> I have reviewed this document as part of the security directorate's > ongoing effort to review all IETF documents being processed by the > IESG. These comments were written primarily for the benefit of the > security area directors. Document editors and WG chairs should treat > these comments just like any other last call comments. > > DNS is not my area of expertise but the document clearly explains > the nature of the problem to be solved (DOS attacks that employ > DNS servers as amplifiers) and the recommendations for solving the > problem (employing ingress filtering to prevent IP address spoofing > and changing nameservers to provide recursive name lookup service > only to the intended clients). > > I have no issue with the main content of the document. It does seem > like a worthwhile recommendation. However, I have a few comments. > > The Introduction seems a bit defensive in stating that the DOS attacks > are not due to any flaw in the design of DNS or its implementations. > While the blame for the attacks lies with the attackers, some aspects > of nameserver configuration, behavior, and even protocol design make > the systems vulnerable to these attacks. I suggest that the defensive > language be removed. No, the blame lies with the parties not implementing BCP 38. A rogue end site should not be able to inject spoofed packets. > Although I agree that ingress filtering is a good solution to this > problem and provides many other benefits since it addresses many > different attacks that involve spoofed IP addresses, the document > states repeatedly that ingress filtering is the only solution to > the problem. Ingress filtering may be the best solution but it is > NOT the only solution, as evidenced by the other measures described > in the document. The other measure reduce the number of amplifiers. There are however enough other amplifiers out there that many argued that this whole docuement was a waste of time as it can't reduce the problem enough. That being said they wern't going to try to stop it being published. At best this document helps build a "Clue x 4" bat. > None of these measures (including increased use > of ingress filtering) will provide complete and absolute protection > against DOS attacks that use nameservers as attack amplifiers. It reduces the places to launch these attacks to ISP's routers if BCP 38 is correctly deployed by ISP's. All the end sites should be filtered as well as any internal subnets of the ISP itself. If you have a rogue ISP then they should be disconnected by their peers / transits. > Employing all of the measures as appropriate while emphasizing > the huge benefits of ingress filtering seems like the best approach. > So I suggest that the wording in the document be toned down to take > a more balanced approach to the problem. > > Finally, I wonder whether other more fundamental techniques for > addressing the problem have been explored. For instance, if DNS clients > were required to perform a simple handshake before a DNS server sent > a long response, fake requests would provide little amplification. > For example, requests that elicit long responses could prompt a > shift to TCP. The DNS already does this. The DNS is optimised so that the normal responses go via UDP and the exceptional responses via TCP. > Of course, this would have other unpleasant side effects > such as slowing down the processing of DNS requests with long responses > and troubles getting DNS requests through firewalls. I'm not suggesting > that this approach be discussed in this document, simply that it be > considered (which probably has already been done). It's been consided, tried, and proved a dismal failure. > Thanks, > > Steve > > _______________________________________________ > Ietf mailing list > Ietf@xxxxxxxx > https://www1.ietf.org/mailman/listinfo/ietf -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews@xxxxxxx _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf