Improve the textual representation of IPv4-mapped IPv6 addresses

@opavlyuk

BPO	43633
Nosy	@opavlyuk, @maxmouchet
PRs	gh-87799: Improve the textual representation of IPv4-mapped IPv6 addresses #29345

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-03-26.17:34:40.530>
labels = ['type-feature', 'library']
title = 'Improve the textual representation of IPv4-mapped IPv6 addresses'
updated_at = <Date 2021-11-01.12:05:04.773>
user = 'https://github.com/maxmouchet'

bugs.python.org fields:

activity = <Date 2021-11-01.12:05:04.773>
actor = 'opavlyuk'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-03-26.17:34:40.530>
creator = 'maxmouchet'
dependencies = []
files = []
hgrepos = []
issue_num = 43633
keywords = ['patch']
message_count = 2.0
messages = ['389556', '405434']
nosy_count = 2.0
nosy_names = ['opavlyuk', 'maxmouchet']
pr_nums = ['29345']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue43633'
versions = []

Linked PRs

Python supports IPv4-mapped IPv6 addresses as defined by RFC 4038:
"the IPv6 address ::FFFF:x.y.z.w represents the IPv4 address x.y.z.w.”

The current behavior is as follows:

   from ipaddress import ip_address
   addr = ip_address('::ffff:8.8.4.4') # IPv6Address('::ffff:808:404')
   addr.ipv4_mapped # IPv4Address('8.8.4.4')

Note that the textual representation of the IPv6Address is *not* in IPv4-mapped format.
It prints ::ffff:808:404 instead of ::ffff:8.8.4.4.
This is technically correct, but it’s somewhat frustrating as it makes it harder to read IPv4s embedded in IPv6 addresses.

My proposal would be to check, in __str__, if an IPv6 is an IPv4-mapped, and to return the appropriate representation :

   from ipaddress import ip_address
   addr = ip_address('::ffff:8.8.4.4')

   # Current behavior
   str(addr)  # '::ffff:808:404'
   repr(addr) # IPv6Address('::ffff:808:404')

   # Proposed behavior
   str(addr)  # '::ffff:8.8.4.4'
   repr(addr) # IPv6Address('::ffff:8.8.4.4')

A few data points:

Julia prints ::ffff:808:404 (current behavior)
C (glibc) and ClickHouse prints ::ffff:8.8.4.4 (proposed behavior)

@maxmouchet, thank you for creating the issue.
For me it makes sense, and RFC 4291 calls such IPv6 text representation approach as "more convenient".

I'll try to fix this, if you don't mind.
P.S.: Sorry for providing PR before I asked.

gh-87799: Improve the textual representation of IPv4-mapped IPv6 addr…

Done by #29345

Are there any tests for the reverse_pointer method? I'm seeing strange results with the new behavior:

IP Address: ::FFFF:192.168.1.35

Results in a reverse_pointer of:

5.3...1...8.6.1...2.9.1.f.f.f.f.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa

instead of the old:

3.2.1.0.8.a.0.c.f.f.f.f.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa

I'm not sure which one is more valid or if a pointer record is even relevant in the context of mapped addresses. The original way seems more correct to me if nothing for the fact that there are strange extra dots in the new output.

(I'll create a new issue for this since this one is closed)

gh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped addresses (

pythongh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped ad…

[3.13] gh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped a…

pythongh-87799: Improve the textual representation of IPv4-mapped IPv…

[3.11] gh-87799: Improve the textual representation of IPv4-mapped IP…

[3.12] gh-87799: Improve the textual representation of IPv4-mapped IP…

[3.9] gh-87799: Improve the textual representation of IPv4-mapped IPv…

pythongh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped ad…

[3.10] gh-87799: Improve the textual representation of IPv4-mapped IP…

pythongh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped ad…

[3.10] gh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped a…

[3.11] gh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped a…

[3.12] gh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped a…

[3.9] gh-123409: fix `IPv6Address.reverse_pointer` for IPv4-mapped ad…

I'd like to express my concern that this change got backported to all these patch releases of Python. Surely the feature is not so important that everyone needs to get it immediately? Compared to the tradeoff that this is supposed to be bugfixes-only?

As I'm rushing to apply the latest security release, I see that the patch release also changed our code that produces IPv6 addresses to now produce ::ffff:7.8.9.10 instead of ::ffff:708:90a.

Navigation Menu

Repository navigation

Improve the textual representation of IPv4-mapped IPv6 addresses #87799

Linked PRs

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Improve the textual representation of IPv4-mapped IPv6 addresses #87799

Description

Linked PRs

Activity

maxmouchet commented on Mar 26, 2021

opavlyuk commented on Nov 1, 2021

asvetlov commented on Jul 31, 2023

kellyjonbrazil commented on Aug 1, 2024

oprypin commented on Jun 4, 2025

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions