diff --git a/net/ipv4/xfrm4_output.c b/net/ipv4/xfrm4_output.c
new file mode 100644
index 0000000..af2392a
--- /dev/null
+++ b/net/ipv4/xfrm4_output.c
@@ -0,0 +1,141 @@
+/*
+ * xfrm4_output.c - Common IPsec encapsulation code for IPv4.
+ * Copyright (c) 2004 Herbert Xu <herbert@gondor.apana.org.au>
+ * 
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <net/inet_ecn.h>
+#include <net/ip.h>
+#include <net/xfrm.h>
+#include <net/icmp.h>
+
+/* Add encapsulation header.
+ *
+ * In transport mode, the IP header will be moved forward to make space
+ * for the encapsulation header.
+ *
+ * In tunnel mode, the top IP header will be constructed per RFC 2401.
+ * The following fields in it shall be filled in by x->type->output:
+ *	tot_len
+ *	check
+ *
+ * On exit, skb->h will be set to the start of the payload to be processed
+ * by x->type->output and skb->nh will be set to the top IP header.
+ */
+static void xfrm4_encap(struct sk_buff *skb)
+{
+	struct dst_entry *dst = skb->dst;
+	struct xfrm_state *x = dst->xfrm;
+	struct iphdr *iph, *top_iph;
+
+	iph = skb->nh.iph;
+	skb->h.ipiph = iph;
+
+	skb->nh.raw = skb_push(skb, x->props.header_len);
+	top_iph = skb->nh.iph;
+
+	if (!x->props.mode) {
+		skb->h.raw += iph->ihl*4;
+		memmove(top_iph, iph, iph->ihl*4);
+		return;
+	}
+
+	top_iph->ihl = 5;
+	top_iph->version = 4;
+
+	/* DS disclosed */
+	top_iph->tos = INET_ECN_encapsulate(iph->tos, iph->tos);
+	if (x->props.flags & XFRM_STATE_NOECN)
+		IP_ECN_clear(top_iph);
+
+	top_iph->frag_off = iph->frag_off & htons(IP_DF);
+	if (!top_iph->frag_off)
+		__ip_select_ident(top_iph, dst, 0);
+
+	top_iph->ttl = dst_metric(dst->child, RTAX_HOPLIMIT);
+
+	top_iph->saddr = x->props.saddr.a4;
+	top_iph->daddr = x->id.daddr.a4;
+	top_iph->protocol = IPPROTO_IPIP;
+
+	memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
+}
+
+static int xfrm4_tunnel_check_size(struct sk_buff *skb)
+{
+	int mtu, ret = 0;
+	struct dst_entry *dst;
+	struct iphdr *iph = skb->nh.iph;
+
+	if (IPCB(skb)->flags & IPSKB_XFRM_TUNNEL_SIZE)
+		goto out;
+
+	IPCB(skb)->flags |= IPSKB_XFRM_TUNNEL_SIZE;
+	
+	if (!(iph->frag_off & htons(IP_DF)) || skb->local_df)
+		goto out;
+
+	dst = skb->dst;
+	mtu = dst_mtu(dst);
+	if (skb->len > mtu) {
+		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
+		ret = -EMSGSIZE;
+	}
+out:
+	return ret;
+}
+
+int xfrm4_output(struct sk_buff *skb)
+{
+	struct dst_entry *dst = skb->dst;
+	struct xfrm_state *x = dst->xfrm;
+	int err;
+	
+	if (skb->ip_summed == CHECKSUM_HW) {
+		err = skb_checksum_help(skb, 0);
+		if (err)
+			goto error_nolock;
+	}
+
+	if (x->props.mode) {
+		err = xfrm4_tunnel_check_size(skb);
+		if (err)
+			goto error_nolock;
+	}
+
+	spin_lock_bh(&x->lock);
+	err = xfrm_state_check(x, skb);
+	if (err)
+		goto error;
+
+	xfrm4_encap(skb);
+
+	err = x->type->output(x, skb);
+	if (err)
+		goto error;
+
+	x->curlft.bytes += skb->len;
+	x->curlft.packets++;
+
+	spin_unlock_bh(&x->lock);
+	
+	if (!(skb->dst = dst_pop(dst))) {
+		err = -EHOSTUNREACH;
+		goto error_nolock;
+	}
+	err = NET_XMIT_BYPASS;
+
+out_exit:
+	return err;
+error:
+	spin_unlock_bh(&x->lock);
+error_nolock:
+	kfree_skb(skb);
+	goto out_exit;
+}