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Re: [DNSOP] Strange EDNS Header Flags in DNS packet

Nicholas Weaver <nweaver@icsi.berkeley.edu> Tue, 17 December 2013 13:11 UTC

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From: Nicholas Weaver <nweaver@icsi.berkeley.edu>
In-Reply-To: <20131217084735.GA514@nic.fr>
Date: Tue, 17 Dec 2013 05:11:42 -0800
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References: <tencent_02939F0C1F9AD7160D7A8B86@qq.com> <20131217084735.GA514@nic.fr>
To: Stephane Bortzmeyer <bortzmeyer@nic.fr>, Jianjun Ning <to@arey.cn>
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Cc: dnsop <dnsop@ietf.org>, Nicholas Weaver <nweaver@icsi.berkeley.edu>
Subject: Re: [DNSOP] Strange EDNS Header Flags in DNS packet
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On Dec 17, 2013, at 12:47 AM, Stephane Bortzmeyer <bortzmeyer@nic.fr> wrote:

> On Tue, Dec 17, 2013 at 04:21:35PM +0800,
> Jianjun Ning <to@arey.cn> wrote 
> a message of 61 lines which said:
> 
>> ;; OPT PSEUDOSECTION:
>> ; EDNS: version: 0, flags:; MBZ: 0005 , udp: 512
>> ;; QUESTION SECTION:
>> ;www.google.com.hk.             IN      A
>> 
>> The value of field MBZ is 0x0005!!
> 
> The Google authoritative name servers do not seem to return a EDNS
> section in their answers. Therefore, this section has probably been
> added by your resolver, or by a middleman (something which is quite
> common in China).

The great firewall packet injector is easy to detect.  Because it only responds to queries, target your dig (using @) to an IP that isn't hosting a DNS server.

So, eg,

dig +norecurse +bufsize=768 www.google.com.hk @192.150.187.1

(Sends to ICSI, but not our DNS server, so you know the route goes to the west coast of the US)


--
Nicholas Weaver                  it is a tale, told by an idiot,
nweaver@icsi.berkeley.edu                full of sound and fury,
510-666-2903                                 .signifying nothing
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