TCP Socket listening but does not send ACK+SYN

Posted on 2006-11-30
Last Modified: 2013-11-29

I have a server that we are running several QA tests on. One test involves a java client that connects to a java server (all on the same machine). If I do a netstat , I can see that the Java server is running and listening on port 30041. When i kick off the test, I can see the client attempt a connection to the server's socket. The client socket sits there in the SYN SENT state but never appears to receive an ACK+SYN from the server socket. The client process eventually gives up and dies. Does anyone have any suggestions on how to troubleshoot this problem on a Linux box? The firewall and SELinux are turned off. What logs should I be looking at? I tried running TCPDUMP but that did not provide me with any useful info. Any help would be appreciated.
Question by:tmelo49
  • 4
  • 3

Accepted Solution

Trilotech earned 250 total points
ID: 18047560
Do you have multiple IP Addresses? Perhaps the client software is trying the wrong address (if you are using multiple addresses). This could mean a DNS issue if you are using hostnames.

Author Comment

ID: 18047705
Here is the tricky part that i forgot to mention, this particular server is actually a virtual OS through VMWare, but only has 1 IP and the DNS record appears fine (reverse lookup too). Even though it is a virtual OS, it functions as a completely independent OS. I really dont think the fact that it is a virtual OS is the cause of the problem. All other server/client processes talk just fine.

Expert Comment

ID: 18047809
Is it totally self contained in VMWare? Or is it an IP address that is accessible from the rest of your LAN?

If it is self contained and all other functions are working related to DNS and other networking services, then I would think the problem would be within the software. Perhaps a configuration error?

Check the documentation and perhaps contact the software developer.
Windows Server 2016: All you need to know

Learn about Hyper-V features that increase functionality and usability of Microsoft Windows Server 2016. Also, throughout this eBook, you’ll find some basic PowerShell examples that will help you leverage the scripts in your environments!


Author Comment

ID: 18047834
It is an IP that is accessible from the rest of the network.

Author Comment

ID: 18048488
I figured out the problem......incorrect hosts file entry for localhost .

Author Comment

ID: 18048511
Thanks Trilotech. You put me on the right path.

Expert Comment

ID: 18048524
No problem. Glad you got it!

Featured Post

How to improve team productivity

Quip adds documents, spreadsheets, and tasklists to your Slack experience
- Elevate ideas to Quip docs
- Share Quip docs in Slack
- Get notified of changes to your docs
- Available on iOS/Android/Desktop/Web
- Online/Offline

Join & Write a Comment

Suggested Solutions

Data center, now-a-days, is referred as the home of all the advanced technologies. In-fact, most of the businesses are now establishing their entire organizational structure around the IT capabilities.
Join Greg Farro and Ethan Banks from Packet Pushers ( and Greg Ross from Paessler ( for a discussion about smart network …
Viewers will learn how to properly install and use Secure Shell (SSH) to work on projects or homework remotely. Download Secure Shell: Follow basic installation instructions: Open Secure Shell and use "Quick Connect" to enter credentials includi…
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.

760 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

22 Experts available now in Live!

Get 1:1 Help Now