diff -Naur arpwatch-2.1a15.orig/arpwatch.8 arpwatch-2.1a15/arpwatch.8
--- arpwatch-2.1a15.orig/arpwatch.8	2006-12-11 13:00:39.000000000 +0300
+++ arpwatch-2.1a15/arpwatch.8	2006-12-11 13:00:55.000000000 +0300
@@ -110,6 +110,11 @@
 .br
 .ti +9
 [
+.B -D
+]
+.br
+.ti +9
+[
 .B -z
 .I ignorenet/ignoremask
 ]
@@ -240,6 +245,10 @@
 flags prevents arpwatch from sending reports by mail. (This feature comes from Debian).
 .LP
 The
+.B -D
+flag turns off reverse-DNS queries. This can speed up operations significantly.
+.LP
+The
 .B -z
 flag is used to set a range of ip addresses to ignore (such as a DHCP
 range). Netmask is specified as 255.255.128.0. (This feature comes from Debian).
diff -Naur arpwatch-2.1a15.orig/arpwatch.c arpwatch-2.1a15/arpwatch.c
--- arpwatch-2.1a15.orig/arpwatch.c	2006-12-11 13:00:39.000000000 +0300
+++ arpwatch-2.1a15/arpwatch.c	2006-12-11 13:00:55.000000000 +0300
@@ -198,6 +198,7 @@
 		"u:"
 		"R:"
 		"Q"
+		"D"
 		"z:"
 	;
 	char *tmpptr;
@@ -289,6 +290,10 @@
 			++quiet;
 			break;
 
+		case 'D':
+			++noreversedns;
+			break;
+
 		case 'z':
 			tmpptr = strtok(optarg, "/");
 			inet_aton(tmpptr, &ignore_net);
@@ -900,6 +905,7 @@
 		"[-u username] "
 		"[-R seconds ] "
 		"[-Q] "
+		"[-D] "
 		"[-z ignorenet/ignoremask] "
 		"\n"
 	;
diff -Naur arpwatch-2.1a15.orig/arpwatch.h arpwatch-2.1a15/arpwatch.h
--- arpwatch-2.1a15.orig/arpwatch.h	2006-12-11 13:00:39.000000000 +0300
+++ arpwatch-2.1a15/arpwatch.h	2006-12-11 13:00:55.000000000 +0300
@@ -17,6 +17,7 @@
 extern char *prog;
 
 extern int nonewstations; /* Turns off new-station reporting. */
+extern int noreversedns; /* Turns off reverse-dns. */
 
 #ifdef ETHER_HEADER_HAS_EA
 #define ESRC(ep) ((ep)->ether_shost.ether_addr_octet)
diff -Naur arpwatch-2.1a15.orig/dns.c arpwatch-2.1a15/dns.c
--- arpwatch-2.1a15.orig/dns.c	2000-10-14 05:50:52.000000000 +0400
+++ arpwatch-2.1a15/dns.c	2006-12-11 13:01:07.000000000 +0300
@@ -71,6 +71,8 @@
 } querybuf;
 #endif
 
+int noreversedns = 0;
+
 int
 gethinfo(register char *hostname, register char *cpu, register int cpulen,
     register char *os, register int oslen)
@@ -84,6 +86,9 @@
 	register int type, class, buflen, ancount, qdcount;
 	querybuf qbuf;
 
+	if (noreversedns)
+		return (0);
+
 	qb = &qbuf;
 	n = res_query(hostname, C_IN, T_HINFO, qb->buf, sizeof(qb->buf));
 	if (n < 0)
@@ -144,6 +149,9 @@
 	register int32_t options;
 	register struct hostent *hp;
 
+	if (noreversedns)
+		return (intoa(a));
+
 	options = _res.options;
 	_res.options |= RES_AAONLY;
 	_res.options &= ~(RES_DEFNAMES | RES_DNSRCH);