diff --git a/config/config.go b/config/config.go
index 07dc01af3..63e5cee7a 100644
--- a/config/config.go
+++ b/config/config.go
@@ -165,7 +165,7 @@ type configFlags struct {
 	DropAddrIndex        bool          `long:"dropaddrindex" description:"Deletes the address-based transaction index from the database on start up and then exits."`
 	RelayNonStd          bool          `long:"relaynonstd" description:"Relay non-standard transactions regardless of the default settings for the active network."`
 	RejectNonStd         bool          `long:"rejectnonstd" description:"Reject non-standard transactions regardless of the default settings for the active network."`
-	SubNetwork           uint64        `long:"subnetwork" description:"If subnetwork > 0, than node will request and process only payloads from specified subnetwork. And if subnetwork is 0, than payloads of all subnetworks are processed."`
+	SubNetwork           uint64        `long:"subnetwork" description:"If subnetwork > 0, than node will request and process only payloads from specified subnetwork. And if subnetwork is 0, than payloads of all subnetworks are processed. Subnetworks 3 through 255 are reserved for future use and are currently not allowed."`
 }
 
 // Config defines the configuration options for btcd.
@@ -751,8 +751,16 @@ func loadConfig() (*Config, []string, error) {
 		cfg.MiningAddrs = append(cfg.MiningAddrs, addr)
 	}
 
+	if cfg.SubNetwork >= wire.SubNetworkReservedFirst && cfg.SubNetwork <= wire.SubNetworkReservedLast {
+		str := "%s: subnetworkID %d is reserved for future use, and nodes can not run in it "
+		err := fmt.Errorf(str, funcName, cfg.SubNetwork)
+		fmt.Fprintln(os.Stderr, err)
+		fmt.Fprintln(os.Stderr, usageMessage)
+		return nil, nil, err
+	}
+
 	// Check that 'generate' and 'subnetwork' flags do not conflict
-	if cfg.Generate && cfg.SubNetwork != 0 {
+	if cfg.Generate && cfg.SubNetwork != wire.SubNetworkSupportsAll {
 		str := "%s: both generate flag and subnetwork filtering are set "
 		err := fmt.Errorf(str, funcName)
 		fmt.Fprintln(os.Stderr, err)
diff --git a/config/config_test.go b/config/config_test.go
index 918924ef2..da9240561 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -7,6 +7,8 @@ import (
 	"regexp"
 	"runtime"
 	"testing"
+
+	"github.com/daglabs/btcd/wire"
 )
 
 var (
@@ -70,3 +72,18 @@ func TestCreateDefaultConfigFile(t *testing.T) {
 		t.Error("Could not find rpcpass in generated default config file.")
 	}
 }
+
+// TestConstants makes sure that all constants hard-coded into the help text were not modified.
+func TestConstants(t *testing.T) {
+	if wire.SubNetworkSupportsAll != 0 {
+		t.Errorf("wire.SubNetworkSupportsAll value was changed from 0, therefore you probably need to update the help text for SubNetwork")
+	}
+
+	if wire.SubNetworkReservedFirst != 3 {
+		t.Errorf("wire.SubNetworkReservedFirst value was changed from 0, therefore you probably need to update the help text for SubNetwork")
+	}
+
+	if wire.SubNetworkReservedLast != 255 {
+		t.Errorf("wire.SubNetworkReservedLast value was changed from 0, therefore you probably need to update the help text for SubNetwork")
+	}
+}
diff --git a/wire/msgtx.go b/wire/msgtx.go
index 682fcd717..957c3b994 100644
--- a/wire/msgtx.go
+++ b/wire/msgtx.go
@@ -96,14 +96,21 @@ const (
 	// 6,400,000 bytes.
 	freeListMaxItems = 12500
 
-	// SubNetworkSupportsAll is the sub network id that is used to signal to peers that you support all sub-networks
+	// SubNetworkSupportsAll is the sub-network id that is used to signal to peers that you support all sub-networks
 	SubNetworkSupportsAll = 0
 
-	// SubNetworkDAGCoin is the default sub network which is used for transactions without related payload data
+	// SubNetworkDAGCoin is the default sub-network which is used for transactions without related payload data
 	SubNetworkDAGCoin = 1
 
-	// SubNetworkRegistry is the sub network which is used for adding new sub networks to the registry
+	// SubNetworkRegistry is the sub-network which is used for adding new sub networks to the registry
 	SubNetworkRegistry = 2
+
+	// SubNetworkReservedFirst and SubnetworkReservedLast mark the range of sub-networks that are reserved for future use
+	// and are currently un-assigned for anything
+	// SubNetworkReservedFirst is the first reserved sub-network
+	SubNetworkReservedFirst = 3
+	// SubNetworkReservedLast is the last reserved sub-network
+	SubNetworkReservedLast = 255
 )
 
 // scriptFreeList defines a free list of byte slices (up to the maximum number