101 · Question #636
In IPv4 the loopback IP is 127.0.0.1. or IPv6, what is the loopback address?
The correct answer is D. : : 1. The IPv6 loopback address is ::1, the compressed form of the all-zeros address with a final bit of 1, analogous to 127.0.0.1 in IPv4.
Question
In IPv4 the loopback IP is 127.0.0.1. or IPv6, what is the loopback address?
Options
- AFEBO::1
- BFF8Q 0.0 : :1
- C2001:: 127 : : 1
- D: : 1
How the community answered
(26 responses)- A4% (1)
- B4% (1)
- D92% (24)
Why each option
The IPv6 loopback address is ::1, the compressed form of the all-zeros address with a final bit of 1, analogous to 127.0.0.1 in IPv4.
FE80::1 is a link-local unicast address prefix used for on-segment communication, not the loopback address.
FF80:0.0::1 is not a valid or recognized IPv6 address and does not correspond to any defined address type.
2001::127::1 is syntactically invalid in IPv6 because only one double-colon (::) is permitted per address.
::1 is the standard IPv6 loopback address as defined in RFC 4291. The double-colon notation compresses consecutive all-zero 16-bit groups, so ::1 expands to 0000:0000:0000:0000:0000:0000:0000:0001. This address is used by a host to send packets to itself, just like 127.0.0.1 in IPv4.
Concept tested: IPv6 loopback address notation and value
Source: https://www.rfc-editor.org/rfc/rfc4291#section-2.5.3
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