How to compile NS2 on 64-bit System

When compiling NS-2.33 on a 64-bit CPU system, I got following error message from linker:
"skipping incompatible libXext.so when searching for -lXext"
cannot found libXext

The reason is the default directory in ns2 to look for libXext is /usr/X11R6/lib, where the 32-bit libXext is located. On a 63-bit system, we should change the directory to /usr/X11R6/lib64/. This can be done with a single command:

grep -rl "/usr/X11R6/lib" * | xargs sed -i -e 's/\/usr\/X11R6\/lib/\/usr\/X11R6\/lib64/'

Change current dir to ns-all-in-one-2.33 and execute the aboe command and run ./install. Then ns2 will be successfully compiled.

NOTE: the command should be run only once, otherwise there would be errors.