Re: [Doh] [Ext] a tad confused on response sizes

Tony Finch <dot@dotat.at> Tue, 05 June 2018 22:26 UTC

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From: Tony Finch <dot@dotat.at>
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Date: Tue, 5 Jun 2018 23:26:22 +0100
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References: <20180605120510.GA29047@server.ds9a.nl> <CFEAAD6E-4F9D-4DB5-A362-21775D74F84A@icann.org> <alpine.DEB.2.11.1806051515510.1809@grey.csi.cam.ac.uk> <663E7B21-9107-4A2B-9DEB-E13475A4E5FF@icann.org> <alpine.DEB.2.11.1806051604150.1809@grey.csi.cam.ac.uk> <20180605152355.6tlbeqvt7luklwjl@nic.fr> <alpine.DEB.2.11.1806051710290.1809@grey.csi.cam.ac.uk> <BYAPR19MB22489BE90FE768BCB13BD40B94660@BYAPR19MB2248.namprd19.prod.outlook.com> <alpine.DEB.2.11.1806051759430.1809@grey.csi.cam.ac.uk> <BYAPR19MB2248B0ADD763FF82E8C6C2E194660@BYAPR19MB2248.namprd19.prod.outlook.com> <alpine.DEB.2.11.1806051908040.1809@grey.csi.cam.ac.uk> <BYAPR19MB22489076D7E7A6780F78CCF094660@BYAPR19MB2248.namprd19.prod.outlook.com> <alpine.DEB.2.11.1806052125170.1809@grey.csi.cam.ac.uk> <8CB4E291-95D8-4AC2-9CBA-84D54A6E93DA@icann.org>
To: Paul Hoffman <paul.hoffman@icann.org>
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Subject: Re: [Doh] [Ext] a tad confused on response sizes
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> On 5 Jun 2018, at 23:10, Paul Hoffman <paul.hoffman@icann.org>; wrote:
> 
> Resolver 1 sends a query to a Resolver 2 (who allows forwarding) over TCP. Resolver 2 asks an authoritative,  gets a response with TC bit set on, tries on TCP, and gets a failure on TCP. Resolver 2 should send the partial answer it got over UDP to Resolver 1. That answer to Resolver 1 should have the TC bit set on, or not, depending on what you think that RFC 1035 "implies".

In my experience this results in a SERVFAIL.  RFC 2181 has a specific instruction not to do what you suggest:

>> When a DNS client receives a reply with TC set, it should ignore that response, and query again, using a mechanism, such as a TCP connection, that will permit larger replies. <<

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>;  http://dotat.at