socat gives error (read(6, 0xf97acc0, 8192): Permission denied)

I'm trying to use socat as a port mapper to map IPv4 connections to my OpenVPN server running behind a DS-Lite IPv6 cable connection. //edit I tried with a non root user and root. But I get the same result with both users. //edit Goal is to be able to connect from my mobile phone via OpenVPN to my (IPv4) smart home devices. From the server running socat I can ping6 my router at home. IPv6 port forwarding is enabled as well and forwards 1194/udp to the raspberry running the OpenVPN server at home. Problem is now that I'm seeing an error from socat as I try to connect OpenVPN from my mobile. root@scw-31f6c8:~/bin# socat -d -d UDP4-LISTEN:63530,fork UDP6:xxx.dynv6.net:1194 2017/12/27 13:53:01 socat N listening on UDP AF=2 0.0.0.0:63530 2017/12/27 13:53:07 socat N accepting UDP connection from AF=2 xx.xxx.xxx.xx:1319 2017/12/27 13:53:07 socat N forked off child process 15429 2017/12/27 13:53:07 socat N listening on UDP AF=2 0.0.0.0:63530 2017/12/27 13:53:07 socat N opening connection to AF=10 [2a02:810c:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx]:1194 2017/12/27 13:53:07 socat N successfully connected from local address AF=10 [2001:0bc8:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx]:41641 2017/12/27 13:53:07 socat N starting data transfer loop with FDs [5,5] and [6,6] 2017/12/27 13:53:07 socat E read(6, 0xf97acc0, 8192): Permission denied 2017/12/27 13:53:07 socat N exit(1) 2017/12/27 13:53:07 socat N childdied(): handling signal 17 2017/12/27 13:53:07 socat W waitpid(): child 15429 exited with status 1 On first sight everything looks good until it hits read(6, 0xf97acc0, 8192): Permission denied. Currently I cannot identify if this is a socat error on the server running it, or if it is related to a communication issue from socat to my IPv6 endpoint at home. Any pointer on how to find out what's wrong? **//edit** I tried it as well on different machines (uberspace, scaleway) To be sure it is not related to a bad server side configuration. Might be an indicator that something is wrong on my end. But currently I don't see it.