IPv6 address rules: Which combination of statements about IPv6 addressing is correct?

Introduction / Context:
IPv6 textual representation includes several rules that reduce address length while preserving unambiguous interpretation. Knowing which statements are valid ensures accurate configuration and troubleshooting.

Given Data / Assumptions:

• (1) Leading zeros are required.
• (2) Two colons (::) are used to represent successive hexadecimal fields of zeros.
• (3) Two colons (::) are used to separate fields.
• (4) A single interface will often have multiple IPv6 addresses of different types.

Concept / Approach:

Correct rules: Leading zeros are optional, not required. Double-colon (::) denotes one contiguous run of zero 16-bit blocks and may appear only once in an address. Field separation uses single colons. Interfaces typically hold multiple addresses (link-local, global unicast, possibly unique-local, and temporary/privacy addresses).

Step-by-Step Solution:

Verification / Alternative check:

Examples: 2001:db8:0:0:0:0:0:1 can be 2001:db8::1; 2001:db8:1:0:0:0:0:abcd becomes 2001:db8:1::abcd. Devices show both link-local and global unicast on the same interface with show commands.

Why Other Options Are Wrong:

Any choice including (1) or (3) conflicts with IPv6 textual rules.

Common Pitfalls:

Using :: more than once; forgetting that :: can represent different counts of zeros depending on the rest of the address; assuming each interface has only one address as in traditional IPv4.

Final Answer:

2 and 4