2 votes

How to trace NAT traffic (port-forwarding) from guest VM back to host

I assume that is opened by VirtualBox process (you may verify that with lsof -i TCP -Pn | grep LISTEN). To strictly answer your question - you may take a list of ports opened by ...
2 votes

Can a DNS server accept queries from both IPv4 and IPv6 clients?

You have to configure your server accordingly, but this is really a basic feature existing since a long time. https://ftp.isc.org/isc/bind9/cur/9.19/doc/arm/html/reference.html#namedconf-statement-...
1 vote

How to get the kernel not to treat a packet injected through tun/tap as a 'martian'

This behaviour is due to reverse path filtering, an attempt to avoid handling packets which come in on the 'wrong' interface. This can be turned off with for device in /proc/sys/net/ipv4/conf/* do ...
1 vote

iptables/nat/prerouting ignores UDP packets?

Same thing here. As the last thing to check, check the conntrack table. In my case, resetting the tracked connections make the rules work instantly. apt install conntrack -y # see current UDP ...
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