Given this IP address 2001::1a3:f1a:308:833, choose the interface ID of it.

It's an IPv6 address. It is 128 bits long, with the last 64 bits representing the interface ID, which identifies the specific computer. Because there are eight groups of hex numbers, the four groups on the right are the interface ID. Any leading zeros in an IPv6 address can be ignored, and the:: can be used once in an address to replace consecutive groups of all zeros, therefore, the given ID's full form would be 2001:0000:0000:0000:01a3:0f1a:0308:0833. As a result, the interface ID is 1a3:f1a:308:833. The network is identified by the first three sections, while the subnet is identified by the fourth. In this example, the site prefix is 2001:0:0, and the subnet ID is 0. IPv6 addresses, unlike IPv4 addresses, do not require a subnet mask.