diff --git a/core/execution.go b/core/execution.go
index cad4e84aa2..5e0cbd37ed 100644
--- a/core/execution.go
+++ b/core/execution.go
@@ -33,8 +33,7 @@ func (self *Execution) Call(codeAddr []byte, caller vm.ContextRef) ([]byte, erro
 
 func (self *Execution) exec(code, contextAddr []byte, caller vm.ContextRef) (ret []byte, err error) {
 	env := self.env
-	evm := vm.New(env)
-
+	evm := vm.NewVm(env)
 	if env.Depth() == vm.MaxCallDepth {
 		caller.ReturnGas(self.Gas, self.price)
 
diff --git a/core/state_transition.go b/core/state_transition.go
index 8b0ca2ac4b..00d9d486af 100644
--- a/core/state_transition.go
+++ b/core/state_transition.go
@@ -10,6 +10,8 @@ import (
 	"github.com/ethereum/go-ethereum/vm"
 )
 
+const tryJit = false
+
 /*
  * The State transitioning model
  *
@@ -184,6 +186,7 @@ func (self *StateTransition) TransitionState() (ret []byte, err error) {
 		return
 	}
 
+	stateCopy := self.env.State().Copy()
 	vmenv := self.env
 	var ref vm.ContextRef
 	if MessageCreatesContract(msg) {
@@ -196,8 +199,30 @@ func (self *StateTransition) TransitionState() (ret []byte, err error) {
 				ref.SetCode(ret)
 			}
 		}
+
+		if vmenv, ok := vmenv.(*VMEnv); ok && tryJit {
+			statelogger.Infof("CREATE: re-running using JIT (PH=%x)\n", stateCopy.Root()[:4])
+			// re-run using the JIT (validation for the JIT)
+			goodState := vmenv.State().Copy()
+			vmenv.state = stateCopy
+			vmenv.SetVmType(vm.JitVmTy)
+			vmenv.Create(sender, contract.Address(), self.msg.Data(), self.gas, self.gasPrice, self.value)
+			statelogger.Infof("DONE PH=%x STD_H=%x JIT_H=%x\n", stateCopy.Root()[:4], goodState.Root()[:4], vmenv.State().Root()[:4])
+			self.state.Set(goodState)
+		}
 	} else {
 		ret, err = vmenv.Call(self.From(), self.To().Address(), self.msg.Data(), self.gas, self.gasPrice, self.value)
+
+		if vmenv, ok := vmenv.(*VMEnv); ok && tryJit {
+			statelogger.Infof("CALL: re-running using JIT (PH=%x)\n", stateCopy.Root()[:4])
+			// re-run using the JIT (validation for the JIT)
+			goodState := vmenv.State().Copy()
+			vmenv.state = stateCopy
+			vmenv.SetVmType(vm.JitVmTy)
+			vmenv.Call(self.From(), self.To().Address(), self.msg.Data(), self.gas, self.gasPrice, self.value)
+			statelogger.Infof("DONE PH=%x STD_H=%x JIT_H=%x\n", stateCopy.Root()[:4], goodState.Root()[:4], vmenv.State().Root()[:4])
+			self.state.Set(goodState)
+		}
 	}
 
 	if err != nil {
diff --git a/core/vm_env.go b/core/vm_env.go
index 624a633334..c7491bcdc7 100644
--- a/core/vm_env.go
+++ b/core/vm_env.go
@@ -14,6 +14,7 @@ type VMEnv struct {
 	msg   Message
 	depth int
 	chain *ChainManager
+	typ   vm.Type
 }
 
 func NewEnv(state *state.StateDB, chain *ChainManager, msg Message, block *types.Block) *VMEnv {
@@ -22,6 +23,7 @@ func NewEnv(state *state.StateDB, chain *ChainManager, msg Message, block *types
 		state: state,
 		block: block,
 		msg:   msg,
+		typ:   vm.StdVmTy,
 	}
 }
 
@@ -35,6 +37,8 @@ func (self *VMEnv) Value() *big.Int       { return self.msg.Value() }
 func (self *VMEnv) State() *state.StateDB { return self.state }
 func (self *VMEnv) Depth() int            { return self.depth }
 func (self *VMEnv) SetDepth(i int)        { self.depth = i }
+func (self *VMEnv) VmType() vm.Type       { return self.typ }
+func (self *VMEnv) SetVmType(t vm.Type)   { self.typ = t }
 func (self *VMEnv) GetHash(n uint64) []byte {
 	if block := self.chain.GetBlockByNumber(n); block != nil {
 		return block.Hash()
diff --git a/eth/backend.go b/eth/backend.go
index b7b5c5f855..a8db3ab201 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -141,14 +141,13 @@ func New(config *Config) (*Ethereum, error) {
 	if err != nil {
 		return nil, err
 	}
-	fmt.Println(nat)
 
 	eth.net = &p2p.Server{
 		Identity:  clientId,
 		MaxPeers:  config.MaxPeers,
 		Protocols: protocols,
 		Blacklist: eth.blacklist,
-		NAT:       p2p.UPNP(),
+		NAT:       nat,
 		NoDial:    !config.Dial,
 	}
 
diff --git a/vm/common.go b/vm/common.go
index ff187001f8..45a7187a99 100644
--- a/vm/common.go
+++ b/vm/common.go
@@ -18,6 +18,18 @@ const (
 	MaxVmTy
 )
 
+func NewVm(env Environment) VirtualMachine {
+	switch env.VmType() {
+	case JitVmTy:
+		return NewJitVm(env)
+	default:
+		vmlogger.Infoln("unsupported vm type %d", env.VmType())
+		fallthrough
+	case StdVmTy:
+		return New(env)
+	}
+}
+
 var (
 	GasStep         = big.NewInt(1)
 	GasSha          = big.NewInt(10)