Cannot assign requested address - possible causes

Question

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  amp 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

User · Accepted Answer

Maybe SO REUSEADDR helps here  http   www unixguide net network socketfaq 4 5 shtml

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

sysctl -w net ipv4 tcp timestamps 1 sysctl -w net ipv4 tcp tw recycle 1

[c] Cannot assign requested address - possible causes?

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