Migrating to new ISP

[Carlomd]

Hello, we're pretty new to IP addressing, my company siged up for a mlppp or t3, so we're trying to migrate over our current network from the old ISP, our plan was to keep the current IP addresses of 208.36.7.xx and nat that with the new IP block from ATT (12.54.120.xx for servers), we have a Netscreen25 f/w. We also have VOIP system.

We were tried setting the old ip's on the f/w trust port and then using the gateway ip from ATT (untrust), it wouldn't let us use the old block, it only somehow works with private addresses. So we're trying to look at some options, should we use new IP's from ATT to change all the servers addresses, or will we be able to keep our old IP's to use with ATT's new ip's. Thanks in advanced.

[Collin Clark]

Since XO owns the 208.36.7.0 address space you will have to migrate all your NATs to the new 12.54.120.0 address space. Don't forget to change DNS too!

Hope that helps.

[Carlomd]

Thanks for the reply Collin, yeah we were hoping we can avoid downtime by keeping the old IP's, since they are just gonna be used internally, we thought it would work by using them internally as NAT and the new ATT ones outside. So basically we have to change the entire IP's to rfc1918, and MIP any servers to the ATT IP's for outside use.