see: http://www-01.ibm.com/support/knowledgecenter/SSKTMJ_8.0.1/com.ibm.help.domino.admin.doc/DOC/H_SETTING_UP_A_SAMETIME_SERVER_FOR_DOMINO_WEB_ACCESS_IN_A_CLUSTERED_ENVIRONMENT_STEPS.html

Setting up Sametime and Domino Web Access in different domains

To set up a cross-domain configuration when the IBM^® Lotus^® Sametime^® server and the IBM^® Lotus^® Domino^® Web Access server are located in different domains:

Note Alternatively, you can configure users for Web single sign on (SSO) authentication. See the topic "Setting up the Web SSO Configuration document for more than one Domino Domain".

Another way to do this is to edit Configuration Settings document, Domino Web Access tab, and enter the Sametime server name in the in the field "Set an instant messaging server hostname for all Domino Web Access users." If you use this setting, you do not need to complete Step 5.

1. Cross certify both domains with each other. This step may be necessary only if the Sametime server uses Domino authentication instead of LDAP.
2. Configure Directory Assistance on the Sametime server as needed:
   • If Sametime uses native Domino authentication, then Directory Assistance must point to the Domino Web Access server, using the Notes protocol instead of LDAP.
   • If Sametime was installed to use LDAP, then Directory Assistance is configured automatically, and nothing further is necessary.
3. If you have set up single sign on (SSO), go to Step 4. If you do not have SSO set up, replicate STAuthS.nsf to the Domino Web Access Server (file name is case sensitive on UNIX^® servers).
4. Create a server document for the Sametime server in the Domino Directory of the Domino Web Access server, completing the fields below:
   • Server name
   • Domain name
   • Fully qualified Internet host name
   • Is this a Sametime server?
5. Enter the Sametime server name in the Sametime Server field of each Domino Web Access user's Person document.

Note If the Sametime server is configured using a port other than the default port, then the "Fully Qualified Hostname" field must contain hostname:port.

For complete information on working with multiple Sametime servers, see the IBM Lotus Sametime 7.5 Administrator's Guide, available at http://www.ibm.com/developerworks/lotus/documentation/sametime.