[Pdns-users] recursor fail to resolve

Sergio P Cesar sergio at winc.net
Fri May 1 16:31:21 UTC 2020

I am new with pdns, just installed a resolver 4.3.0-rc2 to learn and all 
seems to work but stumbled into an issue I cant resolve.

My mailserver failed to deliver email to a few domains, in tracking it I 
found that their DNS will drop the first packet on every new query  but 
will respond on a second query ok and every one after that. (5 minutes 
timeout) it will drop the 1st packet again.
I was expecting the recursor to query the 2nd and 3rd server in their 
list but it does not look like it is doing that.
It seems like it is caching the failure and does not query again at all 
for a while.
I changed packetcache-servfail-ttl=0 and now it looks like after the 3rd 
query attempt it will work as the far end server now respond.
Not sure this is correct setting  or I will have adverse effect setting 
this to 0.

Perhaps I have not set something else that will tell the recursor to try 
the next server if the first one fail to respond or send a second packet 
or a retry.
I used bind to test and it gets a response on the first try. I did not 
try to trace the packets from a bind query.


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