diff --git a/nest/iface.c b/nest/iface.c
index f6f33a99..5f356fd8 100644
--- a/nest/iface.c
+++ b/nest/iface.c
@@ -15,6 +15,8 @@
 
 static pool *if_pool;
 
+u32 router_id;
+
 /*
  *	Neighbor Cache
  *
@@ -196,7 +198,7 @@ if_dump_all(void)
   debug("Known network interfaces:\n");
   WALK_LIST(i, iface_list)
     if_dump(i);
-  debug("\n");
+  debug("\nRouter ID: %08x\n\n", router_id);
 }
 
 static inline int
@@ -324,6 +326,25 @@ if_feed_baby(struct proto *p)
     p->if_notify(p, IF_CHANGE_CREATE | ((i->flags & IF_UP) ? IF_CHANGE_UP : 0), NULL, i);
 }
 
+void
+auto_router_id(void)			/* FIXME: What if we run IPv6??? */
+{
+  struct iface *i, *j;
+
+  if (router_id)
+    return;
+  j = NULL;
+  WALK_LIST(i, iface_list)
+    if ((i->flags & IF_UP) &&
+	!(i->flags & (IF_UNNUMBERED | IF_LOOPBACK | IF_IGNORE)) &&
+	(!j || ipa_to_u32(i->ip) < ipa_to_u32(j->ip)))
+      j = i;
+  if (!j)				/* FIXME: allow configuration or running without RID */
+    die("Cannot determine router ID, please configure manually");
+  router_id = ipa_to_u32(j->ip);
+  debug("Router ID set to %08x (%s)\n", router_id, j->name);
+}
+
 void
 if_init(void)
 {
diff --git a/nest/iface.h b/nest/iface.h
index ff6ddeea..ea937207 100644
--- a/nest/iface.h
+++ b/nest/iface.h
@@ -54,6 +54,7 @@ void if_dump_all(void);
 void if_update(struct iface *);
 void if_end_update(void);
 void if_feed_baby(struct proto *);
+void auto_router_id(void);
 
 /*
  *	Neighbor Cache. We hold (direct neighbor, protocol) pairs we've seen
diff --git a/sysdep/unix/main.c b/sysdep/unix/main.c
index 4c60ee62..3d927cb7 100644
--- a/sysdep/unix/main.c
+++ b/sysdep/unix/main.c
@@ -86,6 +86,7 @@ main(void)
   signal_init();
 
   scan_if_init();
+  auto_router_id();
 
   protos_start();