network prefix and the remaining 64 bits are used as the interface identifier. This design enables Stateless Address Autoconfiguration (SLAAC). Other lengths do not align with the standard /64 subnet recommendation.
How many /80 subnets can you create within the /64 network 2001:db8:bc15:a::/64?
65,536
16
18,446,744,073,709,551,616
256
Going from a /64 to a /80 uses an extra 16 bits for subnetting (80 ? 64 = 16), so you have 2^16 = 65,536 possible /80 subnets. The other numbers either reflect fewer bits or the entire 128-bit space.
What is the scope of the IPv6 prefix fe80::/10?
Link-local
Multicast
Global
Unique local
IPv6 link-local addresses are assigned from the fe80::/10 block and are valid only on the local link. They are automatically configured and not routable beyond the local segment. Global unicast and unique local have different prefixes, and multicast uses ff00::/8.
How many bits make up the global routing prefix in a standard IPv6 /64 subnet?
32 bits
64 bits
48 bits
16 bits
RFC 6177 recommends a 48-bit global routing prefix followed by a 16-bit subnet ID for typical IPv6 allocation. The remaining 64 bits are used for interface identifiers. Some providers allocate /56 or /32, but /48 is common.
What is the solicited-node multicast address for 2001:db8:bc15:a:12ab::1?
ff02::1:12ab:1
ff02::1:ffab:0001
ff02::1:ffab:1
ff02::1:ff00:1
The solicited-node multicast address is formed as ff02::1:ffXX:XXXX, where XX:XXXX are the low-order 24 bits of the unicast address. Here, the low 24 bits equate to 0x000001, giving ff02::1:ff00:1. This special multicast replaces broadcast in IPv6.
What is the first assignable host address in the 2001:db8:bc15:a::/64 network?
2001:db8:bc15:a::1
2001:db8:bc15:a::2
2001:db8:bc15:a::ffff
2001:db8:bc15:a::0
The network address itself is 2001:db8:bc15:a::/64, so the first usable host address increments the interface identifier by one, giving ::1. Addresses ::0 and the all-ones (::ffff) are invalid for typical host assignment.
Which IPv6 prefix size is recommended for typical LAN segments to enable SLAAC?
/64
/48
/56
/128
IPv6 SLAAC requires a /64 prefix because it uses a 64-bit interface identifier for address autoconfiguration. Using a prefix other than /64 can break SLAAC and related functions. /56 and /48 are typical upstream allocations but not for LAN segments.
How many hextets does an IPv6 address contain?
16
8
4
6
An IPv6 address is composed of eight 16-bit blocks called hextets. Each hextet is represented by four hexadecimal digits. This yields a total of 128 bits for the full address.
What is the correct abbreviation for the hextet 000a in IPv6 notation?
a
10
000a
00a
Leading zeros in a hextet can be omitted, so 000a becomes simply "a". Hexadecimal 0x000a equals decimal 10, but IPv6 requires hex notation. Abbreviating to "00a" is not valid because each omitted digit must be leading.
If you need 256 subnets from 2001:db8:bc15:a::/64, what prefix length should each subnet be?
/56
/72
/68
/64
To create 256 subnets within a /64, you need 8 extra bits for subnetting (2^8 = 256). Therefore, increase the prefix length by 8 bits: 64 + 8 = /72. A /56 or /68 would yield too few or too many addresses.
Which of these represents the concept of broadcast addressing in IPv6?
IPv6 has no broadcast; it uses multicast instead
IPv6 uses the address ::FFFF for broadcast
FF02::2:FFxx:xxxx
FF02::1:FFxx:xxxx
IPv6 eliminates broadcast and uses special multicast addresses for group communication. The all-nodes multicast ff02::1 replaces the broadcast function. The other options mix solicited-node multicast and incorrect constructs.
What is the binary representation of the hextet bc15?
1100110011001100
1011110000010111
1111000010101011
1011110000010101
Hexadecimal BC15 converts to binary by converting each hex digit: B=1011, C=1100, 1=0001, 5=0101, resulting in 1011110000010101. The other options misplace bits.
Which multicast address is used by all DHCPv6 servers on the local link?
ff02::1:3
ff02::1:2
ff05::1:2
ff0e::1:2
DHCPv6 uses the all-DHCP-servers multicast group ff02::1:2 on the local link. ff05::1:2 is site-local, ff02::1:3 is all-DHCP-relays, and ff0e::1:2 is global-scope which is not used.
In SLAAC EUI-64 addressing, which bit is flipped in the interface identifier?
Universal/Local bit
Multicast bit
Link-local flag
Global routing bit
EUI-64 generation flips the seventh bit (the Universal/Local bit) of the interface identifier's first byte to mark it as locally administered. The other bits remain unchanged. This process helps derive the IID from a MAC address.
What is the EUI-64 interface ID for the MAC address 00:1A:2B:3C:4D:5E?
001A:2BFF:FE3C:4D5E
021A:2BFF:FE5E:3C4D
021A:2BFF:FE3C:5E4D
021A:2BFF:FE3C:4D5E
To form the EUI-64 IID, split the MAC (00:1A:2B and 3C:4D:5E), insert FF:FE in the middle, and flip the Universal/Local bit in the first byte (00 ? 02). This yields 021A:2BFF:FE3C:4D5E.
How many /64 subnets can you create from a /48 prefix?
4,294,967,296
65,536
256
1,048,576
A /48 prefix to /64 uses 16 additional bits for subnetting, so 2^16 = 65,536 subnets. The other values correspond to other bit differences and are not correct for /48 to /64.
What summary prefix aggregates 2001:db8:bc15:a::/64 and 2001:db8:bc15:b::/64?
2001:db8:bc15::/61
2001:db8:bc15::/62
2001:db8:bc15::/63
2001:db8:bc15::/64
The two networks differ only in the last bit of the fourth hextet (a=1010, b=1011). They share the first 63 bits, so the summary prefix is /63. A /62 would encompass a:d..f, and /64 is too narrow.
What happens to SLAAC if you configure an IPv6 prefix longer than /64 on an interface?
SLAAC fails because the interface identifier is always 64 bits
SLAAC still works normally
Address autoconfiguration switches to DHCPv6
The host uses a shorter /64 anyway
SLAAC assumes a /64 subnet to split the network and interface identifier. If the prefix is longer, hosts cannot derive their 64-bit IID, causing SLAAC to fail. DHCPv6 may still work if configured, but SLAAC cannot.
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Study Outcomes

  1. Determine the network prefix for host address 2001:db8:bc15:a:12ab::1/64 -

    Calculate the 64-bit network prefix and interpret IPv6 prefix notation to pinpoint the correct subnet.

  2. Analyze IPv6 subnetting practice quiz scenarios -

    Break down different /64 subnets, validate prefix boundaries, and ensure accurate network segmentation.

  3. Apply CCNA Chapter 9 subnetting questions to real-world scenarios -

    Translate theoretical IPv6 subnetting concepts into practical designs for enterprise networks.

  4. Understand broadcast domain quiz principles in IPv6 -

    Explore how IPv6 replaces traditional broadcasts with multicast and grasp domain segmentation techniques.

  5. Differentiate between host ID and network ID in IPv6 addressing -

    Identify and separate the network portion from the interface identifier within an IPv6 address.

  6. Practice CCNA IPv6 addressing exercises through targeted prefix drills -

    Reinforce proficiency by repeatedly determining prefixes for diverse IPv6 host addresses.

Cheat Sheet

  1. IPv6 Address Anatomy -

    IPv6 addresses are 128 bits long and split into eight 16-bit blocks written in hexadecimal (RFC 4291). By answering "what is the prefix for the host address 2001:db8:bc15:a:12ab::1/64?" you'll internalize that a /64 prefix covers the first four hextets. This clear structure is essential for any IPv6 subnetting practice quiz or CCNA IPv6 addressing practice.

  2. Calculating the /64 Network Prefix -

    With a /64 mask, simply zero out the lower 64 bits of the host address to find the prefix (Cisco CCNA Chapter 9 subnetting questions guide). Using bitwise AND on each hextet confirms 2001:db8:bc15:a:12ab::1/64 yields 2001:db8:bc15:a::/64. This method is the cornerstone of any CCNA IPv6 addressing practice and reduces errors on your broadcast domain quiz.

  3. Why /64 is the Standard Segment Size -

    IPv6 leverages a /64 prefix for SLAAC (Stateless Address Autoconfiguration) and Neighbor Discovery Protocol, eliminating traditional broadcast domains (RFC 4862). Understanding this design choice helps you excel on IPv6 subnetting practice quizzes and CCNA Chapter 9 exam scenarios. Remember, every local LAN segment in IPv6 is expected to be /64 by best practices.

  4. Hexet to Binary Conversion Trick -

    Memorize "F=1111, A=1010, 0=0000" as your go-to hextet mnemonic when converting to binary for subnet masks. Practicing this pattern makes answering "what is the prefix for the host address 2001:db8:bc15:a:12ab::1/64?" lightning-fast in timed quizzes. This simple mnemonic is backed by numerous university networking labs and vendor whitepapers.

  5. Hands-On Lab Reinforcement -

    Simulate networks in Packet Tracer or GNS3 using addresses like 2001:db8:bc15:a:12ab::1/64 to solidify your understanding of real-world IPv6 addressing. Doing so reinforces the concept in broadcast domain quiz scenarios and CCNA IPv6 addressing practice questions. Consistent lab work is cited by Cisco Learning and academic research as the top way to master IPv6 subnetting.

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