On Tue, 7 Aug 2007, Donald Stahl wrote:
All things being equal (which they're usually not) you could use the ACK response time of the TCP handshake if they've got TCP DNS resolution available. Though again most don't for security reasons... Then most are incredibly stupid.
Several anti DoS utilities force unknown hosts to initiate a query via TCP in order to be whitelisted. If the host can't perform a TCP query then they get blacklisted.
How is that an "anti DoS" technique when you actually need to return an answer via UDP in order to force next request via TCP? Or is this techinque based on premise that an attacker will not spoof packets and thus will send flood of DNS requests to server from same IP (set of ips)? If so the result would be that attacker could in fact use TCP just as well as UDP. -- William Leibzon Elan Networks william@elan.net