protected void disconnectInterface( String hostId, String ifId ) {
		Host h = hosts.get( hostId );
		if( h == null ) return;
		String linkId = h.interfaceLinkIds.get(ifId);
		if( linkId == null ) return;
		Link l = links.get(linkId);
		if( l != null ) {
			if( hostId.equals(l.host1) && ifId.equals(l.if1) ) {
				l.host1 = null;
				l.if1   = null;
			}
			if( hostId.equals(l.host2) && ifId.equals(l.if2) ) {
				l.host2 = null;
				l.if2   = null;
			}
		}
		h.interfaceLinkIds.remove(ifId);
	}