diff --git a/tailnet/service.go b/tailnet/service.go
new file mode 100644
index 0000000000..92140aa3f5
--- /dev/null
+++ b/tailnet/service.go
@@ -0,0 +1,47 @@
+package tailnet
+
+import (
+	"strconv"
+	"strings"
+
+	"golang.org/x/xerrors"
+)
+
+const (
+	CurrentMajor = 2
+	CurrentMinor = 0
+)
+
+var SupportedMajors = []int{2, 1}
+
+func ValidateVersion(version string) error {
+	parts := strings.Split(version, ".")
+	if len(parts) != 2 {
+		return xerrors.Errorf("invalid version string: %s", version)
+	}
+	major, err := strconv.Atoi(parts[0])
+	if err != nil {
+		return xerrors.Errorf("invalid major version: %s", version)
+	}
+	minor, err := strconv.Atoi(parts[1])
+	if err != nil {
+		return xerrors.Errorf("invalid minor version: %s", version)
+	}
+	if major > CurrentMajor {
+		return xerrors.Errorf("server is at version %d.%d, behind requested version %s",
+			CurrentMajor, CurrentMinor, version)
+	}
+	if major == CurrentMajor {
+		if minor > CurrentMinor {
+			return xerrors.Errorf("server is at version %d.%d, behind requested version %s",
+				CurrentMajor, CurrentMinor, version)
+		}
+		return nil
+	}
+	for _, mjr := range SupportedMajors {
+		if major == mjr {
+			return nil
+		}
+	}
+	return xerrors.Errorf("version %s is no longer supported", version)
+}
diff --git a/tailnet/service_test.go b/tailnet/service_test.go
new file mode 100644
index 0000000000..ffb0442aea
--- /dev/null
+++ b/tailnet/service_test.go
@@ -0,0 +1,74 @@
+package tailnet_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/tailnet"
+)
+
+func TestValidateVersion(t *testing.T) {
+	t.Parallel()
+	for _, tc := range []struct {
+		name      string
+		version   string
+		supported bool
+	}{
+		{
+			name:      "Current",
+			version:   fmt.Sprintf("%d.%d", tailnet.CurrentMajor, tailnet.CurrentMinor),
+			supported: true,
+		},
+		{
+			name:    "TooNewMinor",
+			version: fmt.Sprintf("%d.%d", tailnet.CurrentMajor, tailnet.CurrentMinor+1),
+		},
+		{
+			name:    "TooNewMajor",
+			version: fmt.Sprintf("%d.%d", tailnet.CurrentMajor+1, tailnet.CurrentMinor),
+		},
+		{
+			name:      "1.0",
+			version:   "1.0",
+			supported: true,
+		},
+		{
+			name:      "2.0",
+			version:   "2.0",
+			supported: true,
+		},
+		{
+			name:    "Malformed0",
+			version: "cats",
+		},
+		{
+			name:    "Malformed1",
+			version: "cats.dogs",
+		},
+		{
+			name:    "Malformed2",
+			version: "1.0.1",
+		},
+		{
+			name:    "Malformed3",
+			version: "11",
+		},
+		{
+			name:    "TooOld",
+			version: "0.8",
+		},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			err := tailnet.ValidateVersion(tc.version)
+			if tc.supported {
+				require.NoError(t, err)
+			} else {
+				require.Error(t, err)
+			}
+		})
+	}
+}