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Using Hub Transports in different AD sites


We are using Exchange 2007 SP1.

We have several AD sites - SiteA, SiteB, SiteC etc. Exchange servers are in SiteA and there are different Exchange servers per role.

I'm trying to figure out a question about how the Mailbox role connects with the Hub Transport. From what I understand, the Mailbox server has a list of Hub Transports in its local AD site.

Question1: How does it get this list? DSAccess process?

Question2: Let's say that I build a Hub Transport in SiteB. Currently, all other Exchange 2007 servers are in SiteA. If I was to lose my Hub Transport in SiteA, would the Mailbox server in SiteB be able to route mail via the Hub Transport in SiteB? Or does the Hub HAVE to be in the same AD site as the Mailbox server?

Question3: Assuming that the Hub HAS to be in the same site as the Mailbox server, is there a way to hardcode a secondary Hub, in a different AD site, for the Mailbox server to use?
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Jamie McKillopIT ManagerCommented:

1. This info is stored in AD. The mailbox server queries AD for the information

2. The mailbox server can only use a hub trnasport server in the same site. If you want redundancy, you need to deploy multiple hub transport servers in each site

3. No. See answer 2.

kam_ukAuthor Commented:


"The mailbox server queries AD for the information" - that is via DSAccess?
Jamie McKillopIT ManagerCommented:
Yes, that would be through DSAccess.

If you have a Exchange 2007 mailbox server in a Active Directory site, you also need a Hub Transport server. Each AD site wich contains a Exchange 2007 mailbox server role needs a hub transport server. If you have a Active Directory Site with a Mailbox Server and a hubtransport server, and the Hub transport server of that site would fail. The users connected to that mailbox server will be unable to send and recieve any mail. You cannot build Hub Transport  resiliance across two sites. If you need resiliance you need two hub transport servers in each site that contains a mailbox server role. The
Exchange mailbox server is aware of all the Exchange Hub Transport servers within his active directory site, so if one Hub Transport server would go done in a particualr site, it would outomatically use the next available hub transport server in that site. The hub transport server are aware of other Hub Transport servers in other sites, so it can pass on mail to the next hub to rout its mail to the recipient.
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