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Co-Authored-By: Claude.ai
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Root cause: Pi, the ISP router (FritzBox), and LAN clients share the same
L2 segment. When Pi forwards a client's IPv6 packet to an external GUA
destination, the Linux kernel detects that the ISP router is a "better"
next-hop on the same link and sends an ICMPv6 Redirect (type 137) to the
client. The client obeys the redirect and sends its first SYN to the ISP
router directly — Pi never forwards the original packet. The ISP router
applies per-device content filtering to the unmasqueraded client GUA and
issues a RST. This produced the symptom of the first IPv6 request failing
with "Connection reset by peer" every ~30-60 seconds (matching the FritzBox
RA interval, after which clients re-resolve their default gateway).
Diagnosis method: tcpdump with MAC addresses (-e flag) on Pi's end0 caught
the ICMPv6 Redirect being sent immediately after the first SYN arrived.
Inserting a DROP rule for icmpv6-type redirect at position 1 in ip6tables
OUTPUT confirmed the fix — 0 failures across extended testing.
Fix:
- Drop ICMPv6 Redirect (type 137) in ip6tables OUTPUT as the first rule,
before the ACCEPT rule, in both direct and VPN modes
- Flush ip6tables OUTPUT chain on clear_rules() instead of per-rule -D
deletion, which was fragile and left stale rules accumulating across
mode switches (previously caused duplicate/conflicting OUTPUT rules)
- Flush ip6tables nat POSTROUTING table instead of per-rule -D deletion
for the same reason
Also documents the ICMPv6 Redirect issue and IPv6 masquerade rationale
in roles/gateway/README.md for future reference.
Co-Authored-By: Claude Sonnet 4.6 <[email protected]>
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Add radvd to gateway role to advertise Pi as high-preference IPv6
default router using the stable ULA prefix (fd1e:.../64). With
FritzBox also sending RAs, devices end up with ECMP between Pi and
FritzBox. To solve this, add network_ipv6_gateway (Pi's link-local)
as a static route with metric 100 to all managed hosts — beats RA
metric 425, ensuring all IPv6 default traffic goes through Pi.
Fix IPv6 MASQUERADE in gateway-apply-rules:
- Direct mode: add MASQUERADE on end0 (LAN devices use ULA source
addresses not known to FritzBox, so Pi must NAT them)
- FORWARD rules: restrict to RELATED,ESTABLISHED only — previously
the broad ACCEPT rule passed un-NAT'd packets alongside masqueraded
copies, causing duplicate SYNs, conntrack corruption, and RSTs
- MASQUERADE/clear rules: match by interface not by source subnet
(devices may use any source address, not just the ULA prefix)
- VPN mode return traffic: explicitly restrict to wg+→end0 direction
Add network_ipv6_gateway var (optional) to network role NM templates
(ethernet, wifi, bridge) — injects a static IPv6 default route at
metric 100 when set. Add rpi5 static route to FritzBox link-local so
Pi keeps IPv6 after FritzBox RA is disabled.
Force SSH to IPv4 for *.local hosts (AddressFamily inet) — prevents
Ansible from hanging on mDNS returning multiple IPv6 addresses.
Update gateway and pihole READMEs with two-step IPv6 setup process.
Co-Authored-By: Claude.ai
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This reverts commit fdd0b5b58f0ebd39ad05e2dcb17faa6603145f97.
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As the role now functions as a gateway and not just a wireguard gateway
it's better name for clarity
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