Identify the network portion in the IPv6 address 2001:db8:1:2:0:0:0:1/64.

In the IPv6 address 2001:db8:1:2:0:0:0:1/64, the notation "/64" indicates that the first 64 bits of the address represent the network prefix. To break down the address, it consists of eight groups of four hexadecimal digits. Each group is 16 bits long, so the first four groups amount to 64 bits in total.

The first four groups include 2001, db8, 1, and 2. Therefore, when identifying the network portion, one looks at these initial groups, which collectively define the network. The address up to the fourth group (2001:db8:1:2) delineates the network segment that can be used for routing and addressing devices within that network.

In contrast, the remaining groups (the last four: 0:0:0:1) are part of the interface identifier, which can vary for individual devices. This distinction clarifies why the first four groups represent the network portion, as they identify the broader network environment rather than specific device identifiers. Thus, option A accurately captures the network portion of the given IPv6 address.