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Hub Transport Mail Flow Behavior - 23.Sep.2008 5:34:38 AM

Draconis

Posts: 116
Joined: 11.Sep.2008
From: Connecticut, USA
Status: offline

Hi Guys,

I just wanted to get more info regarding message handling between Hub Transport servers.

Lets say there are two scenarios:

********** SCENARIO 1 **********

Sites:
Site 1 - New York
Site 2 - New Jersey
Site 3 - Connecticut
Site 4 - Pennsylvannia

Site Links:
New York to New Jersey - Cost 10
New Jersey to Connecticut - Cost 5
Connecticut to Pennsylvannia - Cost 10
Pennsylvannia to New York - Cost 15
New York to Connecticut - Cost 20

I've been told that I should use Set-ADSite -Identity "New Jersey" -HubSiteEnabled:$true to ensure that messages between New York and Connecticut sites are routed through the New Jersey site. When I look up the cmdlet on Technet (http://technet.microsoft.com/en-us/library/bb124548(EXCHG.80).aspx), this is what they note:

By default, the Hub Transport servers that are located in Active Directory sites along the path between the source server and the destination server do not process or relay the messages in any way.

Then they also note,

When a hub site exists along the least cost routing path between two Hub Transport servers, the messages are routed to the hub site for processing before they are relayed to the destination server.

So my questions are these,

What is meant by routed to the hub site for processing?
What is done to the message itself when it is being processed?
What is meant by relayed?
Does this all mean that when it gets to that HubSite, the message header is just stamped saying this hub site got it? If so, it doesnt sound like any Hub Transport server would ever modify header information unless this cmdlet is specified to TRUE.

********** SCENARIO 2 **********
Minor Change: Cost for the Site Link between New York to Connecticut changed from 20 to 15.

Sites:
Site 1 - New York
Site 2 - New Jersey
Site 3 - Connecticut
Site 4 - Pennsylvannia

Site Links:
New York to New Jersey - Cost 10
New Jersey to Connecticut - Cost 5
Connecticut to Pennsylvannia - Cost 10
Pennsylvannia to New York - Cost 15
New York to Connecticut - Cost 15

So my questions are these,

After I enable the HubSite to TRUE for New Jersey, since the Total Cost is the same going from New York to New Jersey to Connecticut as the Cost from New York to Connecticut, does it mean that all mail flow will always go through the New Jersey Hub Transport server because it's a HUBSITE? What happens if the New Jersey Hub Transport server were to become unavailable due to the New Jersey site being down or the server being down? Does mailflow stop between New York and Connecticut or is the system smart enough to send it directly?

Sorry for asking so many questions, studying for these exams makes my brain hurt...I'm scheduled for my 70-237 Design after passing 70-236 Installation and I cant even understand a simple cmdlet...grrrrrr.

Thanks guys for your patience. :-)