Multiple Log-in Prompts for Sites in Different Zones for External Access

Hi, We have the following set up for out SharePoint sites that are accessible externally also.

Web Application 1 (default for portal) on port 80 and 443 (Extended into two zones)

- Intranet Zone for Intranet Portal - port 80 and 443 - url: https://portal.mycomp.com

- Custom Zone for Partner Portal - port 80 and 443 - url: https://partners.mycomp.com

Web Application 2 (default for my sites) on port 80 and 443 (Extended into one zone)

- Intranet Zone for My Sites - port 80 and 443 - url: https://my.mycomp.com

There are no issues with Partner portal as it is configured for form based authentication. Intranet portal and My Sites are configured for Windows authentication and work fine when accessed with in company network. Issue is that when users access the intranet portal from outside company network they gets log in prompt for for first time which is acceptable, but, when users clicks on My Site link on portal they are again getting log in prompt.

I searched and found this is due to different host headers etc. Now keeping all things same, how can we remove the double log-in prompt. Will it work if we change to Kerberos provider instead of NTLM or we need to use ADFS? Please suggest solution for this.

Thanks in advance,

Amit