Changing the routing cost for a connection

IBM® Notes® routing assigns a routing cost to each connection and uses these costs to select the most efficient way to route mail from one server to another. The Router computes and stores information about these costs in its routing tables. If there is more than one possible route for mail to travel between the source server and the destination server for the message, the Router uses routing cost information in the tables to calculate the least-cost route for the message.

About this task

The Router uses information in Server, Domain, and Connection documents to create the routing tables. A LAN connection has low cost; a dialup modem connection has high cost. By default, each LAN connection has a cost of 1, while each dialup modem connection has a cost of 5.

Note: Support for dialup modem (X.PC) connections is available only in releases prior to IBM® Lotus® Domino® 8.5. You may continue to use Domino® 8.5 Administrator to configure and maintain modem support, but only on servers running pre-8.5 releases.

If server connections are disrupted or a network fails, the Router selects an alternate path and increases the cost for the path that failed.

How the Router chooses a route

The router chooses a route based on the following calculations:

  1. It calculates and selects the least-cost route.
  2. If the least-cost route fails -- for example, if there is no answer or if the network times out -- the Router increases the cost of the initial route by 1. For example, if a LAN connection between Server A and Server B initially has a cost of 1 but the connection fails during an attempted transfer, the Router increases the cost of that LAN connection between Server A and Server B to 2.
  3. The next time the Router tries to transfer mail between servers, it again looks for the least-cost route between those servers. If there is an alternate route that is equal in cost and requires fewer hops, the Router selects that alternate route. For example, if there are two paths between Server A and Server B, each with a total cost of 4, the Router examines the number of hops in each path. If one route requires three hops but the other requires only two hops, the Router uses the path that requires two hops because the costs are equal.

The Router resets the cost for a connection when:

  • The server receives an inbound connection from the failed server
  • The dynamic cost interval occurs
  • You stop and restart the Router

Overriding the default routing cost

About this task

You can override the default setting for the routing cost for a connection. You can change this setting only for connections between servers in different Notes® named networks. Change the default routing cost for a connection only if you are an experienced IBM® Domino® administrator. Improperly changing routing costs can create routing loops and disable the Router's selection of an alternate route.


  1. Make sure that you have already created the necessary Connection documents.
  2. From the Domino® Administrator, click the Configuration tab and expand the Messaging section.
  3. Click Connections.
  4. Select the Connection document for the server connection you want to configure, and click Edit Connection.
  5. Click the Replication/Routing tab.
  6. In the Routing cost field, enter a number from 1 to 10. The default is 1.
    The Router chooses connections with the smaller routing cost first; for example, the Router chooses a connection with a cost of 2 before choosing a connection with a cost of 3.
  7. Click Save & Close.


The change takes effect after the next Router configuration update. To put the new setting into effect immediately, reload the routing configuration.