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Exchange 2010 Hub Transport HA

I will lay out the configuration and then my questions.

Let's say I have two Active Directory sites, site A and Site B. I have two Exchange 2010 HT servers in each site for a total of 4 HT enterprise wide. As I understand it, the Microsoft Exchange Mail Submission service on mailbox servers automatically load balances connections among the HT servers within a site. Thus my questions relate to when failures occur.

If a HT server fails in Site A, will the mailbox servers simply use the second HT server in Site A? Logically it will, but just checking.

If both HT servers in Site A fail, will the mailbox servers cross to Site B and automatically begin connecting to the HT servers in Site B? I ask this question as I see references: “Hub Transport server to Hub Transport server communication inside an organization automatically load balances between available Hub Transport servers in the target Active Directory site.” What I do not see is anything answering what happens when the local HT servers both fail.

For external mail delivery (mail coming from the outside), can I and should I  use a load balancer to pass mail to any of these HT for HA? Are there any issues to using say a Foundry to LB among HTs or should I just have my Smart Host point to all HTs? Any ideas would be appreciated. Thanks all.

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dumamo
Asked:
dumamo
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1 Solution
 
BDoellefeldCommented:
Hi,

If a HT server fails in Site A, will the mailbox servers simply use the second HT server in Site A?
Yes

If both HT servers in Site A fail, will the mailbox servers cross to Site B and automatically begin connecting to the HT servers in Site B?
No

For external mail delivery (mail coming from the outside), can I and should I  use a load balancer to pass mail to any of these HT for HA?
You could and it depends on how much mail volume but quite often simply adding a second MX record pointing to the other Hub server will suffice.
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dumamoAuthor Commented:
Thanks you for the response.

To follow up, what are my options when two servers fail in one site? Is there a temporary remediation I can take to allow the mailbox servers to route mail through site B HT servers or am I simply dead in the water at that point? Could I somehow use the Foundry to load balance all 4 HT servers so Exhcnage could talk to any HT?

Is the site boundary the issue? I have found with CAS servers that Outlook clients are unable to talk to a CAS server in another site directly, they can only be referred to one by the locla CAS server. Is this the same with HT and mailbox servers in that they cannot talk to HT servers in another site at all?

Thanks!
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BDoellefeldCommented:
Hi there,

To follow up, what are my options when two servers fail in one site?
Really the only options are recovering one of the servers or adding a new server. If your in a position where you feel that losing the both servers at the same time is a real possibility, be it environment or some other factor, you should work to remedy those issues. If all HT servers in the AD site are unavailable, messages will be queued until a HT server becomes available again or the messages expire.

I have see a couple people try some different tricks, mainly trying to trick Exchange by adding remote HT servers into the the local AD site. Mixed results there, bandwidth issues, routing issues, etc.

Is there a temporary remediation I can take to allow the mailbox servers to route mail through site B HT servers or am I simply dead in the water at that point?
The mailbox servers won't talk across the site.

Could I somehow use the Foundry to load balance all 4 HT servers so Exhcnage could talk to any HT?
If you did this it is important to only load balance inbound SMTP traffic or traffic from non-Exchange sources. Nothing else is supported.

Is the site boundary the issue? I have found with CAS servers that Outlook clients are unable to talk to a CAS server in another site directly, they can only be referred to one by the locla CAS server. Is this the same with HT and mailbox servers in that they cannot talk to HT servers in another site at all?
Yes, the boundary is the site. The HT servers will talk to each other cross site but a mailbox server cannot talk to another sites HT server.

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