% ip verify unicast reverse-path % % and according to Paul Ferguson (co-author of RFC 2267) it's in use by % many ISPs. Apparently this is very-low overhead. Paul has also indicated % the use of extended access lists on Cisco routers is very low overhead, % especially on routers using distributed express forwarding. while i hate to question mr. ferguson, it's my understanding that many isps have found this feature to be unusable due to network design. ----------------------------------------------------------------------------- bryan s. blank bryan@supernet.net (443)394-9529 tele (410)995-2191 page (410)802-6998 emer