>Number:         1648
>Category:       bin
>Synopsis:       changing the mtu is not possible with ifconfig
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people (Utility Bug People)
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Wed Oct 18 12:35:02 1995
>Last-Modified:
>Originator:     Matthias Pfaller
>Organization:
leo@dachau.marco.de			in real life: Matthias Pfaller
marco GmbH, 85221 Dachau, Germany	tel: +49 8131 516142
>Release:        951014
>Environment:
	
System: NetBSD robin 1.0A NetBSD 1.0A (ROBIN) #10: Thu Oct 12 10:34:15 MET 1995 leo@robin:/usr/src/sys/arch/i386/compile/ROBIN i386


>Description:
	Changing the MTU of an interface is not possible with ifconfig.
>How-To-Repeat:
>Fix:
The following patch allows ifconfig to change the MTU and documents the
new option.
--- ifconfig.8.orig	Fri Jun 23 13:48:52 1995
+++ ifconfig.8	Fri Jun 23 13:47:35 1995
@@ -176,6 +176,10 @@
 Higher metrics have the effect of making a route
 less favorable; metrics are counted as addition hops
 to the destination network or host.
+.It Cm mtu Ar n
+Set the maximum transmission unit of the interface to
+.Ar n .
+Most interfaces don't support this option.
 .It Cm netmask Ar mask
 (Inet and ISO)
 Specify how much of the address to reserve for subdividing
--- ifconfig.c.orig	Sat Oct 14 02:10:15 1995
+++ ifconfig.c	Wed Oct 18 17:09:36 1995
@@ -79,7 +79,7 @@
 struct	iso_aliasreq	iso_addreq;
 struct	sockaddr_in	netmask;
 char	name[30];
-int	flags, metric, setaddr, setipdst, doalias;
+int	flags, metric, mtu, setaddr, setipdst, doalias;
 int	clearaddr, s;
 int	newaddr = 1;
 int	nsellength = 1;
@@ -93,6 +93,7 @@
 void 	setifbroadaddr __P((char *));
 void 	setifipdst __P((char *));
 void 	setifmetric __P((char *));
+void 	setifmtu __P((char *));
 void 	setifnetmask __P((char *));
 void 	setnsellength __P((char *));
 void 	setsnpaoffset __P((char *));
@@ -311,6 +312,10 @@
 		metric = 0;
 	} else
 		metric = ifr->ifr_metric;
+	if (ioctl(s, SIOCGIFMTU, (caddr_t)ifr) < 0)
+		mtu = 0;
+	else
+		mtu = ifr->ifr_metric;
 	return (0);
 }
 
@@ -475,6 +480,8 @@
 	printb("flags", flags, IFFBITS);
 	if (metric)
 		printf(" metric %d", metric);
+	if (mtu)
+		printf(" mtu %d", mtu);
 	putchar('\n');
 	if ((p = afp) != NULL) {
 		(*p->af_status)(1);
@@ -746,6 +753,16 @@
 }
 
 void
+setifmtu(val)
+	char *val;
+{
+	strncpy(ifr.ifr_name, name, sizeof (ifr.ifr_name));
+	ifr.ifr_metric = atoi(val);
+	if (ioctl(s, SIOCSIFMTU, (caddr_t)&ifr) < 0)
+		warn("SIOCSIFMTU");
+}
+
+void
 setsnpaoffset(val)
 	char *val;
 {
@@ -785,10 +802,11 @@
 void
 usage()
 {
-	fprintf(stderr, "usage: ifconfig interface\n%s%s%s%s%s%s",
+	fprintf(stderr, "usage: ifconfig interface\n%s%s%s%s%s%s%s",
 		"\t[ af [ address [ dest_addr ] ] [ up ] [ down ] ",
 		"[ netmask mask ] ]\n",
 		"\t[ metric n ]\n",
+		"\t[ mtu n ]\n",
 		"\t[ arp | -arp ]\n",
 		"\t[ link0 | -link0 ] [ link1 | -link1 ] [ link2 | -link2 ]\n",
 		"       ifconfig -a [ af ]\n");
>Audit-Trail:
>Unformatted: