Merge branch 'wg-fix-ipv6-mtu'

5 files changed, 22 insertions, 7 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44402cdbad..72e2327d50 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,6 +28,9 @@ Line wrap the file at 100 chars.                                              Th
 ### Fixed
 - Fix `mullvad-cli` panicking if it tried to write to a closed pipe on Linux and macOS.
 
+#### Windows
+- Fix error setting up tunnel when MTU was incorrectly set to a value below 1280 for IPv6.
+
 
 ## [2025.5-beta1] - 2025-03-11
 ### Added
diff --git a/talpid-openvpn/src/wintun.rs b/talpid-openvpn/src/wintun.rs
index f8592ef94c..a77ce81e02 100644
--- a/talpid-openvpn/src/wintun.rs
+++ b/talpid-openvpn/src/wintun.rs
@@ -98,7 +98,7 @@ impl WintunAdapter {
 
     pub fn prepare_interface(&self) {
         if let Err(error) =
-            talpid_tunnel::network_interface::initialize_interfaces(self.luid(), None)
+            talpid_tunnel::network_interface::initialize_interfaces(self.luid(), None, None)
         {
             log::error!(
                 "{}",
diff --git a/talpid-tunnel/src/windows.rs b/talpid-tunnel/src/windows.rs
index bc5fffb3f0..109e6a9ae1 100644
--- a/talpid-tunnel/src/windows.rs
+++ b/talpid-tunnel/src/windows.rs
@@ -7,8 +7,15 @@ use windows_sys::Win32::{
 
 /// Sets MTU, metric, and disables unnecessary features for the IP interfaces
 /// on the specified network interface (identified by `luid`).
-pub fn initialize_interfaces(luid: NET_LUID_LH, mtu: Option<u32>) -> io::Result<()> {
-    for family in &[AddressFamily::Ipv4, AddressFamily::Ipv6] {
+pub fn initialize_interfaces(
+    luid: NET_LUID_LH,
+    ipv4_mtu: Option<u32>,
+    ipv6_mtu: Option<u32>,
+) -> io::Result<()> {
+    for (family, mtu) in &[
+        (AddressFamily::Ipv4, ipv4_mtu),
+        (AddressFamily::Ipv6, ipv6_mtu),
+    ] {
         let mut row = match get_ip_interface_entry(*family, &luid) {
             Ok(row) => row,
             Err(error) if error.raw_os_error() == Some(ERROR_NOT_FOUND as i32) => continue,
@@ -16,7 +23,7 @@ pub fn initialize_interfaces(luid: NET_LUID_LH, mtu: Option<u32>) -> io::Result<
         };
 
         if let Some(mtu) = mtu {
-            row.NlMtu = mtu;
+            row.NlMtu = *mtu;
         }
 
         // Disable DAD, DHCP, and router discovery
diff --git a/talpid-wireguard/src/wireguard_go/mod.rs b/talpid-wireguard/src/wireguard_go/mod.rs
index 0289831172..2f315c82cb 100644
--- a/talpid-wireguard/src/wireguard_go/mod.rs
+++ b/talpid-wireguard/src/wireguard_go/mod.rs
@@ -311,7 +311,8 @@ impl WgGoTunnel {
                 .map_err(|e| BoxedError::new(TunnelError::SetupIpInterfaces(e)))?;
             log::debug!("Waiting for tunnel IP interfaces: Done");
 
-            if let Err(error) = talpid_tunnel::network_interface::initialize_interfaces(luid, None)
+            if let Err(error) =
+                talpid_tunnel::network_interface::initialize_interfaces(luid, None, None)
             {
                 log::error!(
                     "{}",
diff --git a/talpid-wireguard/src/wireguard_nt/mod.rs b/talpid-wireguard/src/wireguard_nt/mod.rs
index ff5b082490..baac2ddd69 100644
--- a/talpid-wireguard/src/wireguard_nt/mod.rs
+++ b/talpid-wireguard/src/wireguard_nt/mod.rs
@@ -543,8 +543,12 @@ async fn setup_ip_listener(device: Arc<WgNtAdapter>, mtu: u32, has_ipv6: bool) -
         .map_err(Error::IpInterfaces)?;
     log::debug!("Waiting for tunnel IP interfaces: Done");
 
-    talpid_tunnel::network_interface::initialize_interfaces(luid, Some(mtu))
-        .map_err(Error::SetTunnelMtu)?;
+    talpid_tunnel::network_interface::initialize_interfaces(
+        luid,
+        Some(mtu),
+        has_ipv6.then_some(mtu),
+    )
+    .map_err(Error::SetTunnelMtu)?;
 
     device
         .set_state(WgAdapterState::Up)