You should put the distro you use in your profile. Some distros do things differently. You may have a "/sbin/ifrenew-dhcp" program. If so "sudo /sbin/ifrenew-dhcp" will get a new lease from a dhcp server.
There is also the if-up <interface>" and "if-down <interface>" scripts.
On SuSE linux you can use rcnetwork:
Code:
Usage: /sbin/rcnetwork <action> [<config>] [<interface>] [-o <options>]
actions: start|stop|status|reload|force-reload|try-restart
restart|stop-all-dhcp-clients|restart-all-dhcp-clients
options: [on]boot,hotplug,manual,check,debug,fake,nm,netcontrol
type=<typelist>,skip=<skiplist>
typelist: space seperated list of interface types
skiplist: space seperated list of interfaces to skip for 'start'
