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For completeness I figured I had to also make a similar modification
for IP_MULTICAST_LOOP. See attached diff.

On Sun, Sep 11, 2005 at 12:11:44AM +0200, Stoned Elipot wrote:
> Hi,
> I've been wondering why ntpd stopped working in my usual multicast
> setup since ntp 4.x import. Yes it had been quite some time since then :)
> 
> Anyway, ntpd in src/dist/ntp/ntpd/ntp_io.c sets the TTL of outgoing multicast
> packets via an int option value argument to setsockopt(), search for
> IP_MULTICAST_TTL in this source file... This fail because
> netinet/ip_output.c:ip_setmoptions() check that the option value
> for IP_MULTICAST_TTL is one byte long, it bails out otherwise.
> 
> Then I noticed that FreeBSD's code allows for an int type option value
> in the same situation, see the same fonction in the same source file of
> FreeBSD's kernel.
> 
> So instead of "fixing" ntpd's sources I had a try to make a similar change
> in NetBSD's ip_setmoptions().
> 
> The attached patch contains this change, I tested it successfully on
> i386 3.99.8 current and sparc64 2.0_STABLE.
> 
> I'd like to hear your opinions on this as I'd like to commit such a change.
> 
> Cheers, Stoned.

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Index: ip_output.c
===================================================================
RCS file: /cvsroot/src/sys/netinet/ip_output.c,v
retrieving revision 1.155
diff -u -r1.155 ip_output.c
--- ip_output.c	18 Aug 2005 00:30:59 -0000	1.155
+++ ip_output.c	11 Sep 2005 21:12:11 -0000
@@ -1702,11 +1702,21 @@
 		/*
 		 * Set the IP time-to-live for outgoing multicast packets.
 		 */
-		if (m == NULL || m->m_len != 1) {
+		if (m == NULL) {
 			error = EINVAL;
 			break;
 		}
-		imo->imo_multicast_ttl = *(mtod(m, u_char *));
+		if (m->m_len == 1)
+			imo->imo_multicast_ttl = *(mtod(m, u_char *));
+		else if (m->m_len == sizeof(unsigned int)) {
+			unsigned int uttl;
+			uttl = *(mtod(m, unsigned int *));
+			if (uttl > 255)
+				error = EINVAL;
+			else
+				imo->imo_multicast_ttl = (u_int8_t) uttl;
+		} else
+			error = EINVAL;
 		break;
 
 	case IP_MULTICAST_LOOP:
@@ -1714,8 +1724,19 @@
 		 * Set the loopback flag for outgoing multicast packets.
 		 * Must be zero or one.
 		 */
-		if (m == NULL || m->m_len != 1 ||
-		   (loop = *(mtod(m, u_char *))) > 1) {
+		if (m == NULL) {
+			error = EINVAL;
+			break;
+		}
+		if (m->m_len == 1)
+		   	loop = *(mtod(m, u_char *));
+		else if (m->m_len == sizeof(unsigned int))
+			loop = (u_char)*(mtod(m, unsigned int *));
+		else {
+			error = EINVAL;
+			break;
+		}
+		if (loop > 1) {
 			error = EINVAL;
 			break;
 		}

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