diff -uN linux.orig/net/ipv4/netfilter/ipt_NETMAP.c linux/net/ipv4/netfilter/ipt_NETMAP.c
--- linux.orig/net/ipv4/netfilter/ipt_NETMAP.c	Thu Jan  1 01:00:00 1970
+++ linux/net/ipv4/netfilter/ipt_NETMAP.c	Thu Apr 19 17:30:18 2001
@@ -0,0 +1,106 @@
+/* NETMAP - static NAT mapping of IP network addresses (1:1).
+   The mapping can be applied to source (POSTROUTING),
+   destination (PREROUTING), or both (with separate rules).
+
+   Author: Svenning Soerensen <svenning@post5.tele.dk>
+*/
+
+#include <linux/config.h>
+#include <linux/ip.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter_ipv4.h>
+#include <linux/netfilter_ipv4/ip_nat_rule.h>
+
+#define MODULENAME "NETMAP"
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+static int
+check(const char *tablename,
+      const struct ipt_entry *e,
+      void *targinfo,
+      unsigned int targinfosize,
+      unsigned int hook_mask)
+{
+	const struct ip_nat_multi_range *mr = targinfo;
+
+	if (strcmp(tablename, "nat") != 0) {
+		DEBUGP(MODULENAME":check: bad table `%s'.\n", tablename);
+		return 0;
+	}
+	if (targinfosize != IPT_ALIGN(sizeof(*mr))) {
+		DEBUGP(MODULENAME":check: size %u.\n", targinfosize);
+		return 0;
+	}
+	if (hook_mask & ~((1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING))) {
+		DEBUGP(MODULENAME":check: bad hooks %x.\n", hook_mask);
+		return 0;
+	}
+	if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
+		DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
+		return 0;
+	}
+	if (mr->rangesize != 1) {
+		DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
+		return 0;
+	}
+	return 1;
+}
+
+static unsigned int
+target(struct sk_buff **pskb,
+       unsigned int hooknum,
+       const struct net_device *in,
+       const struct net_device *out,
+       const void *targinfo,
+       void *userinfo)
+{
+	struct ip_conntrack *ct;
+	enum ip_conntrack_info ctinfo;
+	u_int32_t new_ip, netmask;
+	const struct ip_nat_multi_range *mr = targinfo;
+	struct ip_nat_multi_range newrange;
+
+	IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
+		     || hooknum == NF_IP_POST_ROUTING);
+	ct = ip_conntrack_get(*pskb, &ctinfo);
+
+	netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
+
+	if (hooknum == NF_IP_PRE_ROUTING)
+		new_ip = (*pskb)->nh.iph->daddr & ~netmask;
+	else
+		new_ip = (*pskb)->nh.iph->saddr & ~netmask;
+	new_ip |= mr->range[0].min_ip & netmask;
+
+	newrange = ((struct ip_nat_multi_range)
+	{ 1, { { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
+		 new_ip, new_ip,
+		 mr->range[0].min, mr->range[0].max } } });
+
+	/* Hand modified range to generic setup. */
+	return ip_nat_setup_info(ct, &newrange, hooknum);
+}
+
+static struct ipt_target target_module
+= { { NULL, NULL }, MODULENAME, target, check, NULL,
+    THIS_MODULE };
+
+static int __init init(void)
+{
+	return ipt_register_target(&target_module);
+}
+
+static void __exit fini(void)
+{
+	ipt_unregister_target(&target_module);
+}
+
+module_init(init);
+module_exit(fini);
