ATM to Ethernet conversion

More old kit .....
We have a bunch of old Sun kit E4500, E450 etc that are currently running on ATM nic's and need to be put on the the onboard Ethernet ports....

Anyone know how to do this without downtime?

It'd be better if I can keep the original Ip Addresses though it may be possible to add a second IP address to the onboard port, in which case it sounds fairly straight forward, though wouldn't this also require a reboot?

Thanks in advance....

How much scheduled downtime could your environment handle?

I've been informed zero downtime is the preferred option :0/ ..... How much do you think I may need... Just a bounce?