Use lowest metric interface when multiple interfaces match a route

Currently a route addition using IPAPI or service is skipped if the
route gateway is reachable by multiple interfaces. This changes that
to use the interface with lowest metric. Implemented by

(i)  Do not over-write the return value with TUN_ADAPTER_INDEX_INVALID in
     windows_route_find_if_index() if multiple interfaces match a route.
(ii) Select the interface with lowest metric in adapter_index_of_ip()
     instead of the first one found when multiple interfaces match.

Reported by Jan Just Keijser <janjust@nikhef.nl>

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Tested-by: Jan Just Keijser <janjust@nikhef.nl>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1516815105-17882-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16347.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 3854d4040e0d6fd2a58292e8bb1c1fbae5c17bb1)

diff --git a/src/openvpn/route.c b/src/openvpn/route.c
index 553008bea10622a9b5ad98b73c3fc4c08edae670..d4625794cd14f168785e6258f5dcf737dd766b12 100644 (file)
--- a/src/openvpn/route.c
+++ b/src/openvpn/route.c
@@ -2780,7 +2780,6 @@ windows_route_find_if_index(const struct route_ipv4 *r, const struct tuntap *tt)
         msg(M_WARN, "Warning: route gateway is ambiguous: %s (%d matches)",
             print_in_addr_t(r->gateway, 0, &gc),
             count);
-        ret = TUN_ADAPTER_INDEX_INVALID;
     }
 
     dmsg(D_ROUTE_DEBUG, "DEBUG: route find if: on_tun=%d count=%d index=%d",

diff --git a/src/openvpn/tun.c b/src/openvpn/tun.c
index 90050a8d9163f07e45fc8af138af4218b9e86e0c..ebb15bd3c9c1189917f18e77e88db89fb248b0a8 100644 (file)
--- a/src/openvpn/tun.c
+++ b/src/openvpn/tun.c
@@ -45,6 +45,7 @@
 #include "manage.h"
 #include "route.h"
 #include "win32.h"
+#include "block_dns.h"
 
 #include "memdbg.h"
 
@@ -4480,6 +4481,7 @@ adapter_index_of_ip(const IP_ADAPTER_INFO *list,
     struct gc_arena gc = gc_new();
     DWORD ret = TUN_ADAPTER_INDEX_INVALID;
     in_addr_t highest_netmask = 0;
+    int lowest_metric = INT_MAX;
     bool first = true;
 
     if (count)
@@ -4493,9 +4495,14 @@ adapter_index_of_ip(const IP_ADAPTER_INFO *list,
 
         if (is_ip_in_adapter_subnet(list, ip, &hn))
         {
+            int metric = get_interface_metric(list->Index, AF_INET, NULL);
             if (first || hn > highest_netmask)
             {
                 highest_netmask = hn;
+                if (metric >= 0)
+                {
+                    lowest_metric = metric;
+                }
                 if (count)
                 {
                     *count = 1;
@@ -4509,16 +4516,22 @@ adapter_index_of_ip(const IP_ADAPTER_INFO *list,
                 {
                     ++*count;
                 }
+                if (metric >= 0 && metric < lowest_metric)
+                {
+                    ret = list->Index;
+                    lowest_metric = metric;
+                }
             }
         }
         list = list->Next;
     }
 
-    dmsg(D_ROUTE_DEBUG, "DEBUG: IP Locate: ip=%s nm=%s index=%d count=%d",
+    dmsg(D_ROUTE_DEBUG, "DEBUG: IP Locate: ip=%s nm=%s index=%d count=%d metric=%d",
          print_in_addr_t(ip, 0, &gc),
          print_in_addr_t(highest_netmask, 0, &gc),
          (int)ret,
-         count ? *count : -1);
+         count ? *count : -1,
+         lowest_metric);
 
     if (ret == TUN_ADAPTER_INDEX_INVALID && count)
     {