Same URL for both sharepoint servers

Hi,

I am currently working on a SharePoint 2010 site.We do have 30 site collections for our web application.We are planning to migrate our app from SP 2010 to SP 2013.We are thinking to do it one by one site collection wise.But at same time we want to retain the same web application URL on both servers.

Please help me on this.

How can I achieve the same URL target on both SP 2010 and SP 2013 servers?