How to install iftop?

iftop available in EPEL repository:

# rpm -ivh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm

You can either download the source code and compile the package yourself, or you can downloaded the binary package for your distribution.

Have a look at http://pkgs.repoforge.org/iftop/ as it provides binary packages for RHEL/CentOS and the source.

To install the binary package on CentOS-6 64-bit just do the following:

wget http://pkgs.repoforge.org/iftop/iftop-0.17-1.el6.rf.x86_64.rpm
rpm -ivh iftop-0.17-1.el6.rf.x86_64.rpm

For CentOS 7 (fully updated today), install from EPEL repository

yum install epel-release -y
yum install iftop -y

Not 100% sure, but I think earlier versions require downloading the EPEL repository and installing manually using rpm, then you can just "yum install iftop" (as per other answers)