diff -Naur libpcap-1.3.0/bpf/net/bpf_filter.c libpcap-1.3.0-with-modulus/bpf/net/bpf_filter.c
--- libpcap-1.3.0/bpf/net/bpf_filter.c	2012-03-29 12:57:32.000000000 +0000
+++ libpcap-1.3.0-with-modulus/bpf/net/bpf_filter.c	2012-08-31 01:36:53.206825554 +0000
@@ -469,6 +469,12 @@
 			A /= X;
 			continue;
 
+		case BPF_ALU|BPF_MOD|BPF_X:
+			if (X == 0)
+				return 0;
+			A %= X;
+			continue;
+
 		case BPF_ALU|BPF_AND|BPF_X:
 			A &= X;
 			continue;
@@ -501,6 +507,10 @@
 			A /= pc->k;
 			continue;
 
+		case BPF_ALU|BPF_MOD|BPF_K:
+			A %= pc->k;
+			continue;
+
 		case BPF_ALU|BPF_AND|BPF_K:
 			A &= pc->k;
 			continue;
@@ -621,6 +631,13 @@
 				 */
 				if (BPF_SRC(p->code) == BPF_K && p->k == 0)
 					return 0;
+				break;
+			case BPF_MOD:
+				/*
+				 * Check for illegal modulus 0.
+				 */
+				if (BPF_SRC(p->code) == BPF_K && p->k == 0)
+					return 0;
 				break;
 			default:
 				return 0;
diff -Naur libpcap-1.3.0/bpf_image.c libpcap-1.3.0-with-modulus/bpf_image.c
--- libpcap-1.3.0/bpf_image.c	2012-03-29 12:57:32.000000000 +0000
+++ libpcap-1.3.0-with-modulus/bpf_image.c	2012-08-31 01:36:53.225825770 +0000
@@ -216,6 +216,11 @@
 		fmt = "x";
 		break;
 
+	case BPF_ALU|BPF_MOD|BPF_X:
+		op = "mod";
+		fmt = "x";
+		break;
+
 	case BPF_ALU|BPF_AND|BPF_X:
 		op = "and";
 		fmt = "x";
@@ -256,6 +261,11 @@
 		fmt = "#%d";
 		break;
 
+	case BPF_ALU|BPF_MOD|BPF_K:
+		op = "mod";
+		fmt = "#%d";
+		break;
+
 	case BPF_ALU|BPF_AND|BPF_K:
 		op = "and";
 		fmt = "#0x%x";
diff -Naur libpcap-1.3.0/grammar.y libpcap-1.3.0-with-modulus/grammar.y
--- libpcap-1.3.0/grammar.y	2012-03-29 12:57:32.000000000 +0000
+++ libpcap-1.3.0-with-modulus/grammar.y	2012-08-31 01:36:53.196825439 +0000
@@ -617,6 +617,7 @@
 	| arth '*' arth			{ $$ = gen_arth(BPF_MUL, $1, $3); }
 	| arth '/' arth			{ $$ = gen_arth(BPF_DIV, $1, $3); }
 	| arth '&' arth			{ $$ = gen_arth(BPF_AND, $1, $3); }
+	| arth '%' arth			{ $$ = gen_arth(BPF_MOD, $1, $3); }
 	| arth '|' arth			{ $$ = gen_arth(BPF_OR, $1, $3); }
 	| arth LSH arth			{ $$ = gen_arth(BPF_LSH, $1, $3); }
 	| arth RSH arth			{ $$ = gen_arth(BPF_RSH, $1, $3); }
diff -Naur libpcap-1.3.0/optimize.c libpcap-1.3.0-with-modulus/optimize.c
--- libpcap-1.3.0/optimize.c	2012-03-29 12:57:32.000000000 +0000
+++ libpcap-1.3.0-with-modulus/optimize.c	2012-08-31 01:36:53.188825347 +0000
@@ -666,6 +666,12 @@
 		a /= b;
 		break;
 
+	case BPF_MOD:
+		if (b == 0)
+			bpf_error("illegal modulus 0");
+		a %= b;
+		break;
+
 	case BPF_AND:
 		a &= b;
 		break;
@@ -1044,6 +1050,7 @@
 	case BPF_ALU|BPF_SUB|BPF_K:
 	case BPF_ALU|BPF_MUL|BPF_K:
 	case BPF_ALU|BPF_DIV|BPF_K:
+	case BPF_ALU|BPF_MOD|BPF_K:
 	case BPF_ALU|BPF_AND|BPF_K:
 	case BPF_ALU|BPF_OR|BPF_K:
 	case BPF_ALU|BPF_LSH|BPF_K:
@@ -1079,6 +1086,7 @@
 	case BPF_ALU|BPF_SUB|BPF_X:
 	case BPF_ALU|BPF_MUL|BPF_X:
 	case BPF_ALU|BPF_DIV|BPF_X:
+	case BPF_ALU|BPF_MOD|BPF_X:
 	case BPF_ALU|BPF_AND|BPF_X:
 	case BPF_ALU|BPF_OR|BPF_X:
 	case BPF_ALU|BPF_LSH|BPF_X:
@@ -1112,7 +1120,7 @@
 				vstore(s, &val[A_ATOM], val[X_ATOM], alter);
 				break;
 			}
-			else if (op == BPF_MUL || op == BPF_DIV ||
+			else if (op == BPF_MUL || op == BPF_DIV || op == BPF_MOD ||
 				 op == BPF_AND || op == BPF_LSH || op == BPF_RSH) {
 				s->code = BPF_LD|BPF_IMM;
 				s->k = 0;
diff -Naur libpcap-1.3.0/pcap/bpf.h libpcap-1.3.0-with-modulus/pcap/bpf.h
--- libpcap-1.3.0/pcap/bpf.h	2012-06-12 16:55:36.000000000 +0000
+++ libpcap-1.3.0-with-modulus/pcap/bpf.h	2012-08-31 01:36:53.199825471 +0000
@@ -1235,6 +1235,7 @@
 #define		BPF_LSH		0x60
 #define		BPF_RSH		0x70
 #define		BPF_NEG		0x80
+#define		BPF_MOD		0x90
 #define		BPF_JA		0x00
 #define		BPF_JEQ		0x10
 #define		BPF_JGT		0x20
diff -Naur libpcap-1.3.0/scanner.l libpcap-1.3.0-with-modulus/scanner.l
--- libpcap-1.3.0/scanner.l	2012-03-29 12:57:32.000000000 +0000
+++ libpcap-1.3.0-with-modulus/scanner.l	2012-08-31 01:36:53.225825770 +0000
@@ -329,7 +329,7 @@
 sls		return SLS;
 
 [ \r\n\t]		;
-[+\-*/:\[\]!<>()&|=]	return yytext[0];
+[+\-*/:\[\]!<>()&|=%]	return yytext[0];
 ">="			return GEQ;
 "<="			return LEQ;
 "!="			return NEQ;
@@ -387,7 +387,7 @@
 [A-Za-z0-9]([-_.A-Za-z0-9]*[.A-Za-z0-9])? {
 			 yylval.s = sdup((char *)yytext); return ID; }
 "\\"[^ !()\n\t]+	{ yylval.s = sdup((char *)yytext + 1); return ID; }
-[^ \[\]\t\n\-_.A-Za-z0-9!<>()&|=]+ {
+[^ \[\]\t\n\-_.A-Za-z0-9!<>()&|=%]+ {
 			bpf_error("illegal token: %s", yytext); }
 .			{ bpf_error("illegal char '%c'", *yytext); }
 %%