[c] Cannot assign requested address - possible causes?

I have a program that consists of a master server and distributed slave servers. The slave servers send status updates to the server, and if the server hasn't heard from a specific slave in a fixed period, it marks the slave as down. This is happening consistently.

From inspecting logs, I have found that the slave is only able to send one status update to the server, and then is never able to send another update, always failing on the call to connect() "Cannot assign requested address (99).

Oddly enough, the slave is able to send several other updates to the server, and all of the connections are happening on the same port. It seems that the most common cause of this failure is that connections are left open, but I'm having trouble finding anything left open. Are there other possible explanations?

To clarify, here's how I'm connecting:

struct sockaddr *sa; // parameter
size_t           sa_size; //parameter
int              i = 1;
int              stream;

stream = socket(AF_INET,SOCK_STREAM,0);
setsockopt(stream,SOL_SOCKET,SO_REUSEADDR,&i,sizeof(i));
bindresvport(stream,NULL);
connect(stream,sa,sa_size);

This code is in a function to obtain a connection to another server, and a failure on any of those 4 calls causes the function to fail.

This question is related to c sockets tcp errno

The answer is


this is just a shot in the dark : when you call connect without a bind first, the system allocates your local port, and if you have multiple threads connecting and disconnecting it could possibly try to allocate a port already in use. the kernel source file inet_connection_sock.c hints at this condition. just as an experiment try doing a bind to a local port first, making sure each bind/connect uses a different local port number.


Okay, my problem wasn't the port, but the binding address. My server has an internal address (10.0.0.4) and an external address (52.175.223.XX). When I tried connecting with:

$sock = @stream_socket_server('tcp://52.175.223.XX:123', $errNo, $errStr, STREAM_SERVER_BIND|STREAM_SERVER_LISTEN);

It failed because the local socket was 10.0.0.4 and not the external 52.175.223.XX. You can checkout the local available interfaces with sudo ifconfig.


sysctl -w net.ipv4.tcp_timestamps=1
sysctl -w net.ipv4.tcp_tw_recycle=1

It turns out that the problem really was that the address was busy - the busyness was caused by some other problems in how we are handling network communications. Your inputs have helped me figure this out. Thank you.

EDIT: to be specific, the problems in handling our network communications were that these status updates would be constantly re-sent if the first failed. It was only a matter of time until we had every distributed slave trying to send its status update at the same time, which was over-saturating our network.


Examples related to c

conflicting types for 'outchar' Can't compile C program on a Mac after upgrade to Mojave Program to find largest and second largest number in array Prime numbers between 1 to 100 in C Programming Language In c, in bool, true == 1 and false == 0? How I can print to stderr in C? Visual Studio Code includePath "error: assignment to expression with array type error" when I assign a struct field (C) Compiling an application for use in highly radioactive environments How can you print multiple variables inside a string using printf?

Examples related to sockets

JS file gets a net::ERR_ABORTED 404 (Not Found) mysqld_safe Directory '/var/run/mysqld' for UNIX socket file don't exists WebSocket connection failed: Error during WebSocket handshake: Unexpected response code: 400 TypeError: a bytes-like object is required, not 'str' Failed: Error in connection establishment: net::ERR_CONNECTION_REFUSED No connection could be made because the target machine actively refused it 127.0.0.1 Sending a file over TCP sockets in Python socket connect() vs bind() java.net.SocketException: Connection reset by peer: socket write error When serving a file How do I use setsockopt(SO_REUSEADDR)?

Examples related to tcp

What does "app.run(host='0.0.0.0') " mean in Flask What is the difference between HTTP 1.1 and HTTP 2.0? Sending a file over TCP sockets in Python Telnet is not recognized as internal or external command How to open port in Linux adb connection over tcp not working now Understanding [TCP ACKed unseen segment] [TCP Previous segment not captured] How do I debug error ECONNRESET in Node.js? Differences between TCP sockets and web sockets, one more time Is SMTP based on TCP or UDP?

Examples related to errno

Error in Python IOError: [Errno 2] No such file or directory: 'data.csv' MySQL: Error dropping database (errno 13; errno 17; errno 39) Python socket.error: [Errno 111] Connection refused How to create a file in Ruby Cannot assign requested address - possible causes? Python [Errno 98] Address already in use How to know what the 'errno' means?