yum in CentOS 6.9 VM insists on using ipv6 mirrors after mangling with iptables in host machine

I am learning to handle iptables when but I had to port forward over a NAT host machine to a server on a VM running CentOS 6.9. Host machine is running Kubuntu 18.04.

After trying some iptable rules and ufw (which I promptly disabled after), yum on the VM insists on picking ipv6 mirrors. I have tried new VMs but it still doesn't work.

I installed iptables-persistent on host and despite running sudo iptables -F it seems that the rules are not flushed from /etc/iptable/rules.v4 Now I am worried if deleting the entire file would result in instability with my host machine and doesn't solve it at all.