XCON: Least-cost Routing DoesnÆt Take Open-retry State into Account in Routing Algorithm |
The information in this article applies to:
-
Microsoft Exchange Server, version 5.5
SYMPTOMS
When message transfer agent (MTA) least-cost routing is enabled, as
described in Knowledge Base article Q166567, the routing algorithm does not
take into account the open-retry state of the connector. Therefore, when a
message is sent to be re-routed, the normal load-balancing logic is used,
and the MTA tends to send the message back to the connector that is in the
retry state. Additionally, the way in which the MTA performs load balancing
now tends to favor the first selected connector in the early stages of
message delivery, and then this tapers off to a more equal ratio as message
flow and time increase.
For example, in the following scenario, there are three servers in two
sites:
Site #1, Server #1
Site #2, Server #2
Site #2, Server #3
and two X.400 Connectors:
Connector #1 between Server #1 and Server #2, cost of 1 and with least-
cost routing enabled.
Connector #2 between Server #1 and Server #3, cost of 1 and with least-
cost routing enabled.
- When messages are sent from Site #1 to Site #2, the messages should
load-balance over Connector #1 and Connector #2.
- If Server #2 is shut down and messages sent from Site #1 to Site #2,
messages should be sent over Connector #2 (after Connector #1 starts
open-retry).
CAUSE
The only scenario affected by the problem should be least-cost routing
where multiple links of equal lowest cost exist. The reason is that for
least-cost routing, the MTA does not filter connectors based on whether
they are in open-retry mode.
STATUS
Microsoft has confirmed this to be a problem in Microsoft Exchange Server
version 5.5. This problem has been corrected in the latest U.S. service
pack for Microsoft Exchange Server version 5.5. For information on
obtaining the service pack, query on the following word in the Microsoft
Knowledge Base (without the spaces):
S E R V P A C K
Keywords : XCON
Version : 5.5
Platform : winnt
Issue type : kbbug
