diff --git a/machines/back.nix b/machines/back.nix
index 9618f90..56f4c4a 100644
--- a/machines/back.nix
+++ b/machines/back.nix
@@ -69,4 +69,14 @@
   };
 
   services.openssh.settings.AllowUsers = [ "backup" ];
+
+  systemd.services.switch-mlx4-ports-to-eth = {
+    serviceConfig.Type = "oneshot";
+    description = "switch Mellanox ConnectX-3 Pro ports to ethernet mode";
+    script = ''
+      echo eth >/sys/bus/pci/devices/0000\:04\:00.0/mlx4_port1
+      echo eth >/sys/bus/pci/devices/0000\:04\:00.0/mlx4_port2
+    '';
+    wantedBy = [ "multi-user.target" ];
+  };
 }