I'm going to run a grpc server on IPv4 address like this:

server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))
protoc_pb2_grpc.add_ProtocServicer_to_server(StockProtocServicer(), server)
server.add_insecure_port('0.0.0.0:5000')
server.start()

But it it's listening to IPv6. Here is the output for lsof -i -n -P | grep 5000:

python    7302             dev    6u  IPv6 224100      0t0  TCP *:5000 (LISTEN)

I've tested listening on IPv6 to see what happens, like this:

server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))
protoc_pb2_grpc.add_ProtocServicer_to_server(UserProtocServicer(), server)
server.add_insecure_port('[::]:5000')
server.start()

but the result was the same:

python    7366             dev    6u  IPv6 225782      0t0  TCP *:5000 (LISTEN)

I also tried to use the actual IP address instead of 0.0.0.0:

python    7392             dev    6u  IPv6 226111      0t0  TCP 192.168.1.23:5000 (LISTEN)

Although I can use the server's IPv4 address on my client, I want to run the server only on IPv4. How can I do that?

TLDR: If you use an IPv4 address, it's using IPv4, not IPv6. You have what you want, even though lsof says IPv6.

lsof and "IPv4-mapped IPv6 address" explanation

When using the IPv4 address, my python client still shows type as IPv6 when lsof -nP -i4TCP | grep appname.

From man lsof:

When an open IPv4 network file's address is mapped in an IPv6 address, the open file's type will be IPv6, not IPv4, and its display will be selected by '6', not '4'.

This means our applications uses the IPv6 network file/socket, but it uses the IPv4 protocol. Apparently, this is convenient for applications (e.g. python, gRPC) to handle - they don't have to worry about IPv4 and IPv6, they just support IPv6 and it will map to IPv4 if needed.

For more information about mapped addresses, see

• Purpose of IPv4 mapped IPv6 address.
• IPv4-mapped IPv6 addresses

Bonus question:

What if you only have the domain name (e.g. google.com) and want to use IPv4, not IPv6, even though the IPv6 DNS record (AAAA) exists: dig AAAA google.com).

Answer: To do this, you could use dig A example.com and use that the server address. I am looking for a better way to do this though.