nanog mailing list archives
Re: DNS question, null MX records
From: Douglas Otis <dotis () mail-abuse org>
Date: Wed, 16 Dec 2009 16:41:46 -0800
On 12/16/09 4:08 PM, Joe Abley wrote:
On 2009-12-17, at 00:02, Douglas Otis wrote:To avoid server access and hitting roots: host-1.example.com. IN A 192.0.2.0
>> ... >> host-10.example.com. IN A 192.0.2.9
example.com. IN MX 0 host-1.example.com.
>> ... >> example.com. IN MX 90 host-10.example.com.
This will still cause DNS requests to be sent towards 192.0.2.0 and 192.0.2.9, and they may not be dropped at the first router depending on local conditions. There are implications of state in the local resolver. Choosing MX RDATA with a name that is known not to exist ideally will only exercise the local cache for the non-existent name, since it will perhaps not be the first such query and the non-existence will already be cached. SINK.ARPA doesn't exist today. The document I referred to only exists to enforce that non-existence in the future; operationally you could install MX records towards SINK.ARPA today and get the desired effect, regardless of the state of the document.
The ARPA technique, as does pointing to the root, relies upon negative caching of non-existent A records. This allows spammers to quickly determine the inability to resolve addresses for MX hostnames and thereby bypass connection attempts. Offering a sequence in the TEST-NET block was to thwart the alternative of directly using the A record, which is likely to point to a server. If MX TEST-NET became common, legitimate email handlers unable to validate messages prior to acceptance might find their server resource constrained when bouncing a large amount of spam as well. -Doug
Current thread:
- Re: DNS question, null MX records, (continued)
- Re: DNS question, null MX records Patrick W. Gilmore (Dec 15)
- Re: DNS question, null MX records Dave Sparro (Dec 15)
- Re: DNS question, null MX records Joe Abley (Dec 16)
- RE: DNS question, null MX records Eric J Esslinger (Dec 15)
- Re: DNS question, null MX records Andy Davidson (Dec 15)
- Re: DNS question, null MX records Douglas Otis (Dec 15)
- Re: DNS question, null MX records Mark Andrews (Dec 15)
- Re: DNS question, null MX records Tony Finch (Dec 16)
- Re: DNS question, null MX records Douglas Otis (Dec 16)
- Re: DNS question, null MX records Joe Abley (Dec 16)
- Re: DNS question, null MX records Douglas Otis (Dec 16)
- Re: DNS question, null MX records Paul Vixie (Dec 16)
- Re: DNS question, null MX records Douglas Otis (Dec 16)
- Re: DNS question, null MX records Paul Vixie (Dec 16)
- RE: DNS question, null MX records Jay Mitchell (Dec 18)
- Re: DNS question, null MX records Douglas Otis (Dec 15)
- Re: DNS question, null MX records Tony Finch (Dec 17)
- Re: DNS question, null MX records Douglas Otis (Dec 17)
- Re: DNS question, null MX records James Hess (Dec 17)
- Re: DNS question, null MX records Mark Andrews (Dec 17)
- Re: DNS question, null MX records Tony Finch (Dec 18)