The accessibility of the server has always been one of the most important features of Notes. But server connections had a major limitation in their one-to-one nature -- mobile users could connect to only one server at a time; LAN-based users could connect only to servers supporting their workstation's network protocol. Passthru, introduced in Notes 4.0, overcame that limitation, bringing unprecedented flexibility to the connections between Notes clients and servers. Passthru is a process that runs on a server and establishes connections between users connected to that server and other servers. A passthru server can be a "stepping stone" between you and a destination server, even when that server is in a different domain or runs a different communication protocol.

This article will introduce you to passthru and how to set up passthru connections by creating Server Connection documents in your Personal Address Book. (Setting up a server for passthru is a necessary prerequisite, of course, and if you're an administrator, you should refer to the Domino Administration Help for more information on that process.)

The plusses of passthru
Passthru has made life easier for both mobile Notes users and Notes administrators. Before passthru, dialing up multiple Notes databases usually meant that you had to make multiple phone calls -- unless your administrator had grouped the most frequently used applications on a single modem-equipped server.

With passthru, you can make one dial-up connection using the X.PC protocol to a passthru server on a LAN and connect through it to other servers. The passthru server handles the translation between the dial-up protocol and the LAN protocol, and the address resolution for any servers that you request. You can go through more than one passthru server to get to your destination server, and you can connect to many servers without redialing, and have databases open on more than one server at once.



Passthru has similar advantages for LAN-based connections as well. A passthru server running multiple protocols can translate between dissimilar protocols, connecting a workstation running only TCP to databases on a server running only SPX, for example.

Passthru is not only more convenient for users, but it allows the most efficient deployment of network resources: Modem connections can be concentrated on one server machine to provide a single dial-in access point to the LAN, while databases can be distributed across many servers, running different protocols in different domains, in whatever configuration makes the most logical use of server capacity.

"Passthru was designed to be simple in the most common cases and flexible enough to handle the complex cases," says George Sprott, a senior developer at Iris who has worked extensively on passthru. But that flexibility has made configuring server connections more complex as well. Once the choice was simple: either LAN or dial-up. "In Notes V3, the algorithm used was that when you wanted to connect, Notes would try over the LAN and if that failed, it would look at the Connection document, and the only kind available was for dial-up connections," explains Sprott. "Then in V4 we added passthru, and that complicated things. It became clear that Connection documents had to be considered first." (Server Connection documents contain information Notes needs to find a path from a client to a server, and are stored in your Personal Address Book.)

Passthru servers and your Personal Address Book
The most common way of using a passthru server is as a default. You set a default passthru server by entering its name in the Passthru server field in a Location document. Notes uses the default passthru server when it can't find a path to your requested destination server by any other means (such as, by requesting an address from your home server or by using a Server Connection document.) For example, the following screen shows Saturn/Acme as the default passthru server for this location.



To access a passthru server different from the default server specified in your current Location document, you need to create a passthru Server Connection document in your Personal Address Book. (Creating a specific passthru Server Connection document in your Personal Address Book may also help speed up the Notes process of searching for a path to connect to a destination.) When you attempt to connect to a selected destination server, Notes looks first for a Server Connection document before using your default passthru server.

At first glance, the passthru Server Connection document may seem confusing, because it asks you to name both a destination server and a passthru server. It helps to remember that you are not defining a server as a passthru server, you are instructing Notes to route connections to the destination server through the specified passthru server. The passthru server you specify can be the same as your default passthru server, or a different one. For example, the following screen shows that Notes should use Sales/Acme to pass through connections to Venus/Acme.



An important point to remember is that the passthru Connection documents and Location documents choose only which server to use for passthru. They do not define how to connect the workstation to the passthru server. If you cannot directly connect to the passthru server over the LAN, you must create a separate Connection document to define the path to the passthru server.

Using passthru in Local Area Network connections
The Local Area Network connection is the simplest of the connection types because Notes requires very little setup to make a server connection on a LAN. And if all of your company's servers are in the same domain, a LAN connection is all you need. Notes will be able to connect to all the servers just by making name service requests to your home server, which will resolve the servers' addresses. You just need to make sure the home server name is properly provided in your Location document.

However, there are a couple of common cases where a name service request for a remote server won't produce a connection. One is when your workstation isn't running a protocol in common with the destination server. The other is when your company's servers are grouped in multiple domains.

In the case of a protocol mismatch, the default passthru server should be able to bridge the gap. Getting to the default passthru server may take some time, however, because Notes first exhausts all other connection possibilities. If you know that a server connection will require passthru, you may be able to speed up your connection by creating a passthru Connection document specifying the server you want to pass through.

Although sometimes you can make direct LAN connections to servers in another domain, if you can't, you can rely on passthru. You can then create a passthru Server Connection document in your Personal Address Book specifying the passthru server for accessing the servers in the other domain. You can use wildcard constructions such as "*/Acme" in the destination server field to specify that the passthru server be used to access any server in a particular domain. The passthru server can be in the local domain or in the foreign domain. If you can find out the default passthru server in the foreign domain, that may be the best one to use.

It may also help to create a LAN Server Connection document specifying what protocol and address to use to get to that passthru server, says Sprott. If you give the passthru Server Connection document a normal priority, connections to all servers in this domain will go through the passthru server. This has a high likelihood of success, but connecting through a passthru server could take longer, and the throughput could be lower than a direct connection, if one were possible. "An alternative," says Sprott, "is to give the passthru Server Connection document a low priority. This way Notes will try to connect to the server directly over the LAN first, and then if that fails, it will go the passthru route."

Using passthru with dial-up connections
A Notes client uses the X.PC protocol to communicate with a server through a COM port and a modem. If this is a passthru server, the client can connect to any server that the passthru server can connect to. When you make a dial-up connection, Notes automatically treats the server you connect to as your default passthru server, and attempts a passthru connection through it in the event that you can't connect to a destination server by any other means.

A passthru server is particularly useful if it is connected to a hunt group. A hunt group is a collection of telephone lines that can be accessed by a single external telephone number. Each call that comes in to that number is assigned to the next free line in the group.

Hunt groups have great advantages for Notes dial-up access. If a domain has heavy dial-up activity, it may require more than one passthru server to handle the load. Multiple passthru servers can be used together in a single hunt group, but in order to connect to any one of several passthru servers through a hunt group, the dial-up client must have a hunt group Server Connection document that specifies the hunt group name rather than a destination server. The same hunt group name should also appear in the Passthru server field of the Location document or in any passthru Connection documents that reference it. A hunt group Connection document is not required for a hunt group with a single passthru server. A simple modem Connection document will do in this case.

Using passthru with Internet connections
Another way to use passthru is for connecting to a destination server on your company's LAN over the Internet from a workstation dialed in to an Internet Service Provider. If there is a passthru server that is connected to the LAN and also to the Internet, you then pass through this server to open databases on company servers. This process has some prerequisites (you must have access to a passthru server with an Internet connection and an IP address and domain name) but it can have a very high payoff.

If the passthru server is available, and you have an Internet connection for your workstation, the steps in setting up the connection are straightforward:

• Create a new Internet Location document that enables the TCP port.
• In the Location document, set the passthru server name to the passthru server you've chosen.
• Create a Server Connection document that specifies Local Area Network as the connection type and TCP as the LAN port. Enter the name of the passthru server.
• Open the Advanced section. In the "Only from Location(s)", choose the Location you just created and add the host name or IP address of the destination server.

Copyright 1997 Iris Associates, Inc. All rights reserved.