for SL4.4:

be root
  yum install denyhosts

=== for individual machines ===
  cd /usr/share/doc/denyhosts-2.2
  cp denyhosts.cfg-dist /etc/denyhosts.cfg
  vim /etc/denyhosts.cfg
 Edit as needed.
Luke suggests:
  PURGE_DENY = 5d
  BLOCK_SERVICE = ALL
  #BLOCK_SERVICE  = sshd
  SMTP_HOST = mail.vt.ed
  SMTP_FROM = DenyHosts <root@sysx4.arc.vt.edu>
though I don't do the last two i use:
  SMTP_HOST = localhost (default)
  ADMIN_EMAIL = root

  cp daemon-control-dist daemon-control
  vim daemon-control
  
  DENYHOSTS_CFG   = "/etc/denyhosts.cfg"
or  
  DENYHOSTS_CFG   = "/aoe/denyhosts-2.2/denyhosts.cfg"
  

  cd /etc/init.d/
  ln -s /usr/share/doc/denyhosts-2.2/daemon-control /etc/init.d/denyhosts
  ln -s /usr/share/doc/denyhosts-2.6/daemon-control /etc/init.d/denyhosts
  
=== for lab machines ===

use /aoe/denyhosts-2.2/ for the above two files and just add sym link to /etc/init.d
  cd /etc/init.d/
  ln -s /aoe/denyhosts-2.2/daemon-control /etc/init.d/denyhosts
  ln -s /aoe/denyhosts-2.6/daemon-control /etc/init.d/denyhosts

=== all machines ===

<del>Add to /etc/hosts.allow
  ALL: 172.16.1.  : allow
  ALL: 128.173.   : allow
  ALL: 198.82.    : allow
  ALL: .vt.edu    : allow
</del>

Run this to search logs for addresses
  python /usr/bin/denyhosts.py --file=/var/log/secure.1 --file=/var/log/secure.2 --file=/var/log/secure.3 --file=/var/log/secure.4 -c /aoe/denyhosts-2.2/denyhosts.cfg
or
  python /usr/bin/denyhosts.py --file=/var/log/secure.1 --file=/var/log/secure.2 --file=/var/log/secure.3 --file=/var/log/secure.4 -c /aoe/denyhosts-2.6/denyhosts.cfg

/usr/share/denyhosts/data/allowed-hosts
<file>
172.16.1.*
128.173.*.*
198.82.*.*
</file>

Set to start automatically
  chkconfig --add denyhosts
  chkconfig --list denyhosts
Start it manually at this time
  /etc/init.d/denyhosts start