Well, Redhat EL X.x is a propitiatory OS, and is expected
to work OK only when you have the paid Redhat account.
Then you have access to all the genuine Redhat packages.
And can install all packages with ' yum '.
You can find the real name for the OS with the commands :
.. and ..
Assuming you have Redhat EL 5.x :
The current libpcap packages are libpcap-0.9.4-14.el5.i386.rpm
If you have installed a random mix of packages found on the net,
there may appear some problems.
The free version of Redhat EL 5.4 is CentOS 5.4