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>

diff --git a/src/openvpn/route.c b/src/openvpn/route.c
index 3e2d0bde4a0194525973aa52b4cdc3b877275606..ca8b182bd0baa8f5bd31ae5473098d9add398212 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 926052e2f4338795c1fd893b2268af0267de6144..253d884b9fc9ef475f21175073cb54722c09ecf0 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)
     {