Fall back to TCP on kdc-unresolvable/unreachable errors.  We still have
to wait for UDP to fail, so this might not be ideal.  RT #5868.

Index: src/lib/krb5/os/changepw.c
===================================================================
--- src/lib/krb5/os/changepw.c	(revision 20199)
+++ src/lib/krb5/os/changepw.c	(working copy)
@@ -251,11 +251,22 @@
 				   NULL,
 				   NULL
 		 ))) {
-
-	    /*
-	     * Here we may want to switch to TCP on some errors.
-	     * right?
-	     */
+	    /* if we're not using a stream socket, and it's an error which
+	     * might reasonably be specific to a datagram "connection", try
+	     * again with a stream socket */
+	    if (!useTcp) {
+		switch (code) {
+		case KRB5_KDC_UNREACH:
+		case KRB5_REALM_CANT_RESOLVE:
+		case KRB5KRB_ERR_RESPONSE_TOO_BIG:
+		/* should we do this for more result codes than these? */
+		    krb5int_free_addrlist (&al);
+		    useTcp = 1;
+		    continue;
+		default:
+		    break;
+		}
+	    }
 	    break;
 	}