I was talking about a different filter. The one I listed was designed to prohibit someone at an exchange point from using our network for transit. I agree, you'd want to do what you describe to prevent IP spoofing. Avi
"Avi" == Avi Freedman <freedman@netaxs.com> writes:
Avi> This is actually an incoming filter... Avi> acc 102 permit ip any 198.138.103.0 0.0.0.255
Ummmm.... disclaimer, I'm not an expert on this, but according to my understanding of how Cisco access lists work, the incoming filter you showed actually does nothing at all. The normal situation is that packets are coming in from random addresses, destined for your internal network. There is nothing in this filter that prevents your own source addresses from being spoofed outside your border.
It seems to me that you want something more like this, which is what we have in place:
acc 102 deny ip 198.138.103.0 0.0.0.255 any ... acc 102 permit any any
It seems to work for us. Please let me know if I'm missing something here!
-- Bruce Robertson, President/CEO Great Basin Internet Services, Inc. +1-702-348-7299 fax: +1-702-348-9412