Add IPv6 gateway support for container networking

Add ipv6Gateway field to network attachments and status to enable
proper IPv6 routing in containers. This complements the existing
ipv6Address/ipv6Subnet fields.

Changes:
- Attachment: Add ipv6Gateway field
- NetworkState: Add ipv6Gateway to NetworkStatus
- IsolatedInterfaceStrategy: Pass IPv6 gateway to NATInterface
- NonisolatedInterfaceStrategy: Pass IPv6 gateway to NATNetworkInterface
- NetworkService: Include ipv6Gateway in attachment creation
- ReservedVmnetNetwork: Calculate and store ipv6Gateway

Depends on: apple/containerization IPv6 support

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Sources/ContainerResource/Network/Attachment.swift

@@ -29,6 +29,9 @@ public struct Attachment: Codable, Sendable {
     /// The CIDR address describing the interface IPv6 address, with the prefix length of the subnet.
     /// The address is nil if the IPv6 subnet could not be determined at network creation time.
     public let ipv6Address: CIDRv6?
+    /// The IPv6 gateway address.
+    /// The value is nil if the IPv6 subnet could not be determined at network creation time.
+    public let ipv6Gateway: IPv6Address?
     /// The MAC address associated with the attachment (optional).
     public let macAddress: MACAddress?
 
@@ -38,13 +41,15 @@ public struct Attachment: Codable, Sendable {
         ipv4Address: CIDRv4,
         ipv4Gateway: IPv4Address,
         ipv6Address: CIDRv6?,
+        ipv6Gateway: IPv6Address? = nil,
         macAddress: MACAddress?
     ) {
         self.network = network
         self.hostname = hostname
         self.ipv4Address = ipv4Address
         self.ipv4Gateway = ipv4Gateway
         self.ipv6Address = ipv6Address
+        self.ipv6Gateway = ipv6Gateway
         self.macAddress = macAddress
     }
 }

Sources/ContainerResource/Network/NetworkState.swift

@@ -30,14 +30,20 @@ public struct NetworkStatus: Codable, Sendable {
     /// The value is nil if the IPv6 subnet cannot be determined at creation time.
     public let ipv6Subnet: CIDRv6?
 
+    /// The gateway IPv6 address.
+    /// The value is nil if the IPv6 subnet cannot be determined at creation time.
+    public let ipv6Gateway: IPv6Address?
+
     public init(
         ipv4Subnet: CIDRv4,
         ipv4Gateway: IPv4Address,
         ipv6Subnet: CIDRv6?,
+        ipv6Gateway: IPv6Address? = nil
     ) {
         self.ipv4Subnet = ipv4Subnet
         self.ipv4Gateway = ipv4Gateway
         self.ipv6Subnet = ipv6Subnet
+        self.ipv6Gateway = ipv6Gateway
     }
 }
 

Sources/Helpers/RuntimeLinux/IsolatedInterfaceStrategy.swift

@@ -25,9 +25,12 @@ import Containerization
 struct IsolatedInterfaceStrategy: InterfaceStrategy {
     public func toInterface(attachment: Attachment, interfaceIndex: Int, additionalData: XPCMessage?) -> Interface {
         let ipv4Gateway = interfaceIndex == 0 ? attachment.ipv4Gateway : nil
+        let ipv6Gateway = interfaceIndex == 0 ? attachment.ipv6Gateway : nil
         return NATInterface(
             ipv4Address: attachment.ipv4Address,
             ipv4Gateway: ipv4Gateway,
+            ipv6Address: attachment.ipv6Address,
+            ipv6Gateway: ipv6Gateway,
             macAddress: attachment.macAddress,
             // https://github.com/apple/containerization/pull/38
             mtu: 1280

Sources/Helpers/RuntimeLinux/NonisolatedInterfaceStrategy.swift

@@ -44,9 +44,12 @@ struct NonisolatedInterfaceStrategy: InterfaceStrategy {
 
         log.info("creating NATNetworkInterface with network reference")
         let ipv4Gateway = interfaceIndex == 0 ? attachment.ipv4Gateway : nil
+        let ipv6Gateway = interfaceIndex == 0 ? attachment.ipv6Gateway : nil
         return NATNetworkInterface(
             ipv4Address: attachment.ipv4Address,
             ipv4Gateway: ipv4Gateway,
+            ipv6Address: attachment.ipv6Address,
+            ipv6Gateway: ipv6Gateway,
             reference: networkRef,
             macAddress: attachment.macAddress,
             // https://github.com/apple/containerization/pull/38

Sources/Services/ContainerNetworkService/Server/NetworkService.swift

@@ -77,6 +77,7 @@ public actor NetworkService: Sendable {
             ipv4Address: try CIDRv4(ip, prefix: status.ipv4Subnet.prefix),
             ipv4Gateway: status.ipv4Gateway,
             ipv6Address: ipv6Address,
+            ipv6Gateway: status.ipv6Gateway,
             macAddress: macAddress
         )
         log?.info(
@@ -86,6 +87,7 @@ public actor NetworkService: Sendable {
                 "ipv4Address": "\(attachment.ipv4Address)",
                 "ipv4Gateway": "\(attachment.ipv4Gateway)",
                 "ipv6Address": "\(attachment.ipv6Address?.description ?? "unavailable")",
+                "ipv6Gateway": "\(attachment.ipv6Gateway?.description ?? "unavailable")",
                 "macAddress": "\(attachment.macAddress?.description ?? "unspecified")",
             ])
         let reply = message.reply()
@@ -136,6 +138,7 @@ public actor NetworkService: Sendable {
             ipv4Address: ipv4Address,
             ipv4Gateway: status.ipv4Gateway,
             ipv6Address: ipv6Address,
+            ipv6Gateway: status.ipv6Gateway,
             macAddress: macAddress
         )
         log?.debug(

Sources/Services/ContainerNetworkService/Server/ReservedVmnetNetwork.swift

@@ -41,6 +41,7 @@ public final class ReservedVmnetNetwork: Network {
         let ipv4Subnet: CIDRv4
         let ipv4Gateway: IPv4Address
         let ipv6Subnet: CIDRv6
+        let ipv6Gateway: IPv6Address
     }
 
     private let stateMutex: Mutex<State>
@@ -85,6 +86,7 @@ public final class ReservedVmnetNetwork: Network {
                 ipv4Subnet: networkInfo.ipv4Subnet,
                 ipv4Gateway: networkInfo.ipv4Gateway,
                 ipv6Subnet: networkInfo.ipv6Subnet,
+                ipv6Gateway: networkInfo.ipv6Gateway
             )
             state.networkState = NetworkState.running(configuration, networkStatus)
             state.network = networkInfo.network
@@ -183,6 +185,7 @@ public final class ReservedVmnetNetwork: Network {
         }
         let prefixIpv6Addr = try IPv6Address(prefixIpv6Bytes)
         let runningV6Subnet = try CIDRv6(prefixIpv6Addr, prefix: prefix)
+        let runningV6Gateway = IPv6Address(runningV6Subnet.lower.value + 1)
 
         log.info(
             "started vmnet network",
@@ -199,6 +202,7 @@ public final class ReservedVmnetNetwork: Network {
             ipv4Subnet: runningSubnet,
             ipv4Gateway: runningGateway,
             ipv6Subnet: runningV6Subnet,
+            ipv6Gateway: runningV6Gateway
         )
     }
 }