diff --git a/src/capwap/sock.h b/src/capwap/sock.h
index e644e403..8417115e 100644
--- a/src/capwap/sock.h
+++ b/src/capwap/sock.h
@@ -53,6 +53,9 @@ extern int sock_getbroadcastaddr(const struct sockaddr * addr,struct sockaddr *
 extern void sock_addrinit(struct sockaddr *addr,int type);
 extern int sock_set_dontfrag(int sock,int val);
 
+
+extern char * sock_get_primary_if(int family);
+
 /*
 enum {
 	SOCK_IFADDR_ADDRESS,