Windows client tries to connect to Pangolin client tunnel port over IPv6 on an IPv4-only network

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
56/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
go, networking
Domain
desktop, networking

Research direction

Start by tracing the Windows client’s DNS resolution and UDP hole-punch setup, using the log’s udp4 write failure to locate the relevant code and tests. Check how resolved A and AAAA records are selected for the active network family. Done means the IPv4-only client uses an IPv4 address for the tunnel connection; add or update coverage for dual-stack DNS results.

Written by the indexing model from the issue text.

Description

Describe the Bug

The clients fails to connect to the self-hosted pangolin server on an IPv4 only network, likely because the first record returned is the AAAA record. The Pangolin server is running dual-stack. The connection works from other dual-stack networks (IPv6 only untested, but does not seem relevant here as that is the resolved address). both A and AAAA records exist and resolve:
mxtoolbox com pangolin domain resolve result

The client does seem to be aware that it is running IPv4 only (udp4) but should only adhere to the A record in that case.

The relevant lines from the client log:
2026-11-12 12:15:09.000 [INFO] Starting hole punch for 1 exit nodes
2026-11-12 12:15:09.000 [WARN] Failed to send initial hole punch to pangolin.my.domain: failed to write to UDP: write udp4 0.0.0.0:49388->[<PangolinIPv6IP>]:21820: address <PangolinIPv6IP>: non-IPv4 address

Full client log file from a connection attempt:
pangolin-log-2026-11-12T121549-redacted.txt

Environment
  • OS Type & Version: Windows 11
  • Pangolin Version: 1.26.0
  • Edition (Community or Enterprise): Enterprise
  • Gerbil Version: 1.6.0
  • Traefik Version: 3.7.18
  • Newt Version: 1.19.1
  • Client Version: 0.16.0
To Reproduce

Install client on a Windows 11 machine on an IPv4-only network (no v6 NAT solutions in place).
Connect to a dual stack server where the first resolved record is the AAAA record.

AI Disclosure

No AI used in writing this bug report.

Expected Behavior

Client identifies the type of network it is on (IPv4, IPv6 or dual-stack) and resolves the correct DNS record type for it's network type.

Dominant language
Go
Stars
26
Forks
10
Avg merge
5h 49m
Merged PRs (30d)
12

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