Add IPv6 support for LinuxContainer

LinuxContainer was missing IPv6 configuration that LinuxPod already had.
This adds the missing calls to configure IPv6 addresses and routes on
container network interfaces.

Changes:
- LinuxContainer.swift: Add IPv6 address and route configuration
- Interface/NATInterface/NATNetworkInterface: IPv6 fields
- SandboxContext proto/grpc: IPv6 methods for guest agent
- VirtualMachineAgent/Vminitd: IPv6 implementation
- NetlinkSession: IPv6 netlink support

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

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

Author: yordsel

Sources/Containerization/Interface.swift

@@ -25,6 +25,13 @@ public protocol Interface: Sendable {
     /// The IP address for the default route, or nil for no default route.
     var ipv4Gateway: IPv4Address? { get }
 
+    /// The interface IPv6 address and subnet prefix length, as a CIDR address.
+    /// Example: `fdef:4eb5:9ccb:341e:fc98:82ff:fe82:4f28/64`
+    var ipv6Address: CIDRv6? { get }
+
+    /// The IPv6 address for the default route, or nil for no default route.
+    var ipv6Gateway: IPv6Address? { get }
+
     /// The interface MAC address, or nil to auto-configure the address.
     var macAddress: MACAddress? { get }
 
@@ -34,4 +41,6 @@ public protocol Interface: Sendable {
 
 extension Interface {
     public var mtu: UInt32 { 1500 }
+    public var ipv6Address: CIDRv6? { nil }
+    public var ipv6Gateway: IPv6Address? { nil }
 }

Sources/Containerization/LinuxContainer.swift

@@ -474,9 +474,11 @@ extension LinuxContainer {
                     }
 
                     // For every interface asked for:
-                    // 1. Add the address requested
+                    // 1. Add the IPv4 address requested
                     // 2. Online the adapter
-                    // 3. If a gateway IP address is present, add the default route.
+                    // 3. If an IPv4 gateway IP address is present, add the default route.
+                    // 4. Add the IPv6 address if present
+                    // 5. If an IPv6 gateway IP address is present, add the IPv6 default route.
                     for (index, i) in self.interfaces.enumerated() {
                         let name = "eth\(index)"
                         self.logger?.debug("setting up interface \(name) with address \(i.ipv4Address)")
@@ -489,6 +491,15 @@ extension LinuxContainer {
                             }
                             try await agent.routeAddDefault(name: name, ipv4Gateway: ipv4Gateway)
                         }
+
+                        // Configure IPv6 if address is present
+                        if let ipv6Address = i.ipv6Address {
+                            self.logger?.debug("setting up interface \(name) with IPv6 address \(ipv6Address)")
+                            try await agent.addressAdd(name: name, ipv6Address: ipv6Address)
+                            if let ipv6Gateway = i.ipv6Gateway {
+                                try await agent.routeAddDefault(name: name, ipv6Gateway: ipv6Gateway)
+                            }
+                        }
                     }
 
                     // Setup /etc/resolv.conf and /etc/hosts if asked for.

Sources/Containerization/LinuxPod.swift

@@ -424,9 +424,11 @@ extension LinuxPod {
                     }
 
                     // For every interface asked for:
-                    // 1. Add the address requested
+                    // 1. Add the IPv4 address requested
                     // 2. Online the adapter
-                    // 3. If a gateway IP address is present, add the default route.
+                    // 3. If an IPv4 gateway IP address is present, add the default route.
+                    // 4. Add the IPv6 address if present
+                    // 5. If an IPv6 gateway IP address is present, add the IPv6 default route.
                     for (index, i) in self.interfaces.enumerated() {
                         let name = "eth\(index)"
                         self.logger?.debug("setting up interface \(name) with address \(i.ipv4Address)")
@@ -439,6 +441,15 @@ extension LinuxPod {
                             }
                             try await agent.routeAddDefault(name: name, ipv4Gateway: ipv4Gateway)
                         }
+
+                        // Configure IPv6 if address is present
+                        if let ipv6Address = i.ipv6Address {
+                            self.logger?.debug("setting up interface \(name) with IPv6 address \(ipv6Address)")
+                            try await agent.addressAdd(name: name, ipv6Address: ipv6Address)
+                            if let ipv6Gateway = i.ipv6Gateway {
+                                try await agent.routeAddDefault(name: name, ipv6Gateway: ipv6Gateway)
+                            }
+                        }
                     }
 
                     // Setup /etc/resolv.conf and /etc/hosts for each container.

Sources/Containerization/NATInterface.swift

@@ -19,12 +19,23 @@ import ContainerizationExtras
 public struct NATInterface: Interface {
     public var ipv4Address: CIDRv4
     public var ipv4Gateway: IPv4Address?
+    public var ipv6Address: CIDRv6?
+    public var ipv6Gateway: IPv6Address?
     public var macAddress: MACAddress?
     public var mtu: UInt32
 
-    public init(ipv4Address: CIDRv4, ipv4Gateway: IPv4Address?, macAddress: MACAddress? = nil, mtu: UInt32 = 1500) {
+    public init(
+        ipv4Address: CIDRv4,
+        ipv4Gateway: IPv4Address?,
+        ipv6Address: CIDRv6? = nil,
+        ipv6Gateway: IPv6Address? = nil,
+        macAddress: MACAddress? = nil,
+        mtu: UInt32 = 1500
+    ) {
         self.ipv4Address = ipv4Address
         self.ipv4Gateway = ipv4Gateway
+        self.ipv6Address = ipv6Address
+        self.ipv6Gateway = ipv6Gateway
         self.macAddress = macAddress
         self.mtu = mtu
     }

Sources/Containerization/NATNetworkInterface.swift

@@ -29,6 +29,8 @@ import Synchronization
 public final class NATNetworkInterface: Interface, Sendable {
     public let ipv4Address: CIDRv4
     public let ipv4Gateway: IPv4Address?
+    public let ipv6Address: CIDRv6?
+    public let ipv6Gateway: IPv6Address?
     public let macAddress: MACAddress?
     public let mtu: UInt32
 
@@ -40,12 +42,16 @@ public final class NATNetworkInterface: Interface, Sendable {
     public init(
         ipv4Address: CIDRv4,
         ipv4Gateway: IPv4Address?,
+        ipv6Address: CIDRv6? = nil,
+        ipv6Gateway: IPv6Address? = nil,
         reference: sending vmnet_network_ref,
         macAddress: MACAddress? = nil,
         mtu: UInt32 = 1500
     ) {
         self.ipv4Address = ipv4Address
         self.ipv4Gateway = ipv4Gateway
+        self.ipv6Address = ipv6Address
+        self.ipv6Gateway = ipv6Gateway
         self.macAddress = macAddress
         self.mtu = mtu
         self.reference = reference
@@ -55,11 +61,15 @@ public final class NATNetworkInterface: Interface, Sendable {
     public init(
         ipv4Address: CIDRv4,
         ipv4Gateway: IPv4Address?,
+        ipv6Address: CIDRv6? = nil,
+        ipv6Gateway: IPv6Address? = nil,
         macAddress: MACAddress? = nil,
         mtu: UInt32 = 1500
     ) {
         self.ipv4Address = ipv4Address
         self.ipv4Gateway = ipv4Gateway
+        self.ipv6Address = ipv6Address
+        self.ipv6Gateway = ipv6Gateway
         self.macAddress = macAddress
         self.mtu = mtu
         self.reference = nil