I've been running with these changes for a long time.
The change to icmp6.c just corrects packet counts.
The changes to il.c were jmk's suggestion to avoid
exhausting the supply of rpc mount buffers.

Reference: /n/sources/patch/applied/ip-fixes
Date: Tue Dec 13 03:29:20 CET 2005

--- /sys/src/9/ip/icmp6.c	Tue Dec 13 03:27:22 2005
+++ /sys/src/9/ip/icmp6.c	Tue Dec 13 03:27:18 2005
@@ -337,7 +337,7 @@
  * sends out an ICMPv6 neighbor solicitation
  * 	suni == SRC_UNSPEC or SRC_UNI, 
  *	tuni == TARG_MULTI => multicast for address resolution,
- * 	and tflag == TARG_UNI => neighbor reachability.
+ * 	and tuni == TARG_UNI => neighbor reachability.
  */
 
 extern void
@@ -831,7 +831,6 @@
 			freeblist(bp);
 		}
 
-		ipriv->out[NbrSolicit]++;
 		break;
 
 	case NbrAdvert:
--- /sys/src/9/ip/il.c	Tue Dec 13 03:27:37 2005
+++ /sys/src/9/ip/il.c	Tue Dec 13 03:27:32 2005
@@ -70,6 +70,8 @@
 
 	DefByteRate	= 100,		/* assume a megabit link */
 	DefRtt		= 50,		/* cross country on a great day */
+
+	Maxrq		= 64*1024,
 };
 
 enum
@@ -163,6 +165,7 @@
 	Retrans,		/* retransmissions */
 	DupMsg,
 	DupBytes,
+	DroppedMsgs,
 
 	Nstats,
 };
@@ -178,6 +181,7 @@
 [Retrans]	"Retrans",
 [DupMsg]	"DupMsg",
 [DupBytes]	"DupBytes",
+[DroppedMsgs]	"DroppedMsgs",
 };
 
 typedef struct Ilpriv Ilpriv;
@@ -415,7 +419,7 @@
 static void
 ilcreate(Conv *c)
 {
-	c->rq = qopen(64*1024, 0, 0, c);
+	c->rq = qopen(Maxrq, 0, 0, c);
 	c->wq = qbypass(ilkick, c);
 }
 
@@ -722,6 +726,17 @@
 			freeblist(bp);	
 			break;
 		case Ildata:
+			/*
+			 * avoid consuming all the mount rpc buffers in the
+			 * system.  if the input queue is too long, drop this
+			 * packet.
+			 */
+			if (s->rq && qlen(s->rq) >= Maxrq) {
+				priv->stats[DroppedMsgs]++;
+				freeblist(bp);
+				break;
+			}
+
 			ilackto(ic, ack, bp);
 			iloutoforder(s, h, bp);
 			ilpullup(s);
@@ -912,7 +927,7 @@
 		bp = packblock(bp);
 		if(bp == 0)
 			panic("ilpullup2");
-		qpassnolim(s->rq, bp);
+		qpass(s->rq, bp);
 	}
 	qunlock(&ic->outo);
 }