diff --git a/filter/config.Y b/filter/config.Y
index 856189ec..ed94b9bf 100644
--- a/filter/config.Y
+++ b/filter/config.Y
@@ -34,16 +34,15 @@ CF_KEYWORDS(FUNCTION, PRINT, PRINTN, CONST, UNSET, RETURN,
 	INT, BOOL, IP, PREFIX, PAIR, SET, STRING,
 	IF, THEN, ELSE, CASE,
 	TRUE, FALSE,
-	RTA, FROM, GW, NET, MASK, RIP_METRIC, RIP_TAG, SOURCE,
+	FROM, GW, NET, MASK, SOURCE,
 	LEN,
 	DEFINED,
-	IMPOSSIBLE,
 	FILTER, WHERE)
 
 %nonassoc THEN
 %nonassoc ELSE
 
-%type <x> term block cmds cmd function_body constant print_one print_list var_list var_listn any_dynamic function_call
+%type <x> term block cmds cmd function_body constant print_one print_list var_list var_listn dynamic_attr function_call
 %type <f> filter filter_body where_filter
 %type <i> type break_command pair
 %type <e> set_item set_items switch_body
@@ -268,10 +267,12 @@ constant:
  | ENUM	  { $$ = f_new_inst(); $$->code = 'c'; $$->aux = $1 >> 16; $$->a2.i = $1 & 0xffff; }
  ;
 
-any_dynamic:
-   RIP_METRIC { $$ = f_new_inst(); $$->aux = T_INT; $$->a2.i = EA_RIP_METRIC;}
- | RIP_TAG    { $$ = f_new_inst(); $$->aux = T_INT; $$->a2.i = EA_RIP_TAG; }
- ;
+/*
+ *  Maybe there are no dynamic attributes defined by protocols.
+ *  For such cases, we force the dynamic_attr list to contain
+ *  at least an invalid token, so it's syntantically correct.
+ */
+CF_ADDTO(dynamic_attr, INVALID_TOKEN { $$ = NULL; })
 
 rtadot: /* EMPTY, we are not permitted RTA. prefix */
  ;
@@ -334,7 +335,7 @@ term:
  | rtadot NET     { $$ = f_new_inst(); $$->code = 'a'; $$->aux = T_PREFIX; $$->a2.i = 0x12345678; }
  | rtadot SOURCE  { $$ = f_new_inst(); $$->code = 'a'; $$->aux = T_ENUM_RTS; $$->a2.i = OFFSETOF(struct rta, gw); }
 
- | rtadot any_dynamic { $$ = $2; $$->code = P('e','a'); }
+ | rtadot dynamic_attr { $$ = $2; $$->code = P('e','a'); }
 
  | term '.' IP { $$ = f_new_inst(); $$->code = P('c','p'); $$->a1.p = $1; $$->aux = T_IP; }
  | term '.' LEN { $$ = f_new_inst(); $$->code = P('c','p'); $$->a1.p = $1; $$->aux = T_INT; }
@@ -416,12 +417,12 @@ cmd:
      $$->code = 'r';
      $$->a1.p = $2;
    }
- | rtadot any_dynamic '=' term ';' {
+ | rtadot dynamic_attr '=' term ';' {
      $$ = $2;
      $$->code  = P('e','S');
      $$->a1.p = $4;
    }
- | UNSET '(' rtadot any_dynamic ')' ';' {
+ | UNSET '(' rtadot dynamic_attr ')' ';' {
      $$ = $4;
      $$->aux = T_VOID;
      $$->code = P('e','S');
diff --git a/filter/f-util.c b/filter/f-util.c
index b070d951..2bc78737 100644
--- a/filter/f-util.c
+++ b/filter/f-util.c
@@ -32,6 +32,15 @@ f_new_inst(void)
   return ret;
 }
 
+struct f_inst *
+f_new_dynamic_attr(int code)
+{
+  struct f_inst *f = f_new_inst();
+  f->aux = T_INT;
+  f->a2.i = code;
+  return f;
+}
+
 char *
 filter_name(struct filter *filter)
 {
diff --git a/filter/filter.h b/filter/filter.h
index a08f1267..bbf30408 100644
--- a/filter/filter.h
+++ b/filter/filter.h
@@ -57,6 +57,7 @@ struct filter {
 
 void filters_postconfig(void);
 struct f_inst *f_new_inst(void);
+struct f_inst *f_new_dynamic_attr(int code);
 struct f_tree *f_new_tree(void);
 
 struct f_tree *build_tree(struct f_tree *);
@@ -121,6 +122,4 @@ struct f_tree {
 
 #define NEW_F_VAL struct f_val * val; val = cfg_alloc(sizeof(struct f_val));
 
-/* Create pair from two letters */
-
 #endif
diff --git a/proto/rip/config.Y b/proto/rip/config.Y
index 1bc67207..e1094a50 100644
--- a/proto/rip/config.Y
+++ b/proto/rip/config.Y
@@ -25,7 +25,8 @@ CF_DECLS
 CF_KEYWORDS(RIP, INFINITY, METRIC, PORT, PERIOD, GARBAGETIME, PASSWORDS,
 	    MODE, BROADCAST, QUIET, NOLISTEN, VERSION1, 
 	    AUTHENTICATION, NONE, PLAINTEXT, MD5,
-	    HONOUR, NEVER, NEIGHBOUR, ALWAYS)
+	    HONOUR, NEVER, NEIGHBOUR, ALWAYS,
+	    RIP_METRIC, RIP_TAG)
 
 %type <i> rip_mode rip_auth
 
@@ -97,6 +98,9 @@ rip_iface_list:
  | rip_iface_list ',' rip_iface
  ;
 
+CF_ADDTO(dynamic_attr, RIP_METRIC { $$ = f_new_dynamic_attr(EA_RIP_METRIC); })
+CF_ADDTO(dynamic_attr, RIP_TAG { $$ = f_new_dynamic_attr(EA_RIP_TAG); })
+
 CF_CODE
 
 CF_END