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GeezerVison is showing github.com — gh-151749: Add 5f00::/16 (RFC 9602) and 100:0:0:1::/64 (RFC 9780) to ipaddress IPv6 private networks by tonghuaroot · Pull Request #151764 · python/cpython

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@tonghuaroot

@tonghuaroot tonghuaroot commented Jun 20, 2026 •
edited by bedevere-app Bot
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Add the 5f00::/16 (RFC 9602) and 100:0:0:1::/64 (RFC 9780) special-purpose IPv6 ranges to ipaddress's _private_networks so is_global/is_private match the IANA registry.

Fixes #151749

Problem

Both ranges are listed in the IANA IPv6 Special-Purpose Address Registry with Globally Reachable = False, but ipaddress currently reports them as globally reachable:

  • 5f00::/16 — SRv6 SIDs, defined in RFC 9602 (Globally Reachable: False).
  • 100:0:0:1::/64 — Dummy IPv6 Prefix, defined in RFC 9780 (Globally Reachable: False). Note this block is disjoint from the already-listed 100::/64 (RFC 6666 Discard-Only), so it is not currently covered.

Before this change IPv6Address.is_global returns True (and is_private returns False) for addresses in both blocks, which is incorrect.

Fix

Adds the two networks to _IPv6Constants._private_networks, alongside the existing not-globally-reachable IPv6 entries. This follows the precedent set by CVE-2024-4032 / gh-113171 and gh-124217 (3fff::/20, RFC 9637), which added sibling ranges to these same tables.

Scope: This PR is intentionally limited to _private_networks. It does not touch _private_networks_exceptions; the related 2001:1::3/128 (RFC 9665) exception is handled separately in #151050 and is deliberately left unchanged here.

Behaviour (stock vs. patched)

Address stock is_global patched is_global patched is_private
5f00:: True False True
5f00::1 True False True
5f00:ffff:ffff:ffff:ffff:ffff:ffff:ffff True False True
100:0:0:1:: True False True
100:0:0:1:ffff:ffff:ffff:ffff True False True
5eff:ffff:ffff:ffff:ffff:ffff:ffff:ffff (adjacent below) True True False
5f01:: (adjacent above) True True False
100:0:0:2:: (adjacent) True True False

Addresses immediately adjacent to each new block are unchanged. A regression test covering both the changed and adjacent addresses is added to testReservedIpv6, and a Misc/NEWS.d entry is included.

  • Issue: ipaddress: Two more IPv6 ranges (RFC 9602, 9780) missing from _private_networks #151749

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@tonghuaroot
pythongh-151749: Add 5f00::/16 (RFC 9602) and 100:0:0:1::/64 (RFC 978…
928525f 
…0) to ipaddress IPv6 private networks
@bedevere-app bedevere-app Bot added the awaiting review label Jun 20, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Jun 20, 2026
ipaddress: Two more IPv6 ranges (RFC 9602, 9780) missing from _private_networks #151749
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@tonghuaroot
pythongh-151749: Match surrounding comment and test style
0e67dce
aisk
aisk approved these changes Jun 20, 2026
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@bedevere-app bedevere-app Bot added awaiting core review and removed awaiting review labels Jun 20, 2026
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github-actions Bot commented Sep 23, 2026

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This PR is stale because it has been open for 90 days with no activity.
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@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label Sep 23, 2026
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@tonghuaroot @aisk
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