XCON: GWART Does Not Contain All Possible Routes

ID: Q243274

The information in this article applies to:

Microsoft Exchange Server, version 5.5

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

Keywords : exc55
Version : winnt:5.5
Platform : winnt
Issue type : kbinfo