North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

RE: large organization nameservers sending icmp packets to dns servers.

  • From: william(at)elan.net
  • Date: Wed Aug 08 19:13:24 2007



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
[email protected]