Hi Jeff,
Thanks for your reply.
I had added only the first 8 modules in httpd.conf. Remaining modules were added later only when I started facing this problem. Reducing the number of modules back to 8 does not make any difference with respect to this issue. With these 8 modules httpd worked fine with port 80. The problem started when I tried adding additional ports. Adding more ports is need of the hour. I can not escape it. I have run strace with "follow the fork" option (rather than single process). There are only 4 processess to follow. strace output did not help. It does not indicate any error condition as such. I can make it run as a single process by running httpd with -X option in foreground. But I am not sure whether that is going to help. Anyway, I will try that.

On Wed, Oct 10, 2012 at 6:47 PM, Jeff Trawick <trawick@gmail.com> wrote:
On Wed, Oct 10, 2012 at 7:55 AM, Jitesh Verma <jitesh.verma@gmail.com> wrote:
> Hi List,
> We have ported httpd-2.4.2 to a network embedded box running Linux on Xscale
> hardware. We have two modules of our own to handle XML requests from our
> Applets. We have added all the 80 odd .so modules (that get built with
> default "configure" settings) in httpd.conf.
> We are able to access the box's GUI/Applets with "Listen 80" directive in
> the httpd.conf.
> However, when we add another directive "Listen 9000" to httpd.conf, httpd
> does not respond to HTTP request sent to port 80. The following requests
> from Internet Explorer fails to get any response from httpd:
> Wireshark packet trace indicates that the request packet is correctly sent
> to TCP port 80 when request is sent from browser.
> However, the outgoing packet is missing from the packet trace. It seems
> httpd did not generate any response (not even "File not found" response).
> "netstat -tnlp" command shows httpd listening on both TCP port 80 and 9000.
> /var/log/access_log indicates that the incoming packet reached httpd.
> Gateway/firewall data indicates that both TCP ports 80 and 9000 are open in
> both the directions (incoming and outgoing).
> The moment additional "Listen 9000" directive is removed from httpd.conf,
> httpd starts working fine (starts serving request).
> We have enabled and configured "debugging" and "loggers" modules. Still,
> /var/log/error_log and /var/log/messages do not show any error or warning.
> We thought adding another "Listen" directive to httpd.conf is a child's
> play, but it seems to be a humongous task.
> Are we missing something? Am I doing something wrong?? Is it a bug??? Can
> someone help in this forum? How to debug this issue?
> Please find attached httpd.conf and configure wrapper script
> (configure.wrapper) used for configuring and building httpd and its
> components.
> Thanks,
> Jitesh

users@httpd.apache.org is a better mailing list for this.

A few things to start with...

Get unnecessary modules out of the configuration to simplify
logging/potential problems.
See what is logged with LogLevel trace8.
Configure the MPM to use a single child process to handle requests,
and run strace against that.

Born in Roswell... married an alien...