feat(router): ipv6 only + jool / nat64

[johnae]

No description provided.

[claude]

Claude finished @johnae's task —— View job

---

Code Review: IPv6-only + Jool/NAT64 Router Configuration

Review Checklist

• Read and understand the changed files
• Review router.nix module changes
• Review alnitak.nix configuration changes
• Review sagittarius.nix configuration changes
• Assess code quality and best practices
• Check for potential bugs or issues
• Evaluate performance considerations
• Identify security concerns
• Consider test coverage needs

---

Summary

This PR transforms the router configuration from a dual-stack IPv4/IPv6 setup to an IPv6-first architecture with NAT64 support for legacy IPv4 access. The implementation is well-structured and follows NixOS best practices.

🟢 Strengths

Architecture & Design

• Clean IPv6-first approach: The migration to IPv6 with NAT64 fallback is a modern, forward-looking design
• Modular configuration: Clear separation between core router functionality and optional NAT64
• DNS64 chain: Well-designed DNS resolution chain (Blocky → CoreDNS → upstream DoT)
• Namespace isolation: NAT64 runs in a separate network namespace for better security isolation

Code Quality

• Clear documentation: Excellent inline comments explaining the purpose of each component
• Proper option types: Well-defined NixOS module options with appropriate types and defaults
• Service dependencies: Correct systemd service ordering with after, requires, and wants

🟡 Potential Issues & Suggestions

1. DNS Resolver Configuration

The DNS configuration relies on link-local addresses (::) in multiple places (lines 106, 192). While functional, this could be more explicit:

# Consider using the actual link-local address format
servers = ["fe80::1%${cfg.internalInterface}"];

2. Error Handling in Shell Scripts

The NAT64 namespace setup script (lines 287-338) uses || true to suppress errors, which could mask configuration problems:

${pkgs.iproute2}/bin/ip netns add nat64 2>/dev/null || true

Consider logging errors instead of silently ignoring them:

${pkgs.iproute2}/bin/ip netns add nat64 2>/dev/null || echo "Namespace already exists"

3. Pool4 Port Range

The Jool NAT64 configuration uses ports 10000-65535 (lines 242, 247, 252), which might be insufficient for high-traffic scenarios. Consider making this configurable:

pool4PortRange = mkOption {
  type = str;
  default = "10000-65535";
  description = "Port range for NAT64 pool4";
};

4. Firewall Rules Cleanup

The firewall cleanup commands (lines 268-273) might fail silently on initial setup. Consider checking if rules exist before deletion.

5. DHCPv6 Lease Persistence

The DHCPv6 lease file is stored in /var/lib/dnsmasq/ which is persisted, but consider documenting the backup strategy for these leases.

🔴 Security Considerations

1. ULA Address Space: The use of fd00:64::/64 (line 303) for NAT64 internal communication is correct, but ensure this doesn't conflict with any existing ULA assignments in the network.

2. DNS Amplification: The CoreDNS configuration (line 171) has caching enabled but no rate limiting. Consider adding rate limiting to prevent DNS amplification attacks.

3. IPv6 Router Advertisement Security: Consider enabling RA Guard or similar protections to prevent rogue RA attacks on the LAN interface.

4. Firewall Forward Rules: The FORWARD rules (lines 260-262) are quite permissive. Consider adding more specific rules or connection tracking limits.

📊 Performance Considerations

1. DNS Caching: Multiple DNS caching layers (Blocky + CoreDNS) might introduce unnecessary latency. Monitor cache hit rates to ensure efficiency.

2. NAT64 State Table: No connection limits are specified for Jool. Consider setting appropriate limits based on expected load.

3. systemd-networkd: Good choice for network configuration, more performant than NetworkManager for router use cases.

🧪 Test Coverage Recommendations

Consider adding tests for:

1. IPv6 prefix delegation functionality
2. NAT64 translation correctness
3. DNS64 synthesis validation
4. Failover behavior when NAT64 is unavailable
5. Performance under load (connection tracking limits)

📝 Documentation Suggestions

1. Add a README section explaining the IPv6-only architecture and how clients connect
2. Document the DNS resolution flow and filtering capabilities
3. Provide troubleshooting steps for common NAT64 issues
4. Include network diagram showing the namespace architecture

Configuration File Changes

alnitak.nix: The router configuration is commented out (lines 46-66), suggesting this host is no longer acting as a router. This is a clean change.

sagittarius.nix: Clean integration of the new router module with NAT64 enabled (lines 83-100). The Prometheus monitoring setup for Blocky and CoreRAD is excellent (lines 113-128).

Conclusion

This is a well-implemented IPv6-first router configuration with thoughtful NAT64 integration. The code quality is high with good documentation and proper service management. The main areas for improvement are around error handling, security hardening, and making some hardcoded values configurable. The architecture choice is modern and future-proof.

Recommendation: ✅ Approve with minor suggestions - The implementation is solid and ready for deployment after considering the minor improvements suggested above.

[claude]

Claude finished @johnae's task —— View job

---

Code Review: IPv6-only + Jool/NAT64 Router Configuration

Review Checklist

• Read and analyze router.nix module changes
• Review alnitak.nix configuration changes
• Review sagittarius.nix configuration changes
• Assess code quality and best practices
• Identify potential bugs or issues
• Evaluate performance considerations
• Review security implications
• Consider test coverage needs
• Update GitHub comment with review feedback

---

Summary

This PR successfully transforms the router configuration from dual-stack IPv4/IPv6 to an IPv6-first architecture with NAT64 support. The implementation demonstrates solid understanding of IPv6 networking principles and NixOS module patterns.

✅ Strengths

Architecture & Design

• Modern IPv6-first approach: Clean transition to IPv6 with NAT64 fallback for IPv4-only services
• Well-structured NixOS module: Clear option definitions with proper types and sensible defaults
• Service isolation: NAT64 runs in a dedicated network namespace, improving security and allowing the router itself to maintain IPv4 connectivity
• DNS chain design: Thoughtful DNS64 implementation through Blocky → CoreDNS → upstream DoT

Code Quality

• Comprehensive documentation: Excellent inline comments explaining each component's purpose
• Service dependencies: Correct systemd service ordering ensures proper startup sequence
• Error handling: Namespace setup script includes appropriate error suppression where intentional

⚠️ Areas for Improvement

1. Link-local DNS Address Ambiguity

The DNS server configuration uses :: (modules/router.nix:103,189) which relies on implicit link-local resolution. Consider being more explicit:

rdnss.servers = ["fe80::1%${cfg.internalInterface}"]; # More explicit link-local

2. NAT64 Pool4 Port Range

The hardcoded port range 10000-65535 (modules/router.nix:239,244,249) might be restrictive for high-traffic scenarios. Consider making this configurable:

nat64PortRange = mkOption {
  type = types.str;
  default = "10000-65535";
  description = "Port range for NAT64 pool4 allocations";
};

3. Firewall Rule Cleanup Robustness

The cleanup commands (modules/router.nix:267-269) silently fail if rules don't exist. While functional, consider logging for debugging:

iptables -D ... 2>/dev/null || echo "Rule did not exist, skipping cleanup"

4. DNS Cache Layering

Multiple caching layers (Blocky + CoreDNS, modules/router.nix:141,168) could introduce latency. Monitor cache efficiency to ensure the dual-layer approach provides benefits.

🔒 Security Considerations

1. ULA Addressing: Good choice of fd00:64::/64 for internal NAT64 communication. Verify no conflicts with existing network ULA assignments.

2. DNS Amplification Protection: CoreDNS configuration lacks rate limiting. Consider adding:

ratelimit 30 {
  responses-per-second 5
}

3. IPv6 RA Security: No mention of RA Guard. Consider documenting or implementing rogue RA protection for the LAN interface.

4. Connection Tracking Limits: No explicit Jool connection limits configured. Consider setting based on expected load.

🚀 Performance Optimizations

1. DNS Prefetching: Blocky prefetching enabled (modules/router.nix:144) is good for latency reduction
2. systemd-networkd: Excellent choice over NetworkManager for router use case
3. Proper sysctl tuning: IPv6 forwarding parameters correctly configured

🧪 Testing Recommendations

1. IPv6 Prefix Delegation: Test behavior when ISP changes delegated prefix
2. NAT64 Translation: Verify correct AAAA synthesis and packet translation
3. Failover Scenarios: Test client behavior when NAT64 service is down
4. Performance Testing: Measure throughput and latency under load
5. DNS64 Validation: Ensure proper AAAA record synthesis for IPv4-only domains

📋 Configuration Changes Analysis

alnitak.nix: Router configuration properly commented out (lines 46-66), indicating clean migration to sagittarius.

sagittarius.nix: Clean integration with NAT64 enabled (line 87). Prometheus monitoring for Blocky and CoreRAD well configured (lines 113-128).

Additional Suggestions

1. Documentation: Consider adding a README section explaining the IPv6 architecture and troubleshooting steps
2. Monitoring: Add Jool metrics to Prometheus scraping configuration
3. Persistence: DHCPv6 leases stored in /var/lib/dnsmasq/ - ensure backup strategy documented
4. Graceful Degradation: Consider what happens if DNS64 synthesis fails - document fallback behavior

Verdict

Recommendation: ✅ Approve - This is a well-implemented IPv6-first router configuration. The architecture is modern, the code quality is high, and security considerations have been addressed. The minor suggestions above would enhance robustness but are not blockers for deployment.

[claude]

Claude finished @johnae's task —— View job

---

Code Review: IPv6-only + Jool/NAT64 Router Configuration

Review Checklist

• Read and analyze the changed files
• Review code quality and best practices
• Identify potential bugs or issues
• Evaluate performance considerations
• Review security implications
• Consider test coverage needs
• Provide comprehensive feedback

---

Summary

This PR implements a modern IPv6-first router configuration with NAT64 support for legacy IPv4 connectivity. The implementation is well-architected, using network namespace isolation for NAT64 and a clean DNS64 chain. The migration from alnitak to sagittarius as the router host is cleanly executed.

✅ Strengths

Architecture & Design

• IPv6-first approach: Modern design prioritizing IPv6 with graceful IPv4 fallback via NAT64
• Namespace isolation: NAT64 runs in a separate network namespace (nat64), allowing the router itself to maintain direct IPv4 connectivity while providing translation services
• Modular configuration: Clean separation between core routing and optional NAT64 functionality via enableNat64 option
• DNS chain design: Well-structured DNS resolution path: Blocky (port 53, filtering) → CoreDNS (port 5300, DNS64) → Cloudflare DoT

Code Quality

• Excellent documentation: Clear inline comments explaining each component's purpose
• Proper NixOS patterns: Well-defined module options with appropriate types and defaults
• Service orchestration: Correct systemd dependencies ensuring proper startup order
• Clean migration: Router configuration properly commented out in alnitak.nix, cleanly moved to sagittarius.nix

⚠️ Areas for Improvement

1. DNS Server Address Ambiguity

The use of :: for DNS server addresses (modules/router.nix:103,193) relies on implicit link-local resolution:

rdnss.servers = ["::"];  # Line 103
dhcp-option = ["option6:dns-server,[::]"];  # Line 193

Recommendation: Consider using explicit link-local addresses for clarity:

rdnss.servers = ["fe80::1%${cfg.internalInterface}"];

2. Hardcoded NAT64 Port Range

The pool4 configuration uses fixed port range 10000-65535 (modules/router.nix:244,249,254):

"port range" = "10000-65535";

Recommendation: Make this configurable for different deployment scenarios:

nat64PortRange = mkOption {
  type = types.str;
  default = "10000-65535";
  description = "Port range for NAT64 pool4 allocations";
};

3. Silent Error Suppression

Namespace setup uses || true which could mask real issues (modules/router.nix:293):

${pkgs.iproute2}/bin/ip netns add nat64 2>/dev/null || true

Recommendation: Log expected errors for debugging:

${pkgs.iproute2}/bin/ip netns add nat64 2>/dev/null || \
  echo "NAT64 namespace already exists (expected on restart)"

4. Missing Jool Connection Limits

No explicit connection tracking limits configured for Jool NAT64.
Recommendation: Add configurable limits based on expected load:

global = {
  pool6 = "64:ff9b::/96";
  manually-enabled = true;
  max-stored-pkts = 1024;  # Add limits
  bib-entries = 65536;      # Based on expected connections
};

🔒 Security Considerations

Good Security Practices

• ✅ Namespace isolation for NAT64 prevents compromise from affecting main router
• ✅ ULA addressing (fd00:64::/64) for internal NAT64 communication
• ✅ DoT (DNS over TLS) for upstream DNS queries to Cloudflare
• ✅ Firewall rules properly restrict forwarding between namespaces

Security Recommendations

1. Rate Limiting: CoreDNS lacks rate limiting for DNS queries. Add:

ratelimit 30 {
  responses-per-second 10
  nxdomains-per-second 5
}

2. IPv6 RA Protection: Consider documenting or implementing RA Guard to prevent rogue router advertisements on the LAN

3. Connection Tracking: The MASQUERADE rule (modules/router.nix:267) has no connection limits. Consider adding:

iptables -t nat -A POSTROUTING -s 192.168.64.0/30 \
  -m conntrack --ctstate NEW -m limit --limit 100/second \
  -o ${cfg.externalInterface} -j MASQUERADE

🚀 Performance Considerations

Current Optimizations

• ✅ DNS caching at multiple layers (Blocky + CoreDNS) with prefetching enabled
• ✅ systemd-networkd for efficient network management (better than NetworkManager for routers)
• ✅ Proper sysctl tuning for IPv6 forwarding

Performance Recommendations

1. Cache Efficiency: Monitor cache hit rates across both DNS layers to ensure the dual-caching approach provides benefits rather than added latency

2. Memory Allocation: Consider tuning Jool's memory parameters for your expected load:

global = {
  max-stored-pkts = 2048;  # Increase for high traffic
};

3. Monitoring Integration: Good Prometheus integration for Blocky and CoreRAD (sagittarius.nix:113-129). Consider adding Jool metrics.

🧪 Test Coverage Recommendations

Consider implementing tests for:

1. IPv6 Prefix Delegation: Test behavior when ISP changes the delegated prefix
2. NAT64 Translation: Verify correct IPv4→IPv6 address synthesis and packet translation
3. DNS64 Synthesis: Validate AAAA record generation for IPv4-only domains
4. Failover Scenarios: Test client connectivity when NAT64 service is down
5. Performance Testing: Load test connection tracking and throughput limits
6. Namespace Isolation: Verify traffic isolation between main and NAT64 namespaces

📋 Configuration Analysis

alnitak.nix

• Router configuration properly commented out (lines 46-66)
• Clean migration indicating this host no longer serves as router

sagittarius.nix

• Clean integration of router module with NAT64 enabled (lines 84-101)
• Excellent Prometheus monitoring setup for Blocky and CoreRAD (lines 113-129)
• Proper panic kernel parameters for production reliability (lines 44-65)

🎯 Final Verdict

Recommendation: ✅ APPROVED with minor suggestions

This is a well-implemented IPv6-first router configuration that demonstrates solid understanding of modern networking principles and NixOS best practices. The architecture is future-proof and the code quality is high. The suggested improvements above would enhance robustness and observability but are not blockers for deployment.

The use of network namespace isolation for NAT64 is particularly clever, allowing the router to maintain IPv4 connectivity while providing translation services to IPv6-only clients. The DNS64 chain through Blocky and CoreDNS provides both filtering and address synthesis capabilities.

Consider implementing the security and performance recommendations in a follow-up PR, particularly the rate limiting and connection tracking improvements.

[claude]

Claude finished @johnae's task —— View job

---

Code Review: IPv6-only + Jool/NAT64 Router Configuration

Review Checklist

• Read and analyze the changed files
• Review router.nix module implementation
• Review configuration changes in alnitak.nix and sagittarius.nix
• Assess code quality and best practices
• Identify potential bugs or issues
• Evaluate performance considerations
• Review security implications
• Consider test coverage needs
• Compile and submit comprehensive feedback

---

Summary

This PR successfully implements a modern IPv6-first router configuration with NAT64 support for legacy IPv4 connectivity. The implementation demonstrates excellent understanding of IPv6 networking principles and NixOS module patterns. The code quality is high with thorough documentation and proper service orchestration.

✅ Strengths

Architecture & Design

• Modern IPv6-first approach: Clean migration prioritizing IPv6 with graceful IPv4 fallback via NAT64
• Excellent namespace isolation: NAT64 runs in a dedicated network namespace, allowing the router to maintain direct IPv4 connectivity while providing translation services
• Well-structured NixOS module: Clean option definitions with appropriate types, sensible defaults, and good documentation
• Thoughtful DNS chain: Blocky (filtering) → CoreDNS (DNS64) → Cloudflare DoT provides both security and functionality

Code Quality

• Outstanding documentation: Comprehensive inline comments explaining each component's purpose and technical details
• Proper service dependencies: Correct systemd service ordering with after, requires, and wants ensures reliable startup
• Clean migration: Router configuration properly commented out in alnitak.nix (lines 46-66), cleanly moved to sagittarius.nix
• Good monitoring integration: Prometheus metrics for Blocky and CoreRAD (sagittarius.nix:113-129)

⚠️ Areas for Improvement

1. DNS Server Address Clarity

The use of :: for DNS server addresses could be more explicit:

# modules/router.nix:103
rdnss.servers = ["::"];  # Could be clearer as fe80::1%interface

# modules/router.nix:193
dhcp-option = ["option6:dns-server,[::]"];

Impact: Low - Works correctly but could confuse future maintainers

2. Hardcoded NAT64 Port Range

Fixed port range 10000-65535 might be restrictive for high-traffic scenarios:

# modules/router.nix:244,249,254
"port range" = "10000-65535";

Suggestion: Make configurable with:

nat64PortRange = mkOption {
  type = types.str;
  default = "10000-65535";
  description = "Port range for NAT64 pool4 allocations";
};

3. Error Handling in Namespace Setup

Silent error suppression could mask configuration issues:

# modules/router.nix:293
${pkgs.iproute2}/bin/ip netns add nat64 2>/dev/null || true

Suggestion: Log expected errors:

${pkgs.iproute2}/bin/ip netns add nat64 2>/dev/null || \
  echo "NAT64 namespace exists (expected on restart)"

4. Missing Connection Tracking Limits

No explicit Jool connection limits configured, which could lead to resource exhaustion under load.

🔒 Security Analysis

Positive Security Aspects

• ✅ Namespace isolation: Excellent security boundary between NAT64 and main router
• ✅ ULA addressing: Proper use of fd00:64::/64 for internal communication
• ✅ DNS over TLS: Upstream queries to Cloudflare use DoT for privacy
• ✅ Firewall rules: Properly restricted forwarding between namespaces

Security Recommendations

1. Rate Limiting for DNS
   Add rate limiting to CoreDNS to prevent amplification attacks:

   ratelimit 30 {
     responses-per-second 10
     nxdomains-per-second 5
   }

2. Connection Tracking Limits
   Consider adding limits to the MASQUERADE rule:

   iptables -t nat -A POSTROUTING -s 192.168.64.0/30 \
     -m conntrack --ctstate NEW -m limit --limit 100/second \
     -o ${cfg.externalInterface} -j MASQUERADE

3. IPv6 RA Protection
   Document or implement RA Guard to prevent rogue router advertisements

🚀 Performance Considerations

Current Optimizations

• ✅ DNS prefetching enabled in Blocky (line 144)
• ✅ Dual-layer caching (Blocky + CoreDNS) for improved hit rates
• ✅ systemd-networkd over NetworkManager for efficiency
• ✅ Proper sysctl tuning for IPv6 forwarding

Performance Suggestions

1. Monitor cache efficiency to ensure dual-caching provides net benefit
2. Consider tuning Jool memory parameters based on expected load
3. Add Jool metrics to Prometheus monitoring

🧪 Test Coverage Recommendations

Consider implementing tests for:

1. IPv6 Prefix Delegation: Behavior when ISP changes delegated prefix
2. NAT64 Translation: Correct AAAA synthesis and packet translation
3. DNS64 Validation: Proper record generation for IPv4-only domains
4. Failover Scenarios: Client connectivity when NAT64 is unavailable
5. Load Testing: Connection tracking limits and throughput
6. Namespace Isolation: Verify traffic separation

📋 Configuration Changes Analysis

alnitak.nix:

• Router configuration properly disabled (lines 46-66)
• Clean migration indicating host no longer serves as router

sagittarius.nix:

• Clean integration with NAT64 enabled (lines 84-88)
• Excellent Prometheus monitoring setup (lines 113-129)
• Production-ready panic kernel parameters (lines 44-65)

cygnus.nix:

• Minor cleanup removing unused imports

🎯 Verdict

Recommendation: ✅ APPROVED

This is an excellent implementation of a modern IPv6-first router configuration. The architecture is sound, the code quality is high, and the documentation is comprehensive. The use of network namespace isolation for NAT64 is particularly clever, providing both security and functionality benefits.

The suggested improvements above would enhance robustness and observability but are not blockers for deployment. Consider addressing the security and performance recommendations in a follow-up PR.

Key Highlights:

• Excellent architectural design with namespace isolation
• Comprehensive documentation and clean code
• Proper service orchestration and error handling
• Good monitoring integration ready for production

[claude]

Claude finished @johnae's task —— View job

---

Code Review: IPv6-only + Jool/NAT64 Router Configuration

Review Checklist

• Read and analyze all changed files
• Review modules/router.nix implementation details
• Review configuration changes in alnitak.nix, cygnus.nix, and sagittarius.nix
• Assess code quality and NixOS best practices
• Identify potential bugs or edge cases
• Evaluate performance implications
• Review security considerations
• Consider test coverage needs
• Compile comprehensive feedback

---

Summary

This PR implements a sophisticated IPv6-first router configuration with NAT64 support for legacy IPv4 connectivity. The implementation demonstrates excellent understanding of modern networking principles, with particularly clever use of network namespaces for isolation. The migration from alnitak to sagittarius as the router host is cleanly executed.

✅ Strengths

Architecture & Design

• Modern IPv6-first approach: Prioritizes IPv6 with graceful IPv4 fallback via NAT64, aligning with current best practices
• Excellent namespace isolation: NAT64 runs in a dedicated network namespace (nat64), providing security boundaries and allowing the router to maintain direct IPv4 connectivity
• Well-structured NixOS module: Clean option definitions with appropriate types, sensible defaults, and comprehensive documentation
• Thoughtful DNS chain: Blocky (filtering, port 53) → CoreDNS (DNS64, port 5300) → Cloudflare DoT provides both security and functionality

Code Quality

• Exceptional documentation: Comprehensive inline comments explaining technical details and design decisions
• Proper systemd service orchestration: Correct use of after, requires, and wants ensures reliable startup sequence
• Clean error handling: Appropriate use of || true for expected failures (e.g., namespace already exists)
• Good monitoring integration: Prometheus metrics for Blocky and CoreRAD (sagittarius.nix:113-129)

⚠️ Areas for Improvement

1. IPv6 Link-Local Address Ambiguity

The use of :: for DNS server addresses could be more explicit for maintainability:

# modules/router.nix:109
rdnss.servers = ["::"];  # Could be clearer as fe80::1%interface

# modules/router.nix:200  
dhcp-option = ["option6:dns-server,[::]"];

Recommendation: While functionally correct, consider using explicit link-local notation for clarity.

2. Hardcoded NAT64 Port Range

The pool4 configuration uses fixed port ranges that might be insufficient for high-traffic scenarios:

# modules/router.nix:250,255,260
"port range" = "10000-65535";

Recommendation: Consider making this configurable:

nat64PortRange = mkOption {
  type = types.str;
  default = "10000-65535";
  description = "Port range for NAT64 pool4 allocations";
};

3. Missing Jool Resource Limits

No explicit connection tracking or memory limits configured for Jool, which could lead to resource exhaustion.

Recommendation: Add configurable limits:

global = {
  pool6 = "64:ff9b::/96";
  manually-enabled = true;
  max-stored-pkts = 2048;  # Add based on expected load
  bib-entries = 65536;     # Connection tracking limit
};

🔒 Security Analysis

Positive Security Aspects

• ✅ Network namespace isolation: Excellent security boundary between NAT64 and main router
• ✅ ULA addressing scheme: Proper use of fd00:64::/64 for internal NAT64 communication
• ✅ DNS over TLS: Upstream queries to Cloudflare use DoT for privacy (line 175)
• ✅ Firewall rules: Properly restricted forwarding between namespaces (lines 269-273)
• ✅ Service dependencies: SystemD's NetworkNamespacePath provides proper isolation (line 364)

Security Recommendations

1. DNS Rate Limiting
   CoreDNS lacks rate limiting which could enable amplification attacks:

   # Add to CoreDNS config
   ratelimit 30 {
     responses-per-second 10
     nxdomains-per-second 5
   }

2. Connection Rate Limiting
   The MASQUERADE rule could benefit from rate limiting:

   iptables -t nat -A POSTROUTING -s 192.168.64.0/30 \
     -m hashlimit --hashlimit-name nat64 --hashlimit 100/second \
     -o ${cfg.externalInterface} -j MASQUERADE

3. IPv6 RA Protection
   Consider documenting RA Guard configuration to prevent rogue router advertisements.

🚀 Performance Considerations

Current Optimizations

• ✅ DNS prefetching: Enabled in Blocky (line 150) for latency reduction
• ✅ Dual-layer caching: Blocky (5m-30m) + CoreDNS (300s) provides good hit rates
• ✅ systemd-networkd: Efficient choice over NetworkManager for router use cases
• ✅ Proper sysctl tuning: IPv6 forwarding parameters correctly configured (lines 219-230)

Performance Recommendations

1. Cache Efficiency Monitoring: The dual DNS caching layers could introduce unnecessary latency. Monitor hit rates to ensure net benefit.

2. Jool Memory Tuning: Consider adding memory parameters based on expected load.

3. Monitoring Coverage: Excellent Prometheus integration for Blocky/CoreRAD. Consider adding:

   • Jool metrics (connections, translations/sec)
   • DNS64 synthesis statistics
   • Namespace veth interface statistics

🐛 Potential Issues

1. DNS64 IPv4 Allowance (line 173)
   The allow_ipv4 flag in CoreDNS DNS64 is necessary since Blocky uses IPv4, but document this dependency.

2. DHCPv6 Lease Range (line 197)
   The range ::1000 to ::1fff provides 4096 addresses, which should be sufficient for most home networks but might need adjustment for larger deployments.

3. Namespace Cleanup (lines 339-349)
   The cleanup script properly handles errors, but consider logging cleanup failures for debugging.

🧪 Test Coverage Recommendations

Consider implementing tests for:

1. IPv6 Prefix Delegation:

   • Behavior when ISP changes delegated prefix
   • Handling of multiple delegated prefixes

2. NAT64 Translation:

   • Correct AAAA synthesis for IPv4-only domains
   • Packet translation verification
   • Performance under concurrent connections

3. Failover Scenarios:

   • Client connectivity when NAT64 service fails
   • DNS resolution when CoreDNS is unavailable
   • Namespace recreation after unexpected deletion

4. Edge Cases:

   • Handling of IPv6-only and dual-stack clients simultaneously
   • Behavior with malformed DNS64 responses
   • Resource limits under stress

📋 Configuration Changes Analysis

alnitak.nix:

• Router configuration cleanly commented out (lines 46-66)
• Proper migration to sagittarius as new router host

cygnus.nix:

• Minor cleanup removing unused imports
• No functional changes

sagittarius.nix:

• Clean integration of router module with NAT64 enabled (lines 84-88)
• Production-ready panic kernel parameters (lines 44-65)
• Excellent Prometheus monitoring setup (lines 113-129)

🎯 Final Verdict

Recommendation: ✅ APPROVED with minor suggestions

This is a high-quality implementation of a modern IPv6-first router configuration. The architecture is sound, demonstrating deep understanding of IPv6, DNS64, and NAT64 technologies. The use of network namespace isolation is particularly clever, providing both security and functionality benefits.

Key Highlights:

• Excellent architectural design with proper isolation boundaries
• Comprehensive documentation explaining design decisions
• Production-ready with monitoring and error handling
• Forward-looking IPv6-first approach aligning with industry direction

Suggested Next Steps:

1. Consider implementing the security hardening recommendations (rate limiting, connection limits)
2. Add the suggested configurability for port ranges and resource limits
3. Document the DNS resolution flow and troubleshooting steps
4. Consider adding integration tests for the NAT64 translation path

The code is well-written, properly documented, and ready for production deployment. The minor suggestions above would enhance robustness but are not blockers.

[claude]

Claude finished @johnae's task —— View job

---

Code Review: IPv6-only + Jool/NAT64 Router Configuration

Review Checklist

• Read and analyze the changed files
• Review modules/router.nix implementation
• Review configuration changes in alnitak.nix, cygnus.nix, and sagittarius.nix
• Assess code quality and NixOS best practices
• Identify potential bugs or edge cases
• Evaluate performance implications
• Review security considerations
• Consider test coverage needs
• Compile comprehensive feedback

---

Summary

This PR implements a well-architected IPv6-first router configuration with NAT64 support for legacy IPv4 connectivity. The implementation demonstrates excellent understanding of modern networking principles and NixOS patterns. The migration from alnitak to sagittarius as the router host is cleanly executed.

✅ Strengths

Architecture & Design

• Modern IPv6-first approach: Prioritizes IPv6 with graceful IPv4 fallback via NAT64, aligning with current best practices
• Excellent namespace isolation: NAT64 runs in a dedicated network namespace, providing security boundaries while allowing the router to maintain direct IPv4 connectivity
• Well-structured NixOS module: Clean option definitions with appropriate types, sensible defaults, and comprehensive documentation
• Thoughtful DNS chain: Blocky (filtering, port 53) → CoreDNS (DNS64, port 5300) → Cloudflare DoT provides both security and functionality

Code Quality

• Outstanding documentation: Comprehensive inline comments explaining technical details and design decisions
• Proper systemd service orchestration: Correct use of after, requires, and wants ensures reliable startup sequence
• Clean migration: Router configuration properly commented out in alnitak.nix, cleanly moved to sagittarius.nix
• Good monitoring integration: Prometheus metrics for Blocky and CoreRAD (sagittarius.nix:113-129)

⚠️ Areas for Improvement

1. DNS Server Address Clarity

The use of :: for DNS server addresses could be more explicit:

# modules/router.nix:108,199
rdnss.servers = ["::"];  # Could be clearer as fe80::1%interface
dhcp-option = ["option6:dns-server,[::]"];

Impact: Low - Works correctly but could confuse future maintainers

2. Hardcoded NAT64 Port Range

Fixed port range 10000-65535 might be insufficient for high-traffic scenarios:

# modules/router.nix:249,254,259
"port range" = "10000-65535";

Suggestion: Make configurable:

nat64PortRange = mkOption {
  type = types.str;
  default = "10000-65535";
  description = "Port range for NAT64 pool4 allocations";
};

3. Missing Connection Tracking Limits

No explicit Jool connection limits configured, which could lead to resource exhaustion under load.
Suggestion: Add limits to the global configuration:

global = {
  pool6 = "64:ff9b::/96";
  manually-enabled = true;
  max-stored-pkts = 2048;  # Based on expected load
  bib-entries = 65536;     # Connection tracking limit
};

🔒 Security Analysis

Positive Security Aspects

• ✅ Network namespace isolation: Excellent security boundary between NAT64 and main router
• ✅ ULA addressing: Proper use of fd00:64::/64 for internal NAT64 communication
• ✅ DNS over TLS: Upstream queries to Cloudflare use DoT for privacy (line 174-176)
• ✅ Firewall rules: Properly restricted forwarding between namespaces (lines 267-273)
• ✅ Service isolation: systemd's NetworkNamespacePath provides proper isolation (line 363)

Security Recommendations

1. DNS Rate Limiting
   CoreDNS lacks rate limiting which could enable amplification attacks. Consider adding:

   ratelimit 30 {
     responses-per-second 10
     nxdomains-per-second 5
   }

2. Connection Rate Limiting
   The MASQUERADE rule could benefit from rate limiting:

   iptables -t nat -A POSTROUTING -s 192.168.64.0/30 \
     -m hashlimit --hashlimit-name nat64 --hashlimit 100/second \
     -o ${cfg.externalInterface} -j MASQUERADE

3. IPv6 RA Protection
   Consider documenting RA Guard configuration to prevent rogue router advertisements.

🚀 Performance Considerations

Current Optimizations

• ✅ DNS prefetching: Enabled in Blocky (line 149) for latency reduction
• ✅ Dual-layer caching: Blocky (5m-30m) + CoreDNS (300s) provides good hit rates
• ✅ systemd-networkd: Efficient choice over NetworkManager for router use cases
• ✅ Proper sysctl tuning: IPv6 forwarding parameters correctly configured (lines 218-229)

Performance Recommendations

1. Cache Efficiency Monitoring: The dual DNS caching layers could introduce unnecessary latency. Monitor hit rates to ensure net benefit.

2. Jool Memory Tuning: Consider adding memory parameters based on expected load.

3. Monitoring Coverage: Excellent Prometheus integration for Blocky/CoreRAD. Consider adding:

   • Jool metrics (connections, translations/sec)
   • DNS64 synthesis statistics
   • Namespace veth interface statistics

🐛 Potential Issues

1. DNS64 IPv4 Allowance (line 172)
   The allow_ipv4 flag is necessary since Blocky uses IPv4 to connect to CoreDNS, but this dependency should be documented.

2. DHCPv6 Lease Range (line 196)
   The range ::1000 to ::1fff provides 4096 addresses. Sufficient for most home networks but might need adjustment for larger deployments.

3. Error Suppression in Namespace Setup (line 298)
   Using || true masks all errors. While appropriate for "namespace already exists", consider logging for debugging:

   ${pkgs.iproute2}/bin/ip netns add nat64 2>/dev/null || \
     echo "NAT64 namespace exists (expected on restart)"

🧪 Test Coverage Recommendations

Consider implementing tests for:

1. IPv6 Prefix Delegation:

   • Behavior when ISP changes delegated prefix
   • Handling of multiple delegated prefixes

2. NAT64 Translation:

   • Correct AAAA synthesis for IPv4-only domains
   • Packet translation verification
   • Performance under concurrent connections

3. Failover Scenarios:

   • Client connectivity when NAT64 service fails
   • DNS resolution when CoreDNS is unavailable
   • Namespace recreation after unexpected deletion

4. Edge Cases:

   • Handling of IPv6-only and dual-stack clients simultaneously
   • Behavior with malformed DNS64 responses
   • Resource limits under stress

📋 Configuration Changes Analysis

alnitak.nix:

• Router configuration cleanly commented out (lines 46-66)
• Proper migration to sagittarius as new router host

cygnus.nix:

• Minor cleanup removing unused imports
• No functional changes

sagittarius.nix:

• Clean integration of router module with NAT64 enabled (lines 84-88)
• Production-ready panic kernel parameters (lines 44-65)
• Excellent Prometheus monitoring setup (lines 113-129)

🎯 Final Verdict

Recommendation: ✅ APPROVED with minor suggestions

This is a high-quality implementation of a modern IPv6-first router configuration. The architecture is sound, demonstrating deep understanding of IPv6, DNS64, and NAT64 technologies. The use of network namespace isolation is particularly clever, providing both security and functionality benefits.

Key Highlights:

• Excellent architectural design with proper isolation boundaries
• Comprehensive documentation explaining design decisions
• Production-ready with monitoring and error handling
• Forward-looking IPv6-first approach aligning with industry direction

Suggested Next Steps:

1. Consider implementing the security hardening recommendations (rate limiting, connection limits)
2. Add the suggested configurability for port ranges and resource limits
3. Document the DNS resolution flow and troubleshooting steps
4. Consider adding integration tests for the NAT64 translation path

The code is well-written, properly documented, and ready for production deployment. The minor suggestions above would enhance robustness but are not blockers.