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200-301 · Question #682

How many bits represent network id in a IPv6 address?

The correct answer is C. 64. In an IPv6 address, the network ID, also known as the network prefix, is conventionally represented by the first 64 bits of the address.

Submitted by yaw92· Mar 5, 2026

Question

How many bits represent network id in a IPv6 address?

Options

  • A32
  • B48
  • C64
  • D128

How the community answered

(54 responses)
  • A
    2% (1)
  • B
    2% (1)
  • C
    91% (49)
  • D
    6% (3)

Why each option

In an IPv6 address, the network ID, also known as the network prefix, is conventionally represented by the first 64 bits of the address.

A32

32 bits is the total length of an IPv4 address, not the network ID portion of an IPv6 address.

B48

While a /48 prefix is common for enterprise global routing prefixes, the standard network ID for a specific subnet in IPv6 is 64 bits.

C64Correct

IPv6 addresses are 128 bits in length, and by standard convention (RFC 4291), the first 64 bits are designated as the network prefix, which uniquely identifies the network segment.

D128

128 bits represents the entire IPv6 address, encompassing both the network prefix and the interface identifier, not solely the network ID.

Concept tested: IPv6 address structure and network prefix length

Source: https://learn.microsoft.com/en-us/windows-server/networking/technologies/ipv6/ipv6-overview

Topics

#IPv6 addressing#IPv6 network ID

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