Lately I bought a couple HDDs to finish my home made NAS running OpenMediaVault Debian. I personally think that IPv6 should be supported by any means, so I activated it right after finishing the installation process and everything was working fine. I shut down the system during the night hours because there was no reason to leave it on because I had not yet copied any data onto the NAS.
Next day the system got stuck at bootup! At first I thought something messed up the resolv.conf because the bootup process was throwing a couple errors that indicated something like that but in the end it was the NIC waiting for an IPv6 lease from the DHCP server runnig on my fritzbox (don’t judge me, if I could this thing would take a visit to the trash can asap). The DHCP was somehow misconfigured so that Debian was waiting endlessly for an address.
I fixed it by enabling IA_PD and IA_NA in the fritzbox GUI and voilà Debian finished booting right away.