From 8935ef0e31f6be7048f243204107829686656184 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Wed, 4 Dec 2002 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 2002-12-04

---
 ip/icmp.c | 18 +++++++++++++++---
 ip/ip.c   |  3 +++
 ip/ip.h   |  1 +
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/ip/icmp.c b/ip/icmp.c
index 52e2a65446c092cd5682e557c8b8abf7d4cec93a..026ca674303d819c1131acb26a290f8a3e57e4ed 100644
--- a/ip/icmp.c
+++ b/ip/icmp.c
@@ -215,8 +215,8 @@ icmpttlexceeded(Fs *f, uchar *ia, Block *bp)
 
 }
 
-extern void
-icmpnoconv(Fs *f, Block *bp)
+static void
+icmpunreachable(Fs *f, Block *bp, int code)
 {
 	Block	*nbp;
 	Icmp	*p, *np;
@@ -244,7 +244,7 @@ icmpnoconv(Fs *f, Block *bp)
 	memmove(np->src, p->dst, sizeof(np->src));
 	memmove(np->data, bp->rp, ICMP_IPSIZE + 8);
 	np->type = Unreachable;
-	np->code = 3;
+	np->code = code;
 	np->proto = IP_ICMPPROTO;
 	hnputs(np->icmpid, 0);
 	hnputs(np->seq, 0);
@@ -253,6 +253,18 @@ icmpnoconv(Fs *f, Block *bp)
 	ipoput4(f, nbp, 0, MAXTTL, DFLTTOS);
 }
 
+extern void
+icmpnoconv(Fs *f, Block *bp)
+{
+	icmpunreachable(f, bp, 3);
+}
+
+extern void
+icmpcantfrag(Fs *f, Block *bp)
+{
+	icmpunreachable(f, bp, 4);
+}
+
 static void
 goticmpkt(Proto *icmp, Block *bp)
 {
diff --git a/ip/ip.c b/ip/ip.c
index 18b68fe763d520d2b7bd42fa2338743c716ae865..5c486619af40c783e5c2e5881ae4484fa526b45b 100644
--- a/ip/ip.c
+++ b/ip/ip.c
@@ -312,9 +312,12 @@ ipoput4(Fs *f, Block *bp, int gating, int ttl, int tos)
 		return;
 	}
 
+if((eh->frag[0] & (IP_DF>>8)) && !gating) print("%V: DF set\n", eh->dst);
+
 	if(eh->frag[0] & (IP_DF>>8)){
 		ip->stats[FragFails]++;
 		ip->stats[OutDiscards]++;
+		icmpcantfrag(f, bp);
 		netlog(f, Logip, "%V: eh->frag[0] & (IP_DF>>8)\n", eh->dst);
 		goto raise;
 	}
diff --git a/ip/ip.h b/ip/ip.h
index bf0f78afe09a81b14269627e766a609dd0182237..f20092a8c4eecb2cddfa769ef4f7ea7574dc6758 100644
--- a/ip/ip.h
+++ b/ip/ip.h
@@ -614,6 +614,7 @@ extern long	ipgateread6(Fs *f, char *cp, ulong offset, int n);
 extern void	iprouting(Fs*, int);
 extern void	closeifcconv(Ifcconv*);
 extern void	icmpnoconv(Fs*, Block*);
+extern void	icmpcantfrag(Fs*, Block*);
 extern void	icmpttlexceeded(Fs*, uchar*, Block*);
 extern ushort	ipcsum(uchar*);
 extern void	ipiput4(Fs*, Ipifc*, Block*);