Merge pull request microsoft#117 from Microsoft/mtu

Sets the MTU when a non-default value is specified

Author: soccerGB

service/gcs/prot/protocol.go

@@ -438,6 +438,7 @@ type NetworkAdapter struct {
 	HostDNSServerList  string `json:"HostDnsServerList,omitempty"`
 	HostDNSSuffix      string `json:"HostDnsSuffix,omitempty"`
 	EnableLowMetric    bool   `json:",omitempty"`
+	EncapOverhead      uint16 `json:",omitempty"`
 }
 
 // MappedVirtualDisk represents a disk on the host which is mapped into a

service/gcsutils/gcstools/netnsConfig.go

@@ -98,6 +98,14 @@ func netnsConfig() error {
 		return fmt.Errorf("netlink.LinkByName(%s) failed: %v", *ifStr, err)
 	}
 
+	// User requested non-default MTU size
+	if a.EncapOverhead != 0 {
+		mtu := link.Attrs().MTU - int(a.EncapOverhead)
+		if err = netlink.LinkSetMTU(link, mtu); err != nil {
+			return fmt.Errorf("netlink.LinkSetMTU(%#v, %d) failed: %v", link, mtu, err)
+		}
+	}
+
 	// Configure the interface
 	if a.NatEnabled {
 		metric := 1