Regarding EDNS Responses.

Mark Andrews marka at isc.org
Wed Oct 28 05:52:03 UTC 2009


In message <001501ca5785$257c7220$2101120a at china.huawei.com>, Ashwin writes:
> 
> Hi All,
> 
>  RFC 2671 mentions in Section 5.3
> 
> Responders who do not understand these protocol extensions are
> expected to send a response with RCODE NOTIMPL, FORMERR, or
> SERVFAIL.
> 
> However the above mentioned error codes are shared [SERVFAIL, NOTIMPL] are
> shared, so how do we ascertain that the error code returned is an indication
> that a particular server is non-EDNS, since the error might be returned due
> to some other reason also.
> 
> So essentially my query is how do we decide that a particular server is EDNS
> or not? Can it be assumed that each time the above three error codes are
> returned , it signifies that the DNS server is not EDNS capable?

You assume it is EDNS if it is in response to a EDNS query and retry
w/o EDNS.  It the problem is EDNS the plain DNS query will succeed.
If it is not EDNS the plain EDNS query will fail.

  
> Regards
> 
> Ashwin

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org



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