On Tue, Dec 23, 1997 at 05:32:15PM -0600, Phil Howard wrote:
When a packet arrives, take note of the interface and gateway it came from. Check the route tables for where a reply to this packet could be delivered. Don't choose only the best route, but compare where the packet came from with all valid reply routes (except broad defaults larger than a certain size that can be configured). If the packet came from where it is valid to reply, then allow the packet to proceed. If not, then discard it (an ICMP probably won't make it back to the right place anyway).
Oh ghod... weren't you around, Phil, when _I_ got roundly trounced and reviled as a clueless newbie about 3 months ago for alomst exactly the same solution? The outcome as I recall, was that the only practical thing to do was ingress filtering at boundary routers, if they would. Cheers, -- jra -- Jay R. Ashworth jra@baylink.com Member of the Technical Staff Unsolicited Commercial Emailers Sued The Suncoast Freenet "Two words: Darth Doogie." -- Jason Colby, Tampa Bay, Florida on alt.fan.heinlein +1 813 790 7592