Unable to install NS2 due to the X Library problem

When I tried to install NS2 on Red Hat, it shows that

checking for tclcl.h... -I../tclcl-1.19
checking for libtclcl... -L../tclcl-1.19 -ltclcl
checking for tcl2c++... ../tclcl-1.19
checking for X11 header files
checking for X11 library archive
checking for XOpenDisplay in -lX11... no
can't find X library
Ns configuration failed! Exiting ...
Please check http://www.isi.edu/nsnam/ns/ns-problems.html
for common problems and bug fixes.

How to cope with the shortage of X library?
If we use cygwin instead of RedHat to install ns2, it still lacks of package xorg-x11-bin and even worse the new version of Cygwin no longer supports xorg-x11-bin.


Since there exist some problem when installing NS2 in Red Hat and Cygwin. an workaround solution is to install NS2 in Ubuntu, which is more promising as shown at
http://c-perl-programming.blogspot.com/2009/04/ns2-installation-in-linux-ubuntu.html