Open the IGEL Setup and browse to System->Firmware Customization->Custom Commands->Network Commands and enter here in Custom Command Network Final the following line:
ifconfig eth0 inet6 del ´ifconfig | grep "Scope:Link" | sed -e "s/^.*addr: //" -e "s/ .*//"´ or
ifconfig eth0 inet6 del ´ifconfig | grep "Scope:Link" | sed -e 's/^.*addr: //;s/ .*//'´
Try which one will work for you...
Please keep it like it is and make sure that any character is exactly the same otherwise it will not work!
After a reboot IPV6 is disabled.