Add the "Monitor" interface flag.

Setting this flag on an ethernet interface blocks transmission of packets
and discards incoming packets after BPF processing.

This is useful if you want to monitor network trafic but not interact
with the network in question.

Sponsored by:	http://www.babeltech.dk

2 files changed, 13 insertions, 0 deletions

diff --git a/sbin/ifconfig/ifconfig.8 b/sbin/ifconfig/ifconfig.8
index 39761fbe5803..57468e974b34 100644
--- a/sbin/ifconfig/ifconfig.8
+++ b/sbin/ifconfig/ifconfig.8
@@ -504,6 +504,17 @@ for more information.
 .It Fl link Op Cm 0 No - Cm 2
 .Sm on
 Disable special processing at the link level with the specified interface.
+.It Cm monitor
+.Sm on
+Put the interface in monitor mode.
+No packets are transmitted and received packets are discarded after
+.Xr bpf 4
+processing.
+.Sm off
+.It Fl monitor
+.Sm on
+Take the interface out of monitor mode.
+.Sm off
 .It Cm up
 Mark an interface
 .Dq up .
diff --git a/sbin/ifconfig/ifconfig.c b/sbin/ifconfig/ifconfig.c
index c9ab382b42f5..35ac555e4f67 100644
--- a/sbin/ifconfig/ifconfig.c
+++ b/sbin/ifconfig/ifconfig.c
@@ -241,6 +241,8 @@ struct	cmd {
 	{ "-link1",	-IFF_LINK1,	setifflags },
 	{ "link2",	IFF_LINK2,	setifflags },
 	{ "-link2",	-IFF_LINK2,	setifflags },
+	{ "monitor",	IFF_MONITOR,	setifflags },
+	{ "-monitor",	-IFF_MONITOR,	setifflags },
 #ifdef USE_IF_MEDIA
 	{ "media",	NEXTARG,	setmedia },
 	{ "mediaopt",	NEXTARG,	setmediaopt },