diff --git a/Shorewall/Perl/Shorewall/Chains.pm b/Shorewall/Perl/Shorewall/Chains.pm
index fdcadb5d4..7b170ecd6 100644
--- a/Shorewall/Perl/Shorewall/Chains.pm
+++ b/Shorewall/Perl/Shorewall/Chains.pm
@@ -2644,7 +2644,7 @@ sub mark_firewall_not_started() {
 # Returns the name of the shell variable holding the first address of the passed interface
 #
 sub interface_address( $ ) {
-    my $variable = chain_base( $_[0] ) . '_address';
+    my $variable = 'sw_' . chain_base( $_[0] ) . '_address';
     uc $variable;
 }
 
@@ -2669,7 +2669,7 @@ sub get_interface_address ( $ ) {
 # Returns the name of the shell variable holding the broadcast addresses of the passed interface
 #
 sub interface_bcasts( $ ) {
-    my $variable = chain_base( $_[0] ) . '_bcasts';
+    my $variable = 'sw_' . chain_base( $_[0] ) . '_bcasts';
     uc $variable;
 }
 
@@ -2692,7 +2692,7 @@ sub get_interface_bcasts ( $ ) {
 # Returns the name of the shell variable holding the anycast addresses of the passed interface
 #
 sub interface_acasts( $ ) {
-    my $variable = chain_base( $_[0] ) . '_acasts';
+    my $variable = 'sw_' . chain_base( $_[0] ) . '_acasts';
     uc $variable;
 }
 
@@ -2715,7 +2715,7 @@ sub get_interface_acasts ( $ ) {
 # Returns the name of the shell variable holding the gateway through the passed interface
 #
 sub interface_gateway( $ ) {
-    my $variable = chain_base( $_[0] ) . '_gateway';
+    my $variable = 'sw_' . chain_base( $_[0] ) . '_gateway';
     uc $variable;
 }
 
@@ -2747,7 +2747,7 @@ sub get_interface_gateway ( $ ) {
 # Returns the name of the shell variable holding the addresses of the passed interface
 #
 sub interface_addresses( $ ) {
-    my $variable = chain_base( $_[0] ) . '_addresses';
+    my $variable = 'sw_' . chain_base( $_[0] ) . '_addresses';
     uc $variable;
 }
 
@@ -2777,7 +2777,7 @@ sub get_interface_addresses ( $ ) {
 # Returns the name of the shell variable holding the networks routed out of the passed interface
 #
 sub interface_nets( $ ) {
-    my $variable = chain_base( $_[0] ) . '_networks';
+    my $variable = 'sw_' . chain_base( $_[0] ) . '_networks';
     uc $variable;
 }
 
@@ -2808,7 +2808,7 @@ sub get_interface_nets ( $ ) {
 # Returns the name of the shell variable holding the MAC address of the gateway for the passed provider out of the passed interface
 #
 sub interface_mac( $$ ) {
-    my $variable = join( '_' , chain_base( $_[0] ) , chain_base( $_[1] ) , 'mac' );
+    my $variable = join( '_' , 'sw' , chain_base( $_[0] ) , chain_base( $_[1] ) , 'mac' );
     uc $variable;
 }
 
diff --git a/Shorewall/Perl/Shorewall/Providers.pm b/Shorewall/Perl/Shorewall/Providers.pm
index 55f16ce0c..5a25df3bc 100644
--- a/Shorewall/Perl/Shorewall/Providers.pm
+++ b/Shorewall/Perl/Shorewall/Providers.pm
@@ -416,7 +416,7 @@ sub add_a_provider( ) {
 	start_provider( $table, $number, qq(if interface_is_usable $physical && [ -n "$variable" ]; then) );
     } else {
 	if ( $optional ) {
-	    start_provider( $table, $number, qq(if [ -n "\$${base}_IS_USABLE" ]; then) );
+	    start_provider( $table, $number, qq(if [ -n "\$SW_${base}_IS_USABLE" ]; then) );
 	} elsif ( $gatewaycase eq 'detect' ) {
 	    start_provider( $table, $number, qq(if interface_is_usable $physical && [ -n "$gateway" ]; then) );
 	} else {
@@ -543,7 +543,7 @@ sub add_a_provider( ) {
 sub start_new_if( $ ) {
     our $current_if = shift;
 
-    emit ( '', qq(if [ -n "\$${current_if}_IS_USABLE" ]; then) );
+    emit ( '', qq(if [ -n "\$SW_${current_if}_IS_USABLE" ]; then) );
     push_indent;
 }
   
@@ -871,9 +871,9 @@ sub handle_optional_interfaces() {
 		emit qq(if interface_is_usable $physical; then);
 	    }
 
-	    emit( "    ${base}_IS_USABLE=Yes" ,
+	    emit( "    SW_${base}_IS_USABLE=Yes" ,
 		  'else' ,
-		  "    ${base}_IS_USABLE=" ,
+		  "    SW_${base}_IS_USABLE=" ,
 		  'fi' );
 	}