Networking benchmark use internal IP to ping, so VMs on different subnets are not reachable

I used a combination of one personal static server and one google cloud VM to try run ping benchmark. I found that the benchmark was using internal IPs in its run phase, so both the machines were unable to ping each other, since they were on different networks. To try solve the issue, I provided the external IP of the static_vm in place of the internal IP, and now the google VM was able to ping my server, but not vice versa. I also tried providing "--ip_addresses=EXTERNAL" in the command line used to execute the benchmark, to no results. Kindly provide some insights on how to solve this issue!

Warning message: is not reachable from
Here is the static_vm_file that I used:

```
[
{
"ip_address": "",
"user_name": "root",
"keyfile_path": "/root/.ssh/id_rsa",
"internal_ip": ""
}
]
```

And this is the command line option that I used:
`./pkb.py --benchmarks=ping --static_vm_file=india.json --ip_addresses=EXTERNAL`