[dnsdist] Filter SERVFAILS by destination domain

[Alejandro Adroher Mellado]

Hi all, 

I'm working with dynamic blocks  on my environment. 
I'm doing the next, easy currently:

function maintenance()
    toBlock = exceedQRate(300, 10)
    for k, v in pairs(toBlock) do
        if (whitelisted:match(k))
        then
            toBlock[k] = nil
        end
    end
    addDynBlocks(toBlock, "Exceeded query rate", 60)
end

-----------------------------------------------------------------------

Now I would like to go for the SERVFAILS, I must have my resolver opened by company reasons so, I would like to deal with that.

I know I can use --> exceedServFails(rate, seconds)

But I would do that by source IP and also by requested serverfailed domain, I mean, respecting my whitelist I would like to drop an IP when it gets more than X SERVFAILS for one specific domain. 

Today I received responded like 500k SERVERFAILS asking for xxxxxxxx.shop.vvtjhq.com, I added a rule to manually block the domain but I would like to improve my script.

I know how to rate by IP but no for the domain queried. I´m on production and I don't want to broke anything doing wrong tests .. XD

Can someone show me one way?

Thank a lot.

Ale