ike-vendor: Add option to send Cisco FLexVPN vendor ID

A new global option enables sending this vendor ID to prevent Cisco
devices from narrowing the initiator's local traffic selector to the
requested virtual IP, so e.g. 0.0.0.0/0 can be used instead.

This has been tested with a "tunnel mode ipsec ipv4" Cisco template but
should also work for GRE encapsulation.

Closes strongswan/strongswan#180.

conf/options/charon.opt

@@ -51,6 +51,18 @@ charon.check_current_path = no
 	connectivity.  It will also trigger a MOBIKE update if NAT mappings were
 	removed during the downtime.
 
+charon.cisco_flexvpn = no
+	Send the Cisco FlexVPN vendor ID payload (IKEv2 only).
+
+	Send the Cisco FlexVPN vendor ID payload, which is required in order to make
+	Cisco brand devices allow negotiating a local traffic selector (from
+	strongSwan's point of view) that is not the assigned virtual IP address if
+	such an address is requested by	strongSwan.  Sending the Cisco FlexVPN
+	vendor ID prevents the peer from narrowing the initiator's local traffic
+	selector and allows it to e.g. negotiate a TS of 0.0.0.0/0 == 0.0.0.0/0
+	instead.  This has been tested with a "tunnel mode ipsec ipv4" Cisco
+	template but should also work for GRE encapsulation.
+
 charon.cisco_unity = no
 	Send Cisco Unity vendor ID payload (IKEv1 only).
 

src/libcharon/sa/ikev2/tasks/ike_vendor.c

@@ -97,7 +97,7 @@ static vid_data_t vids[] = {
 	  "\x88\x2f\xe5\x6d\x6f\xd2\x0d\xbc\x22\x51\x61\x3b\x2e\xbe\x5b\xeb"},
 	{ "Cisco Delete Reason", 0, NULL, 0,
 	  "CISCO-DELETE-REASON" },
-	{ "Cisco FlexVPN Supported", 0, NULL, 0,
+	{ "Cisco FlexVPN Supported", 0, "cisco_flexvpn", 0,
 	  "FLEXVPN-SUPPORTED" },
 	{ "Cisco Copyright (c) 2009", 0, NULL, 0,
 	  "CISCO(COPYRIGHT)&Copyright (c) 2009 Cisco Systems, Inc." },