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Networking Fundamentals · Intermediate

Subnet ID

The bits of an IPv6 address between the global routing prefix and the 64-bit interface ID, used to number subnets within a site.

Definition

With a /48 global routing prefix, the 16-bit subnet ID occupies the fourth hextet, allowing 65,536 /64 subnets. Administrators often encode VLAN numbers or locations in the subnet ID for readability.

Example

In 2001:db8:acad:0010::/64, the subnet ID is 0010, perhaps matching VLAN 10.

Exam tip

IPv6 subnetting usually means incrementing the fourth hextet; no host-count math is needed.

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