XCON: Route Selection Criteria
ID: Q193322
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The information in this article applies to:
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Microsoft Exchange Server, versions 4.0, 5.0, 5.5
SUMMARY
After the message transfer agent (MTA) has used the Gateway Address Routing
Table (GWART) to determine an appropriate list of possible connectors, the
MTA must then decide which connector is the best one to use. The following
criteria are processed in sequential elimination order to determine the
appropriate connector or connectors. Each connector or group of connectors
that meets the criteria for each step is passed to the next step for
testing.
- Eliminate any inbound connector that may have delivered the message
from another site.
- Select the connectors that are not at maximum retry. The selection
process checks two counters: Retry Count and Max Open Retries. The Retry
Count counter of the message is compared to the Max Open Retries counter of
the connector. Only connectors that are not at maximum pass this step.
- Select the connectors that will connect the soonest, also called
the activation schedule, which has four states:
- Active Now
- Will Become Active in the Future
- Never
- Remote Initiated
- Select the connectors that have tried to connect the fewest times. The
message Retry Count counter and the Max Open Retries counter are compared
again. This time, only the connectors that have been attempted the
fewest times are selected.
- Select the connectors that are not currently retrying a connection.
Each MTA maintains an Open Retry timer. This timer indicates how long
it has been since the MTA attempted a failed association. The MTA can
only know the Open Retry timer for any connectors on itself. Because
of that, if the connectors being considered are on different computers,
this step is bypassed.
- Select the connectors that have the lowest cost value assignment.
- Select local connectors over remote connectors. Local connectors
exist when the MTA that is processing the selection criteria has the
authorization to send the message directly to the remote site (for
example, an X.400 messaging bridgehead server). Remote connectors
require the MTA that is processing the selection criteria to pass the
message to a messaging bridgehead server before it can be passed to the
remote site.
MORE INFORMATION
Exchange Server version 4.0 Service Pack 4 and Exchange Server version 5.0 Service Pack 1 offer a
registry entry to alter the selection criteria.
For additional information about instructions on how to enable this feature, click the article number below
to view the article in the Microsoft Knowledge Base:
Q166567 XCON: How to Enable Lowest Cost Routes Only
This feature adds a new Use Lowest Cost Routes Only registry flag. If
this flag is set, the MTA always routes to the lowest cost link. The
one exception is that, if the activation schedule of the lower cost link is
currently inactive and the higher cost link is active, the rerouting is to the higher cost link.
NOTE: A route with an address space of * is chosen over an address
space of blank and overrides the cost value for connectors. The most
common occurrence of this is with the Internet Mail
Service (Internet Mail Connector in Exchange Server version 4.0).
Additional query words:
Keywords : XCON exc4 exc5 exc55
Version : winnt:4.0,5.0,5.5
Platform : winnt
Issue type : kbinfo
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