Q243274: XCON: GWART Does Not Contain All Possible Routes

Article: Q243274
Product(s): Microsoft Exchange
Version(s): winnt:5.5
Operating System(s): 
Keyword(s): exc55
Last Modified: 16-OCT-1999

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The information in this article applies to:

- Microsoft Exchange Server, version 5.5 
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SUMMARY
=======

Following a routing calculation, the Microsoft Exchange Server message transfer
agent (MTA) does not show all possible routes out of the site for a given
address space in the route table.

MORE INFORMATION
================

This behavior is by design. The Gateway Address Routing Tree (GWART) does not
contain all possible routes for a given address space. It does, however, contain
all possible routes out of the site which are unique in connector, address
space, and restriction.

To illustrate this GWART behavior using a basic example, consider when three
sites have Internet Mail Service, all with an address space of SMTP=*, as
follows:

  Route 1 - Site A, Internet Mail Service A, Address Space:SMTP=*
  Route 2 - Site B, Internet Mail Service B, Address Space:SMTP=*
  (Site B connected to Site A)
  Route 3 - Site C, Internet Mail Service C, Address Space:SMTP=*
  (Site C connected to Site B)

For Site A, the possible routes available in the GWART for the "SMTP=*" address
space are:

  Route 1 - Internet Mail Service A (SMTP=*)
  Route 2 - Internet Mail Service B (SMTP=*)

Because all routes are identical in respect to address space, and Route 3 is
higher cost (more than two hops), the GWART only includes Route 1 (because the
local route is always reflected) and Route 2 (because it is the shortest hop
path out of the site for the equivalent address space).

If Site C sets the Internet Mail Service C Address Space of SMTP:* to be Site
Restricted, there are two address spaces, one with a restriction and one
without. The possible routes that appear in the GWART on Site A at that point
are:

  Route 1 - Internet Mail Service A (SMTP=*)
  Route 2 - Internet Mail Service B (SMTP=*)
  Route 3 - Internet Mail Service C (SMTP=*, restricted)

Because the routes are different in restrictions, they are both included in the
GWART.

To expound further on this behavior, consider where you may have two different
connectors in the site which each then lead to four unique routes to get to
address space A. Then there are eight unique (non-looping) routes in total.
However, the GWART only shows two routes, one for each unique local connector,
with the lowest cost route from each local connector. If there are multiple
lowest cost routes of equal value, the GWART shows the shortest hop list for all
equally lowest cost routes.

Additional query words: missing

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Keywords          : exc55 
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : winnt:5.5
Issue type        : kbinfo

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