[Dnsmasq-discuss] Does dnsmasq support forwarding EDNS queries?

Simon Kelley simon at thekelleys.org.uk
Sat May 14 21:31:43 BST 2016


On 10/05/16 22:03, Jake Gold wrote:
> Hello,
> 
> I'm using dnsmasq as a local caching resolver and some of my queries result
> in large answers (~1300 bytes) that are truncated without EDNS.
> 
> When I query my local dnsmasq daemon:
> 
> dig @localhost <record.with.big.answer>
> 
> dig sends a query to dnsmasq using EDNS but dnsmasq forwards that query to
> its upstream server without using EDNS.
> 
> Is this just how dnsmasq works or is there a way to make dnsmasq forward
> EDNS queries? (Or am I missing something?)
> 
> Thanks in advance.
> 

EDNS (in this context) is a way for the two ends of a DNS transaction to
negotiate the maximum size of reply that can be sent over UDP. Dnsmasq
will not strip an EDNS header from a query it forwards, but it might
reduce the "maximum UDP size" field, based on the config setting
--edns-packet-max.


In the end, if an answer is too big, the query has to be re-done over
TCP. A common problem with this is firewalls which block port 53 for TCP.


Cheers,

Simon.





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