socket.error:[errno 99] cannot assign requested address and namespace in python

Question

My server software says errno99: cannot assign requested address while using an ip address other than 127.0.0.1 for binding.

But if the IP address is 127.0.0.1 it works. Is it related to namespaces?

I am executing my server and client codes in another python program by calling execfile(). I am actually editing the mininet source code.I edited net.py and inside that I used execfile('server.py') execfile('client1.py') and execfile('client2.py').So as soon as "sudo mn --topo single,3" is called along with the creation of 3 hosts my server and client codes will get executed.I have given my server and client codes below.

#server code
import select 
import socket 
import sys 
backlog = 5 
size = 1024 
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 
server.bind(("10.0.0.1",9999)) 
server.listen(backlog) 
input = [server] 
running = 1 
while running: 
    inputready,outputready,exceptready = select.select(input,[],[]) 
    for s in inputready: 
        if s == server: 
            client, address = server.accept() 
            input.append(client)
        else: 
            l = s.recv(1024)
            sys.stdout.write(l)
server.close()

#client code
import socket
import select
import sys
import time
while(1) :
    s,addr=server1.accept()    
    data=int(s.recv(4))
    s = socket.socket()
    s.connect(("10.0.0.1",9999))
    while (1):
        f=open ("hello1.txt", "rb")
        l = f.read(1024)
        s.send(l)
        l = f.read(1024)
        time.sleep(5)
s.close()

Answer 1

This error will also appear if you try to connect to an exposed port from within a Docker container, when nothing is actively serving the port.

On a host where nothing is listening/bound to that port you'd get a No connection could be made because the target machine actively refused it error instead when making a request to a local URL that is not served, eg: localhost:5000. However, if you start a container that binds to the port, but there is no server running inside of it actually serving the port, any requests to that port on localhost will result in:

• [Errno 99] Cannot assign requested address (if called from within the container), or
• [Errno 0] Error (if called from outside of the container).

---

You can reproduce this error and the behaviour described above as follows:

Start a dummy container (note: this will pull the python image if not found locally):

docker run --name serv1 -p 5000:5000 -dit python

Then for [Errno 0] Error enter a Python console on host, while for [Errno 99] Cannot assign requested address access a Python console on the container by calling:

docker exec -it -u 0 serv1 python

And then in either case call:

import urllib.request
urllib.request.urlopen('https://localhost:5000')

I concluded with treating either of these errors as equivalent to No connection could be made because the target machine actively refused it rather than trying to fix their cause - although please advise if that's a bad idea.

---

I've spent over a day figuring this one out, given that all resources and answers I could find on the [Errno 99] Cannot assign requested address point in the direction of binding to an occupied port, connecting to an invalid IP, sysctl conflicts, docker network issues, TIME_WAIT being incorrect, and many more things. Therefore I wanted to leave this answer here, despite not being a direct answer to the question at hand, given that it can be a common cause for the error described in this question.

Answer 2

Try like this:

server.bind(("0.0.0.0", 6677)) 

Answer 3

When you bind localhost or 127.0.0.1, it means you can only connect to your service from local.

You cannot bind 10.0.0.1 because it not belong to you, you can only bind ip owned by your computer

You can bind 0.0.0.0 because it means all ip on your computer, so any ip can connect to your service if they can connect to any of your ip

Answer 4

This is not directly answering the question, but is a debugging direction in case above solutions failed.
When you are not on a native environment, let's say you are on a VM or WSL, the inside network might not be transparent to external computer due to NATing. So make sure you can ping the IP from wherever you are trying to bind. If not, then consider switching to the correct environment or consider network bridging. If you are looking for a WSL2 specific solution, you may try this link: Bridging WSL2 network adapter with Windows In Virtual Box you may change Network Adapter -> Attached To: Bridged Adapter. The other consideration is if you are trying to bind to a port <1023 you need admin privilege.