Amazing solutions for the oserror errno 99 cannot assign requested address error

Question

I get the error message:

*** Start Block *** 
errno99: cannot assign requested address

Has anyone ever faced this problem? How to troubleshoot the “oserror errno 99 cannot assign requested address.” The problem appears when I try to operate the following program:

#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()

hdtutoria · Accepted Answer

The cause: It's complaining about a problem with the IP address rather than the port. When you bind localhost or 127.0.0.1, you can only connect to your service from local. You can't bind 10.0.0.1 because it's not yours; you can only bind IP addresses that belong to your computer. Solution: Making everything become basic and perhaps you would like to test things below:

import socket
server = socket.socket()
server.bind(("10.0.0.1", 6677))
server.listen(4)
client_socket, client_address = server.accept()
print(client_address, "has connected")
while True:
    recvieved_data = client_socket.recv(1024)
    print(recvieved_data)

Julia Guillard · Answer

This error will also be displayed if the Docker container is not actively serving the port.

If you request a local URL that isn't served by a host that has no listening/bound port, you will get a No connection could be made because the target machine actively refused it error. If you create a container that binds the port but no server is running within it, requests to that port from localhost will be returned as:

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

This error and the behavior described above can be reproduced as follows:

Create a dummy container ( Note: This will pull the Python image from if it is not available locally ).

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

For [Errno 0] Error, you will need to enter a Python Console on host. [Errno 99] Cannot assign requested address will allow you to access a Python Console on the Container by calling:

docker exec -it -u 0 serv1 python

In either case, call:

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

I decided to treat these errors as No connection could be made because the target machine actively refused it equivalents rather than try to fix them - though please let me know if this is a bad idea.

This one took me over a whole day to figure out. All resources and answers that I could find on [Errno 99] Cannot assign requested address pointed in the right direction: binding to an occupied port; connecting to an invalid address; sysctl conflicts; docker network issues; TIME_WAIT being wrong, and many other things. This answer is not a direct answer to your question, but it could be a common cause of the error that you are describing in the question.

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Amazing solutions for the oserror errno 99 cannot assign requested address error