[Doh] a tad confused on response sizes
bert hubert <bert.hubert@powerdns.com> Tue, 05 June 2018 12:05 UTC
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Date: Tue, 05 Jun 2018 14:05:10 +0200
From: bert hubert <bert.hubert@powerdns.com>
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Subject: [Doh] a tad confused on response sizes
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Dear DOH-people, As I'm implementing DOH in dnsdist (expect something you can try later this week), I am a bit confused. The question is what maximum response size I should send in the absence of an EDNS buffer size. So let's say a query comes in without EDNS for www.whitehouse.gov, but the answer exceeds 512 bytes. Should I truncate? I have read the draft and previous discussion, which has led to: Also note that while [RFC1035] says "Messages carried by UDP are restricted to 512 bytes", that was later updated by [RFC6891]. This protocol allows DNS on-the-wire format payloads of any size." This is not explicit on what an implementation should do, only what the protocol could support. Some further text: A DNS API server is allowed to answer queries with any valid DNS response. For example, a valid DNS response might have the TC (truncation) bit set in the DNS header to indicate that the server was not able to retrieve a full answer for the query but is providing the best answer it could get. A DNS API server can reply to queries with an HTTP error for queries that it cannot fulfill. In this same example, a DNS API server could use an HTTP error instead of a non- error response that has the TC bit set. This seems says sending a TC response is some kind of error, which implies a DNS API server should be willing to send 65 kilobyte answers. I think for the new usecases, this would be a fine default. However, there might be UDP-to-DOH bridges which would then need to put explicit EDNS buffersize of 512 in there if they get non-EDNS adorned UDP queries. If the '65 kilobyte' interpretation is correct, I can supply text that will hopefully make this explicit and unconfuse future implementers. Bert
- Re: [Doh] [Ext] a tad confused on response sizes Star Brilliant
- Re: [Doh] [Ext] a tad confused on response sizes Andrew Sullivan
- Re: [Doh] [Ext] a tad confused on response sizes Patrick McManus
- Re: [Doh] [Ext] a tad confused on response sizes Massimiliano Fantuzzi
- Re: [Doh] [Ext] a tad confused on response sizes Ray Bellis
- [Doh] a tad confused on response sizes bert hubert
- Re: [Doh] a tad confused on response sizes Dave Lawrence
- Re: [Doh] [Ext] a tad confused on response sizes Paul Hoffman
- Re: [Doh] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Paul Hoffman
- Re: [Doh] [Ext] a tad confused on response sizes Andrew Sullivan
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Stephane Bortzmeyer
- Re: [Doh] [Ext] a tad confused on response sizes Stephane Bortzmeyer
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Andrew Sullivan
- Re: [Doh] [Ext] a tad confused on response sizes Star Brilliant
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Paul Hoffman
- Re: [Doh] [Ext] a tad confused on response sizes Dave Lawrence
- Re: [Doh] [Ext] a tad confused on response sizes Dave Lawrence
- Re: [Doh] [Ext] a tad confused on response sizes Star Brilliant
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Star Brilliant
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch
- Re: [Doh] [Ext] a tad confused on response sizes Paul Hoffman
- Re: [Doh] [Ext] a tad confused on response sizes Andrew Sullivan
- Re: [Doh] [Ext] a tad confused on response sizes Tony Finch