[PATCH] vxlan: force user to set port value

[Stephen Hemminger <stephen@networkplumber.org>]

This change shifts burden onto the users to choose the UDP port value.
There is no default value, the destination port must be specified.

This is a migration compromise. The initial development of VXLAN
used UDP port 5287 but now there is an official assigned port for
VXLAN.  The kernel can't change because of legacy compatibility
but new deployments should not use the legacy port value.

---
 ip/iplink_vxlan.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/ip/iplink_vxlan.c b/ip/iplink_vxlan.c
index 2d93ee2..263feca 100644
--- a/ip/iplink_vxlan.c
+++ b/ip/iplink_vxlan.c
@@ -53,7 +53,8 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 	__u8 noage = 0;
 	__u32 age = 0;
 	__u32 maxaddr = 0;
-	__u16 dstport = 4789;
+	__u16 dstport = 0;
+	int dst_port_set = 0;
 	struct ifla_vxlan_port_range range = { 0, 0 };
 
 	while (argc > 0) {
@@ -131,6 +132,7 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 			NEXT_ARG();
 			if (get_u16(&dstport, *argv, 0))
 				invarg("dst port", *argv);
+			dst_port_set = 1;
 		} else if (!matches(*argv, "nolearning")) {
 			learning = 0;
 		} else if (!matches(*argv, "learning")) {
@@ -161,10 +163,18 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 		}
 		argc--, argv++;
 	}
+
 	if (!vni_set) {
 		fprintf(stderr, "vxlan: missing virtual network identifier\n");
 		return -1;
 	}
+
+	if (!dst_port_set) {
+		fprintf(stderr, "vxlan: destination port not specified\n"
+			"Use 'dstport 4789' to get the IANA assigned value\n");
+		return -1;
+	}
+
 	addattr32(n, 1024, IFLA_VXLAN_ID, vni);
 	if (gaddr)
 		addattr_l(n, 1024, IFLA_VXLAN_GROUP, &gaddr, 4);
@@ -179,6 +189,7 @@ static int vxlan_parse_opt(struct link_util *lu, int argc, char **argv,
 	addattr8(n, 1024, IFLA_VXLAN_RSC, rsc);
 	addattr8(n, 1024, IFLA_VXLAN_L2MISS, l2miss);
 	addattr8(n, 1024, IFLA_VXLAN_L3MISS, l3miss);
+
 	if (noage)
 		addattr32(n, 1024, IFLA_VXLAN_AGEING, 0);
 	else if (age)
-- 
1.7.10.4