Explaination of new feature Add tunnel packet support, like ipv4 in ipv4, ipv4 in ipv6, ipv6 in ipv4, ipv6 in ipv6, GRE tunnel

Justification of new feature This could test the performance of tunnel packets.

Can you give some more details here?

It's quite straightforward to set up a tunnel to another host and run iperf3 over the tunnel using appropriate routing / addressing. How does that differ from what you have in mind?

I was thinking something similiar to the --parallel option for client. Iperf3 can simulate upto 128 parallel connection and wanted to see if that can be extended to have 128 different tunnels to the server.

Hrm. As far as I know it's not possible to have multiple GRE or IP-in-IP tunnels between two IP hosts (i.e. a pair of IPv4 addresses). The use of 802.1q VLANs might allow you to do it, by creating tunnels between the VLAN interfaces, but that adds an extra layer of encapsulation and overhead. But in any case the tunneling details are all separate from iperf3.

I admit I'm not 100% sure what you're trying to test, but it feels to me that this could be best done with multiple clients and servers.

Marking this as WontFix, at least for now.