200-150 · Question #67
Which IPv6 address is the equivalent of the IPv4 interface loopback address 127.0.0.1?
The correct answer is A. ::1. The IPv6 loopback address is ::1, which is the direct equivalent of IPv4's 127.0.0.1. It is always assigned to the loopback interface and never routed externally.
Question
Which IPv6 address is the equivalent of the IPv4 interface loopback address 127.0.0.1?
Options
- A::1
- B::
- C2000::/3
- D0::/10
How the community answered
(41 responses)- A93% (38)
- B5% (2)
- C2% (1)
Why each option
The IPv6 loopback address is ::1, which is the direct equivalent of IPv4's 127.0.0.1. It is always assigned to the loopback interface and never routed externally.
::1 is the IPv6 loopback address, defined in RFC 4291 as the 128-bit address 0:0:0:0:0:0:0:1 (compressed to ::1). Like IPv4's 127.0.0.1, it refers to the local device itself and packets sent to it never leave the host stack. It is used to test the local TCP/IP implementation.
:: (all zeros) is the unspecified address in IPv6, equivalent to IPv4's 0.0.0.0, used to indicate the absence of an address - not the loopback.
2000::/3 is the global unicast address range assigned to publicly routable IPv6 addresses and has no loopback function.
0::/10 is not a defined or standardized IPv6 address range with any loopback function under RFC 4291.
Concept tested: IPv6 loopback address identification
Source: https://www.rfc-editor.org/rfc/rfc4291#section-2.5.3
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