Iterative_timeout after a certain amount of requests

[ParisConstantinides]

I am trying to run the ZDNS tool on alexa1m using the iterative mode
cat top-1m.csv |./zdns A -iterative -alexa

At the start of the list, I get the expected results:

{"alexa_rank":3567,"data":{"answers":[{"answer":"47.119.172.75","class":"IN","name":"ylsw.com","ttl":600,"type":"A"}],"protocol":"udp","resolver":"106.11.141.114:53"},"name":"ylsw.com","status":"NOERROR","timestamp":"2021-06-17T04:26:32-04:00"}
{"alexa_rank":3349,"data":{"answers":[{"answer":"213.16.167.115","class":"IN","name":"sport-fm.gr","ttl":600,"type":"A"}],"protocol":"udp","resolver":"208.78.70.14:53"},"name":"sport-fm.gr","status":"NOERROR","timestamp":"2021-06-17T04:26:32-04:00"}
{"alexa_rank":4833,"data":{"answers":[{"answer":"52.2.4.21","class":"IN","name":"topcashback.com","ttl":60,"type":"A"},{"answer":"34.202.70.123","class":"IN","name":"topcashback.com","ttl":60,"type":"A"},{"answer":"54.237.74.19","class":"IN","name":"topcashback.com","ttl":60,"type":"A"},{"answer":"23.20.184.113","class":"IN","name":"topcashback.com","ttl":60,"type":"A"}],"protocol":"udp","resolver":"205.251.194.157:53"},"name":"topcashback.com","status":"NOERROR","timestamp":"2021-06-17T04:26:32-04:00"}
{"alexa_rank":4807,"data":{"answers":[{"answer":"23.6.118.43","class":"IN","name":"massimodutti.com","ttl":20,"type":"A"},{"answer":"23.6.118.73","class":"IN","name":"massimodutti.com","ttl":20,"type":"A"}],"protocol":"udp","resolver":"72.246.46.65:53"},"name":"massimodutti.com","status":"NOERROR","timestamp":"2021-06-17T04:26:32-04:00"}
{"alexa_rank":4404,"data":{"answers":[{"answer":"192.230.74.118","class":"IN","name":"tcgplayer.com","ttl":300,"type":"A"},{"answer":"192.230.66.118","class":"IN","name":"tcgplayer.com","ttl":300,"type":"A"}],"protocol":"udp","resolver":"205.251.194.207:53"},"name":"tcgplayer.com","status":"NOERROR","timestamp":"2021-06-17T04:26:32-04:00"}
{"alexa_rank":4566,"data":{"answers":[{"answer":"104.20.135.21","class":"IN","name":"e-hentai.org","ttl":300,"type":"A"},{"answer":"172.67.0.127","class":"IN","name":"e-hentai.org","ttl":300,"type":"A"},{"answer":"104.20.134.21","class":"IN","name":"e-hentai.org","ttl":300,"type":"A"}],"protocol":"udp","resolver":"172.64.32.145:53"},"name":"e-hentai.org","status":"NOERROR","timestamp":"2021-06-17T04:26:32-04:00"}

After a certain amount of time ~15-20sec, I only receive ITERATIVE_TIMEOUT with no results. For almost every other domain after that point, I never get a result.

{"alexa_rank":13888,"data":{"protocol":"","resolver":""},"name":"zp.cc","status":"ITERATIVE_TIMEOUT","timestamp":"2021-06-17T04:27:49-04:00"}
{"alexa_rank":14086,"data":{"protocol":"","resolver":""},"name":"mrw.es","status":"ITERATIVE_TIMEOUT","timestamp":"2021-06-17T04:27:49-04:00"}
{"alexa_rank":14083,"data":{"protocol":"","resolver":""},"name":"micap.es","status":"ITERATIVE_TIMEOUT","timestamp":"2021-06-17T04:27:49-04:00"}
{"alexa_rank":11326,"data":{"protocol":"","resolver":""},"name":"pmkisan.gov.in","status":"ITERATIVE_TIMEOUT","timestamp":"2021-06-17T04:27:49-04:00"}
{"alexa_rank":14410,"data":{"protocol":"","resolver":""},"name":"diggbt.ws","status":"ITERATIVE_TIMEOUT","timestamp":"2021-06-17T04:27:49-04:00"}
{"alexa_rank":14311,"data":{"protocol":"","resolver":""},"name":"mygovid.ie","status":"ITERATIVE_TIMEOUT","timestamp":"2021-06-17T04:27:49-04:00"}
{"alexa_rank":14579,"data":{"protocol":"","resolver":""},"name":"uniqlo.cn","status":"ITERATIVE_TIMEOUT","timestamp":"2021-06-17T04:27:49-04:00"}

I have already tried to change the number of go threads, the iterative-timeout, the timeout, and the cache size, it only changes the initial records that are being resolved and the same issue occurs again but at a later point.

I suspected that I might run out of ports and I have also monitor the number of open ports and it seems that is equal to the number of threads as expected.

Any advice? Am I doing something wrong or is there anything that I am missing?