Older versions of RedHat used to have "ifconfig ${DEVICE} ${IPADDR} netmask ${NETMASK} broadcast ${BROADCAST} ${ARP:+arp}" in /etc/sysconfig/network-scripts/ifup. Newer versions are missing the "${ARP:+arp}" part. This is needed by people who are using the ethertap device and want proper ARP activity. I can't see it effecting anyone else.
Um, how old is 'older' in this case? I don't see any traces of this in our CVS archive... :)
added in initscripts-4.65-1, which will be in the next Raw Hide release.