Route IPv6 through WireGuard VPN via radvd and static gateway

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

1 files changed, 5 insertions, 6 deletions

diff --git a/roles/gateway/templates/gateway-apply-rules.sh.j2 b/roles/gateway/templates/gateway-apply-rules.sh.j2
index 0ce9f740..daddb180 100644
--- a/roles/gateway/templates/gateway-apply-rules.sh.j2
+++ b/roles/gateway/templates/gateway-apply-rules.sh.j2
@@ -27,8 +27,8 @@ clear_rules() {
     iptables -D OUTPUT -o "$GATEWAY_INTERFACE" -j ACCEPT 2>/dev/null || true
     if [ -n "$GATEWAY_SUBNET_V6" ]; then
         ip6tables -F FORWARD 2>/dev/null || true
-        ip6tables -t nat -D POSTROUTING -s "$GATEWAY_SUBNET_V6" -o wg+ -j MASQUERADE 2>/dev/null || true
-        ip6tables -t nat -D POSTROUTING -s "$GATEWAY_SUBNET_V6" -o "$GATEWAY_INTERFACE" -j MASQUERADE 2>/dev/null || true
+        ip6tables -t nat -D POSTROUTING -o wg+ -j MASQUERADE 2>/dev/null || true
+        ip6tables -t nat -D POSTROUTING -o "$GATEWAY_INTERFACE" -j MASQUERADE 2>/dev/null || true
         ip6tables -D OUTPUT -o wg+ -j ACCEPT 2>/dev/null || true
         ip6tables -D OUTPUT -o "$GATEWAY_INTERFACE" -j ACCEPT 2>/dev/null || true
     fi
@@ -45,7 +45,7 @@ apply_vpn_mode() {
         ip6tables -t nat -A POSTROUTING -o wg+ -j MASQUERADE
         ip6tables -A OUTPUT -o wg+ -j ACCEPT
         ip6tables -A FORWARD -i "$GATEWAY_INTERFACE" -o wg+ -j ACCEPT
-        ip6tables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
+        ip6tables -A FORWARD -i wg+ -o "$GATEWAY_INTERFACE" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
     fi
     log_message "VPN mode rules applied - traffic routed through VPN"
 }
@@ -57,10 +57,9 @@ apply_direct_rules() {
     iptables -A FORWARD -s "$GATEWAY_SUBNET_V4" -o "$GATEWAY_INTERFACE" -j ACCEPT
     iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
     if [ -n "$GATEWAY_SUBNET_V6" ]; then
-        # No MASQUERADE for IPv6: LAN devices have public SLAAC addresses, native routing applies
+        ip6tables -t nat -A POSTROUTING -o "$GATEWAY_INTERFACE" -j MASQUERADE
         ip6tables -A OUTPUT -o "$GATEWAY_INTERFACE" -j ACCEPT
-        ip6tables -A FORWARD -i "$GATEWAY_INTERFACE" -o "$GATEWAY_INTERFACE" -j ACCEPT
-        ip6tables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
+        ip6tables -A FORWARD -i "$GATEWAY_INTERFACE" -o "$GATEWAY_INTERFACE" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
     fi
     log_message "Direct mode rules applied - normal routing active"
 }