How many bits represent network id in a IPv6 address?

Question:
How many bits represent network id in a IPv6 address?

• 32
• 48
• 64
• 128

Explanation: Each ISP receives a /32 and provides a /48 for each site-> every ISP can provide 2^(48-32) = 65,536 site addresses (note: each network organized by a single entity is often called a site).

Each site provides /64 for each LAN -> each site can provide 2^(64-48) = 65,536 LAN addresses for use in their private networks.
So each LAN can provide 2⁶⁴ interface addresses for hosts.

-> Global routing information is identified within the first 64-bit prefix.

Now let’s see an example of IPv6 prefix: 2001:0A3C:5437:ABCD::/64:

In this example, the RIR has been assigned a 12-bit prefix. The ISP has been assigned a 32-bit prefix and the site is assigned a 48-bit site ID. The next 16-bit is the subnet field and it can allow 2¹⁶, or 65536 subnets. This number is redundant for largest corporations on the world!

The 64-bit left (which is not shown the above example) is the Interface ID or host part and it is much more bigger: 64 bits or 2⁶⁴ hosts per subnet! For example, from the prefix 2001:0A3C:5437:ABCD::/64 an administrator can assign an IPv6 address 2001:0A3C:5437:ABCD:218:34EF:AD34:98D to a host.

Exam with this question: CCNA v3.0 (200-125) Study Guide – Exam Dumps