public void validateModel() {
    for (TVC c : connectionsSortedUp) {
      if (!c.validate()) {
        throw new RuntimeException("Validation failed: connection is managed by wrong firewall, c=" + c);
      }

      int managedFw = c.getManagerFirewallId();
      for (Firewall fw : firewalls) {
        if (fw.getId() != managedFw && fw.isManagesConnection(c)) {
          throw new RuntimeException("Validation failed: Two firewalls manage one connection: " + managedFw + ", " + fw.getId());
        }
      }
    }
  }