Allow proxy to run on systems with iptables <1.4.11

pkg/util/iptables/iptables.go

@@ -18,8 +18,12 @@ package iptables
 
 import (
 	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
 	"sync"
 
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
 	utilexec "github.com/GoogleCloudPlatform/kubernetes/pkg/util/exec"
 	"github.com/golang/glog"
 )
@@ -100,7 +104,7 @@ func (runner *runner) EnsureRule(table Table, chain Chain, args ...string) (bool
 	runner.mu.Lock()
 	defer runner.mu.Unlock()
 
-	exists, err := runner.checkRule(fullArgs)
+	exists, err := runner.checkRule(table, chain, args...)
 	if err != nil {
 		return false, err
 	}
@@ -121,7 +125,7 @@ func (runner *runner) DeleteRule(table Table, chain Chain, args ...string) error
 	runner.mu.Lock()
 	defer runner.mu.Unlock()
 
-	exists, err := runner.checkRule(fullArgs)
+	exists, err := runner.checkRule(table, chain, args...)
 	if err != nil {
 		return err
 	}
@@ -146,7 +150,47 @@ func (runner *runner) run(op operation, args []string) ([]byte, error) {
 
 // Returns (bool, nil) if it was able to check the existence of the rule, or
 // (<undefined>, error) if the process of checking failed.
-func (runner *runner) checkRule(args []string) (bool, error) {
+func (runner *runner) checkRule(table Table, chain Chain, args ...string) (bool, error) {
+	checkPresent, err := getIptablesHasCheckCommand(runner.exec)
+	if err != nil {
+		glog.Warning("Error checking iptables version, assuming version at least 1.4.11: %v", err)
+		checkPresent = true
+	}
+	if checkPresent {
+		return runner.checkRuleUsingCheck(makeFullArgs(table, chain, args...))
+	} else {
+		return runner.checkRuleWithoutCheck(table, chain, args...)
+	}
+}
+
+// Executes the rule check without using the "-C" flag, instead parsing iptables-save.
+// Present for compatibility with <1.4.11 versions of iptables.
+func (runner *runner) checkRuleWithoutCheck(table Table, chain Chain, args ...string) (bool, error) {
+	out, err := runner.exec.Command("iptables-save", "-t", string(table)).CombinedOutput()
+	if err != nil {
+		return false, fmt.Errorf("error checking rule: %s", err)
+	}
+
+	argset := util.NewStringSet(args...)
+
+	for _, line := range strings.Split(string(out), "\n") {
+		var fields = strings.Fields(line)
+
+		// Check that this is a rule for the correct chain, and that it has
+		// the correct number of argument (+2 for "-A <chain name>")
+		if strings.HasPrefix(line, fmt.Sprintf("-A %s", string(chain))) && len(fields) == len(args)+2 {
+			// TODO: This misses reorderings e.g. "-x foo ! -y bar" will match "! -x foo -y bar"
+			if util.NewStringSet(fields...).IsSuperset(argset) {
+				return true, nil
+			}
+		}
+	}
+
+	return false, nil
+}
+
+// Executes the rule check using the "-C" flag
+func (runner *runner) checkRuleUsingCheck(args []string) (bool, error) {
 	out, err := runner.run(opCheckRule, args)
 	if err == nil {
 		return true, nil
@@ -174,3 +218,69 @@ const (
 func makeFullArgs(table Table, chain Chain, args ...string) []string {
 	return append([]string{string(chain), "-t", string(table)}, args...)
 }
+
+// Checks if iptables has the "-C" flag
+func getIptablesHasCheckCommand(exec utilexec.Interface) (bool, error) {
+	vstring, err := getIptablesVersionString(exec)
+	if err != nil {
+		return false, err
+	}
+
+	v1, v2, v3, err := extractIptablesVersion(vstring)
+	if err != nil {
+		return false, err
+	}
+
+	return iptablesHasCheckCommand(v1, v2, v3), nil
+}
+
+// getIptablesVersion returns the first three components of the iptables version.
+// e.g. "iptables v1.3.66" would return (1, 3, 66, nil)
+func extractIptablesVersion(str string) (int, int, int, error) {
+	versionMatcher := regexp.MustCompile("v([0-9]+)\\.([0-9]+)\\.([0-9]+)")
+	result := versionMatcher.FindStringSubmatch(str)
+	if result == nil {
+		return 0, 0, 0, fmt.Errorf("No iptables version found in string: %s", str)
+	}
+
+	v1, err := strconv.Atoi(result[1])
+	if err != nil {
+		return 0, 0, 0, err
+	}
+
+	v2, err := strconv.Atoi(result[2])
+	if err != nil {
+		return 0, 0, 0, err
+	}
+
+	v3, err := strconv.Atoi(result[3])
+	if err != nil {
+		return 0, 0, 0, err
+	}
+
+	return v1, v2, v3, nil
+}
+
+// Runs "iptables --version" to get the version string
+func getIptablesVersionString(exec utilexec.Interface) (string, error) {
+	bytes, err := exec.Command("iptables", "--version").CombinedOutput()
+	if err != nil {
+		return "", err
+	}
+
+	return string(bytes), nil
+}
+
+// Checks if an iptables version is after 1.4.11, when --check was added
+func iptablesHasCheckCommand(v1 int, v2 int, v3 int) bool {
+	if v1 > 1 {
+		return true
+	}
+	if v1 == 1 && v2 > 4 {
+		return true
+	}
+	if v1 == 1 && v2 == 4 && v3 >= 11 {
+		return true
+	}
+	return false
+}

pkg/util/iptables/iptables_test.go

@@ -108,13 +108,17 @@ func TestFlushChain(t *testing.T) {
 func TestEnsureRuleAlreadyExists(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Success.
 			func() ([]byte, error) { return []byte{}, nil },
 		},
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Success of that exec means "done".
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Success of that exec means "done".
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
 	}
@@ -126,10 +130,10 @@ func TestEnsureRuleAlreadyExists(t *testing.T) {
 	if !exists {
 		t.Errorf("expected exists = true")
 	}
-	if fcmd.CombinedOutputCalls != 1 {
-		t.Errorf("expected 1 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 2 {
+		t.Errorf("expected 2 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
 	}
-	if !util.NewStringSet(fcmd.CombinedOutputLog[0]...).HasAll("iptables", "-t", "nat", "-C", "OUTPUT", "abc", "123") {
+	if !util.NewStringSet(fcmd.CombinedOutputLog[1]...).HasAll("iptables", "-t", "nat", "-C", "OUTPUT", "abc", "123") {
 		t.Errorf("wrong CombinedOutput() log, got %s", fcmd.CombinedOutputLog[0])
 	}
 }
@@ -137,6 +141,8 @@ func TestEnsureRuleAlreadyExists(t *testing.T) {
 func TestEnsureRuleNew(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Status 1 on the first call.
 			func() ([]byte, error) { return nil, &exec.FakeExitError{1} },
 			// Success on the second call.
@@ -145,7 +151,9 @@ func TestEnsureRuleNew(t *testing.T) {
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Failure of that means create it.
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Failure of that means create it.
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
@@ -158,10 +166,10 @@ func TestEnsureRuleNew(t *testing.T) {
 	if exists {
 		t.Errorf("expected exists = false")
 	}
-	if fcmd.CombinedOutputCalls != 2 {
-		t.Errorf("expected 2 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 3 {
+		t.Errorf("expected 3 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
 	}
-	if !util.NewStringSet(fcmd.CombinedOutputLog[1]...).HasAll("iptables", "-t", "nat", "-A", "OUTPUT", "abc", "123") {
+	if !util.NewStringSet(fcmd.CombinedOutputLog[2]...).HasAll("iptables", "-t", "nat", "-A", "OUTPUT", "abc", "123") {
 		t.Errorf("wrong CombinedOutput() log, got %s", fcmd.CombinedOutputLog[1])
 	}
 }
@@ -169,13 +177,17 @@ func TestEnsureRuleNew(t *testing.T) {
 func TestEnsureRuleErrorChecking(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Status 2 on the first call.
 			func() ([]byte, error) { return nil, &exec.FakeExitError{2} },
 		},
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Failure of that means create it.
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Failure of that means create it.
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
 	}
@@ -184,14 +196,16 @@ func TestEnsureRuleErrorChecking(t *testing.T) {
 	if err == nil {
 		t.Errorf("expected failure")
 	}
-	if fcmd.CombinedOutputCalls != 1 {
-		t.Errorf("expected 1 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 2 {
+		t.Errorf("expected 2 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
 	}
 }
 
 func TestEnsureRuleErrorCreating(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Status 1 on the first call.
 			func() ([]byte, error) { return nil, &exec.FakeExitError{1} },
 			// Status 1 on the second call.
@@ -200,7 +214,9 @@ func TestEnsureRuleErrorCreating(t *testing.T) {
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Failure of that means create it.
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Failure of that means create it.
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
@@ -210,21 +226,25 @@ func TestEnsureRuleErrorCreating(t *testing.T) {
 	if err == nil {
 		t.Errorf("expected failure")
 	}
-	if fcmd.CombinedOutputCalls != 2 {
-		t.Errorf("expected 2 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 3 {
+		t.Errorf("expected 3 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
 	}
 }
 
 func TestDeleteRuleAlreadyExists(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Status 1 on the first call.
 			func() ([]byte, error) { return nil, &exec.FakeExitError{1} },
 		},
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Failure of that exec means "does not exist".
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Failure of that exec means "does not exist".
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
 	}
@@ -233,10 +253,10 @@ func TestDeleteRuleAlreadyExists(t *testing.T) {
 	if err != nil {
 		t.Errorf("expected success, got %+v", err)
 	}
-	if fcmd.CombinedOutputCalls != 1 {
-		t.Errorf("expected 1 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 2 {
+		t.Errorf("expected 2 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
 	}
-	if !util.NewStringSet(fcmd.CombinedOutputLog[0]...).HasAll("iptables", "-t", "nat", "-C", "OUTPUT", "abc", "123") {
+	if !util.NewStringSet(fcmd.CombinedOutputLog[1]...).HasAll("iptables", "-t", "nat", "-C", "OUTPUT", "abc", "123") {
 		t.Errorf("wrong CombinedOutput() log, got %s", fcmd.CombinedOutputLog[0])
 	}
 }
@@ -244,6 +264,8 @@ func TestDeleteRuleAlreadyExists(t *testing.T) {
 func TestDeleteRuleNew(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Success on the first call.
 			func() ([]byte, error) { return []byte{}, nil },
 			// Success on the second call.
@@ -252,7 +274,9 @@ func TestDeleteRuleNew(t *testing.T) {
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Success of that means delete it.
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Success of that means delete it.
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
@@ -262,10 +286,10 @@ func TestDeleteRuleNew(t *testing.T) {
 	if err != nil {
 		t.Errorf("expected success, got %+v", err)
 	}
-	if fcmd.CombinedOutputCalls != 2 {
-		t.Errorf("expected 2 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 3 {
+		t.Errorf("expected 3 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
 	}
-	if !util.NewStringSet(fcmd.CombinedOutputLog[1]...).HasAll("iptables", "-t", "nat", "-D", "OUTPUT", "abc", "123") {
+	if !util.NewStringSet(fcmd.CombinedOutputLog[2]...).HasAll("iptables", "-t", "nat", "-D", "OUTPUT", "abc", "123") {
 		t.Errorf("wrong CombinedOutput() log, got %s", fcmd.CombinedOutputLog[1])
 	}
 }
@@ -273,13 +297,17 @@ func TestDeleteRuleNew(t *testing.T) {
 func TestDeleteRuleErrorChecking(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Status 2 on the first call.
 			func() ([]byte, error) { return nil, &exec.FakeExitError{2} },
 		},
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Failure of that means create it.
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Failure of that means create it.
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
 	}
@@ -288,14 +316,16 @@ func TestDeleteRuleErrorChecking(t *testing.T) {
 	if err == nil {
 		t.Errorf("expected failure")
 	}
-	if fcmd.CombinedOutputCalls != 1 {
-		t.Errorf("expected 1 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 2 {
+		t.Errorf("expected 2 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
 	}
 }
 
 func TestDeleteRuleErrorCreating(t *testing.T) {
 	fcmd := exec.FakeCmd{
 		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// iptables version check
+			func() ([]byte, error) { return []byte("iptables v1.9.22"), nil },
 			// Success on the first call.
 			func() ([]byte, error) { return []byte{}, nil },
 			// Status 1 on the second call.
@@ -304,7 +334,9 @@ func TestDeleteRuleErrorCreating(t *testing.T) {
 	}
 	fexec := exec.FakeExec{
 		CommandScript: []exec.FakeCommandAction{
-			// The first Command() call is checking the rule.  Success of that means delete it.
+			// iptables version check
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			// The second Command() call is checking the rule.  Success of that means delete it.
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
 		},
@@ -314,7 +346,176 @@ func TestDeleteRuleErrorCreating(t *testing.T) {
 	if err == nil {
 		t.Errorf("expected failure")
 	}
-	if fcmd.CombinedOutputCalls != 2 {
-		t.Errorf("expected 2 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
+	if fcmd.CombinedOutputCalls != 3 {
+		t.Errorf("expected 3 CombinedOutput() calls, got %d", fcmd.CombinedOutputCalls)
+	}
+}
+
+func TestGetIptablesHasCheckCommand(t *testing.T) {
+	testCases := []struct {
+		Version  string
+		Err      bool
+		Expected bool
+	}{
+		{"iptables v1.4.7", false, false},
+		{"iptables v1.4.11", false, true},
+		{"iptables v1.4.19.1", false, true},
+		{"iptables v2.0.0", false, true},
+		{"total junk", true, false},
+	}
+
+	for _, testCase := range testCases {
+		fcmd := exec.FakeCmd{
+			CombinedOutputScript: []exec.FakeCombinedOutputAction{
+				func() ([]byte, error) { return []byte(testCase.Version), nil },
+			},
+		}
+		fexec := exec.FakeExec{
+			CommandScript: []exec.FakeCommandAction{
+				func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+			},
+		}
+		check, err := getIptablesHasCheckCommand(&fexec)
+		if (err != nil) != testCase.Err {
+			t.Errorf("Expected error: %v, Got error: %v", testCase.Err, err)
+		}
+		if err == nil && testCase.Expected != check {
+			t.Errorf("Expected result: %v, Got result: %v")
+		}
+	}
+}
+
+func TestExtractIptablesVersion(t *testing.T) {
+	testCases := []struct {
+		Version string
+		V1      int
+		V2      int
+		V3      int
+		Err     bool
+	}{
+		{"iptables v1.4.7", 1, 4, 7, false},
+		{"iptables v1.4.11", 1, 4, 11, false},
+		{"iptables v0.2.5", 0, 2, 5, false},
+		{"iptables v1.2.3.4.5.6", 1, 2, 3, false},
+		{"iptables v1.4", 0, 0, 0, true},
+		{"iptables v12345.12345.12345.12344", 12345, 12345, 12345, false},
+		{"total junk", 0, 0, 0, true},
+	}
+
+	for _, testCase := range testCases {
+		v1, v2, v3, err := extractIptablesVersion(testCase.Version)
+		if (err != nil) != testCase.Err {
+			t.Errorf("Expected error: %v, Got error: %v", testCase.Err, err)
+		}
+		if err == nil {
+			if v1 != testCase.V1 {
+				t.Errorf("First version number incorrect for string \"%s\", got %d, expected %d", testCase.Version, v1, testCase.V1)
+			}
+			if v2 != testCase.V2 {
+				t.Errorf("Second version number incorrect for string \"%s\", got %d, expected %d", testCase.Version, v2, testCase.V2)
+			}
+			if v3 != testCase.V3 {
+				t.Errorf("Third version number incorrect for string \"%s\", got %d, expected %d", testCase.Version, v3, testCase.V3)
+			}
+		}
+	}
+}
+
+func TestIptablesHasCheckCommand(t *testing.T) {
+	testCases := []struct {
+		V1     int
+		V2     int
+		V3     int
+		Result bool
+	}{
+		{0, 55, 55, false},
+		{1, 0, 55, false},
+		{1, 4, 10, false},
+		{1, 4, 11, true},
+		{1, 4, 19, true},
+		{1, 5, 0, true},
+		{2, 0, 0, true},
+	}
+
+	for _, testCase := range testCases {
+		if result := iptablesHasCheckCommand(testCase.V1, testCase.V2, testCase.V3); result != testCase.Result {
+			t.Errorf("For %d.%d.%d expected %v got %v", testCase.V1, testCase.V2, testCase.V3, testCase.Result, result)
+		}
+	}
+}
+
+func TestCheckRuleWithoutCheckPresent(t *testing.T) {
+	iptables_save_output := `# Generated by iptables-save v1.4.7 on Wed Oct 29 14:56:01 2014
+*nat
+:PREROUTING ACCEPT [2136997:197881818]
+:POSTROUTING ACCEPT [4284525:258542680]
+:OUTPUT ACCEPT [5901660:357267963]
+-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER 
+COMMIT
+# Completed on Wed Oct 29 14:56:01 2014`
+
+	fcmd := exec.FakeCmd{
+		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// Success.
+			func() ([]byte, error) { return []byte(iptables_save_output), nil },
+		},
+	}
+	fexec := exec.FakeExec{
+		CommandScript: []exec.FakeCommandAction{
+			// The first Command() call is checking the rule.  Success of that exec means "done".
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+		},
+	}
+	runner := &runner{exec: &fexec}
+	exists, err := runner.checkRuleWithoutCheck(TableNAT, ChainPrerouting, "-m", "addrtype", "-j", "DOCKER", "--dst-type", "LOCAL")
+	if err != nil {
+		t.Errorf("expected success, got %+v", err)
+	}
+	if !exists {
+		t.Errorf("expected exists = true")
+	}
+	if fcmd.CombinedOutputCalls != 1 {
+		t.Errorf("expected 1 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
+	}
+	if !util.NewStringSet(fcmd.CombinedOutputLog[0]...).HasAll("iptables-save", "-t", "nat") {
+		t.Errorf("wrong CombinedOutput() log, got %s", fcmd.CombinedOutputLog[0])
+	}
+}
+
+func TestCheckRuleWithoutCheckAbsent(t *testing.T) {
+	iptables_save_output := `# Generated by iptables-save v1.4.7 on Wed Oct 29 14:56:01 2014
+*nat
+:PREROUTING ACCEPT [2136997:197881818]
+:POSTROUTING ACCEPT [4284525:258542680]
+:OUTPUT ACCEPT [5901660:357267963]
+-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER 
+COMMIT
+# Completed on Wed Oct 29 14:56:01 2014`
+
+	fcmd := exec.FakeCmd{
+		CombinedOutputScript: []exec.FakeCombinedOutputAction{
+			// Success.
+			func() ([]byte, error) { return []byte(iptables_save_output), nil },
+		},
+	}
+	fexec := exec.FakeExec{
+		CommandScript: []exec.FakeCommandAction{
+			// The first Command() call is checking the rule.  Success of that exec means "done".
+			func(cmd string, args ...string) exec.Cmd { return exec.InitFakeCmd(&fcmd, cmd, args...) },
+		},
+	}
+	runner := &runner{exec: &fexec}
+	exists, err := runner.checkRuleWithoutCheck(TableNAT, ChainPrerouting, "-m", "addrtype", "-j", "DOCKER")
+	if err != nil {
+		t.Errorf("expected success, got %+v", err)
+	}
+	if exists {
+		t.Errorf("expected exists = false")
+	}
+	if fcmd.CombinedOutputCalls != 1 {
+		t.Errorf("expected 1 CombinedOutput() call, got %d", fcmd.CombinedOutputCalls)
+	}
+	if !util.NewStringSet(fcmd.CombinedOutputLog[0]...).HasAll("iptables-save", "-t", "nat") {
+		t.Errorf("wrong CombinedOutput() log, got %s", fcmd.CombinedOutputLog[0])
 	}
 }