text: Title: Reachability Issue for private swarm
  Body: I am creating a private swarm using backbone peer hosted at aws EC2 instance and trying to connect my machine's GPU but getting reachability issues.
  I have followed the list of commands listed below.
  ```python3 -m petals.cli.run_dht --host_maddrs /ip4/0.0.0.0/tcp/31337 --identity_path bootstrap1.id```
  
  I am getting reachability as False on backbone peer:
  ```reachability.rpc_check(remote_peer=...YELDdS, check_peer=...YELDdS) -> False```
  
  I have followed commands from petals documentation for creating backbone peer and running petals server
  ```python3 -m petals.cli.run_server meta-llama/Llama-2-13b-hf  --token mytoken   --initial_peers /ip4/EC2_public_ip/tcp/31337/p2p/Qm_mybackbone_peer```
  
  