[dnsdist] Sending additional info from dnsdist to recursor

Remi Gacogne remi.gacogne at powerdns.com
Thu Aug 29 14:38:24 UTC 2019

Hi Brian,

On 8/19/19 3:46 PM, Brian Sullivan wrote:
> I have read through the documentation and maybe I missed this. Is there
> a way to signal additional information from dnsdist to pdns recursor?
> For example, I'd like when a rate limiter triggers to tag the query
> somehow so that in the recursor I could do some special processing. Open
> to any suggestions that people have used ... 

The issue there is that the DNS protocol does not really provide any
easy way to add information into an existing DNS packet, unlike HTTP and
its headers.
Some users have managed to get something working by adding trailing data
to the packet (see [1]), which I don't really recommend.
Other options would involve writing something into a shared database of
some kind in dnsdist and reading it back in the recursor, but that's a
bit convoluted.

[1]: https://dnsdist.org/reference/dq.html#DNSQuestion:setTrailingData

Best regards,
Remi Gacogne
PowerDNS.COM BV - https://www.powerdns.com/

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