In IPv6 addressing, what does the "::" notation represent?

In IPv6 addressing, what does the "::" notation represent?

• A. Consecutive zero blocks
• B. A single zero within a block
• C. The end of the address
• D. A placeholder for an IPv4-mapped address

Answer: (A)

The double colon is a shorthand for a run of consecutive zero 16‑bit blocks in an IPv6 address. It compresses one or more adjacent 0000 blocks to make the address shorter. It can appear only once in an address to avoid ambiguity, and when expanding, it fills in just enough zeros so the total number of 16‑bit blocks reaches eight. For example, 2001:0db8:0000:0000:0000:ff00:0042:8329 becomes 2001:db8::ff00:42:8329, with the :: standing in for the three zero blocks. If the zeros are at the end, 2001:db8:0:0:0:0:2:1 becomes 2001:db8::2:1. If the address is all zeros, it can be written as ::. Note: :: is a mechanism for zero compression, not a placeholder for IPv4-mapped addresses, which use a different form like ::ffff:IPv4-address.

The double colon is a shorthand for a run of consecutive zero 16‑bit blocks in an IPv6 address. It compresses one or more adjacent 0000 blocks to make the address shorter. It can appear only once in an address to avoid ambiguity, and when expanding, it fills in just enough zeros so the total number of 16‑bit blocks reaches eight.

For example, 2001:0db8:0000:0000:0000:ff00:0042:8329 becomes 2001:db8::ff00:42:8329, with the :: standing in for the three zero blocks. If the zeros are at the end, 2001:db8:0:0:0:0:2:1 becomes 2001:db8::2:1. If the address is all zeros, it can be written as ::.

Note: :: is a mechanism for zero compression, not a placeholder for IPv4-mapped addresses, which use a different form like ::ffff:IPv4-address.