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Revert to VPN original MTU (set by WIREGUARD_MTU for example) if ICMP fails

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This commit is contained in:
Quentin McGaw
2025-10-03 14:16:47 +00:00
parent b6e873cf25
commit c0ebd180cb
2 changed files with 6 additions and 4 deletions
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1
internal/configuration/settings/wireguard.go
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@@ -45,6 +45,7 @@ type Wireguard struct {
// It has been lowered to 1320 following quite a bit of // It has been lowered to 1320 following quite a bit of
// investigation in the issue: // investigation in the issue:
// https://github.com/qdm12/gluetun/issues/2533. // https://github.com/qdm12/gluetun/issues/2533.
// Note this should now be replaced with the PMTUD feature.
MTU uint16 `json:"mtu"` MTU uint16 `json:"mtu"`
// Implementation is the Wireguard implementation to use. // Implementation is the Wireguard implementation to use.
// It can be "auto", "userspace" or "kernelspace". // It can be "auto", "userspace" or "kernelspace".

9
internal/vpn/tunnelup.go
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@@ -95,6 +95,8 @@ func updateToMaxMTU(ctx context.Context, vpnInterface string,
return fmt.Errorf("getting VPN interface by name: %w", err) return fmt.Errorf("getting VPN interface by name: %w", err)
} }
originalMTU := link.MTU
// Note: no point testing for an MTU of 1500, it will never work due to the VPN // Note: no point testing for an MTU of 1500, it will never work due to the VPN
// protocol overhead, so start lower than 1500 according to the protocol used. // protocol overhead, so start lower than 1500 according to the protocol used.
const physicalLinkMTU = 1500 const physicalLinkMTU = 1500
@@ -123,10 +125,9 @@ func updateToMaxMTU(ctx context.Context, vpnInterface string,
case err == nil: case err == nil:
logger.Infof("Setting VPN interface %s MTU to maximum valid MTU %d", vpnInterface, vpnLinkMTU) logger.Infof("Setting VPN interface %s MTU to maximum valid MTU %d", vpnInterface, vpnLinkMTU)
case errors.Is(err, pmtud.ErrMTUNotFound): case errors.Is(err, pmtud.ErrMTUNotFound):
const conservativeMTU = 1300 vpnLinkMTU = int(originalMTU)
vpnLinkMTU = conservativeMTU logger.Infof("Reverting VPN interface %s MTU to %d (due to: %s)",
logger.Infof("Setting VPN interface %s MTU to a conservative MTU of %d (due to: %s)", vpnInterface, originalMTU, err)
vpnInterface, conservativeMTU, err)
default: default:
return fmt.Errorf("path MTU discovering: %w", err) return fmt.Errorf("path MTU discovering: %w", err)
} }