IBM Token-Ring Adapter Features

Route Switching

This chapter describes the Route Switching feature of the IBM token-ring adapters.

Supported environments

History

Before the explosive growth in the use of Internet-based protocols, the 80/20 rule was followed when designing and deploying an IP-based network. This rule stated that the network should be designed on the assumption that 80% of network traffic would remain within the same subnet while 20% of network traffic would cross subnet boundaries. Maintaining the 80/20 rule allowed routers of that time to keep up with traffic flowing between subnets. With the explosive growth of the use of HTTP, that is, Web-based intranets and the Internet, the 80/20 rule can no longer be maintained.

As users jump from server to server on the Web they might jump from subnet to subnet, requiring almost all network activity to traverse the routers dividing the subnets. In addition, as network backbone technologies increase in speed, such as the move to 100-Mbps Token-Ring, the router bottleneck problem becomes even more of an issue.

Campus network architectures have been moving in two fundamental directions. The first is a continuation of a core networking architecture, with routers moving data between subnets, and the second is an edge networking architecture such as the IBM Switched Virtual Networking framework. In the area of performance improvements, efforts in the core networking model center around improving router performance, for example the recent interest in media-speed routers. By contrast, one of the main interests of the edge networking model is based on improving networking performance by distributing function away from a centralized, single-point-of-failure device.

Overview

Route Switching is IBM's approach to IP switching, or Layer 3 switching, that is actually a hybrid of both models. Route Switching still requires a centralized routing function in the network in order to provide the many functions that a router provides, except for the movement of traffic between subnets. With Route Switching, the traffic movement more closely follows the edge networking model.

The Route Switching feature of the IBM Token-Ring Adapters has been integrated within the device driver making installation and configuration as simple as upgrading the device driver. There are two modes of operation for Route Switching: client mode or peer mode. Client mode is the preferred mode. Route Switching is based on the Next Hop Routing Protocol (NHRP) standard from the Internet Engineering Task Force (IETF) and makes use of this standard when operating in either client or peer mode.

When Route Switching is operating in client mode an IBM Multiprotocol Switching Services (MSS) Server is required to perform the Route Switching server function. When in client mode, the enabled IP host issues requests to the IBM MSS Server for shortcut information for a remote IP host to which it is attempting to communicate. Once the shortcut information is received by the requesting client, subsequent traffic to the remote IP host is sent through the shortcut path instead of through the routed path. When Route Switching is operating in peer mode, the same request for shortcut information is sent directly through the routers to the remote IP host. If you install and configure Route Switching for peer mode on the remote host, the remote host sends a shortcut reply back to the requesting host. In either case, until the reply is received, the IP traffic will continue to be sent on the routed path.

In both situations, access control maintained by the router is not compromised. In the case of client mode, the MSS is also performing the routing function and will ensure that shortcut information is not supplied for a remote host that is not allowed to be reached. When in peer mode, the shortcut request goes through the router to the remote host. Therefore, if the requesting host is not permitted to communicate with the remote host, the request for a shortcut path will never be received by the remote host.

Route Switching can also be set to automatic mode. When in automatic mode Route Switching will initially operate in both client and peer mode. The first reply to a shortcut request that the host receives will determine the permanent mode of operation. For example, as soon as the adapter opens, Route Switching will begin attempting to discover the MSS Servers that exist in the network. At the same time, if IP traffic is being transmitted that is destined to a remote host not in this subnet, Route Switching will also begin sending shortcut requests to these remote IP hosts. If the requesting host receives a server discovery reply from an MSS Server, Route Switching will transition into client mode. If it receives a reply from a remote IP host, it will transition into peer mode.

Benefits

Route Switching can greatly improve performance of IP-based communications in networks with congested routers. The goal of Route Switching is to bypass the routing functions in an IP-based network without bypassing or undermining the other functions that a router provides, such as a firewall function and possibly broadcast containment. If the routers are creating a delay in the communication between IP hosts, Route Switching will eliminate that delay with just a simple upgrade of the LAN adapter device driver.

If a network currently has routing functions that are in need of performance improvements, Route Switching can add life to these routers and extend their usefulness indefinitely. In other words, with just the simple upgrade of device drivers for the IBM Token-Ring adapters, huge expenses for new higher performance routers can be deferred or completely eliminated.

Example scenarios

One-armed router

An environment in which Route Switching can be useful is a premise, or one-armed router, configuration. In this configuration there is one router at a location managing a multiple IP subnet network. All IP traffic between hosts on different subnets must go through this router. In this situation, two workstations might be on the same physical token ring, but from an IP perspective are configured to be on different IP subnets. This is very often the case when the two hosts belong to different business organizations or due simply to when they were installed. In this situation, traffic between these two workstations must leave one workstation, traverse the network all the way to the router, through the router, and then back across the network to the other workstation.

With Route Switching configured for peer mode, only the initial IP packets between these two hosts will be sent through the router. If in fact the two workstations are on the same ring, once the Route Switching function in the two workstations exchange their shortcut information, the traffic will only exist on that ring and will not be forwarded across any bridging functions. Suddenly, performance between these workstations is tremendously improved due to the removal of the router from the communications path. Also, the total number of packets flowing in the network is greatly reduced as well as the work load on the overburdened router.

Managing Route Switching with IBM LAN Adapter Management Agent

View the following values for the current configuration as well as the current status of Route Switching while using the IBM LAN Adapter Management Agent.

Route Switching Mode (Win32 only) Indicates the current state of the Route Switching function.

MSS Server Count Valid when Route Switching is operating in client mode. MSS Server count indicates the number of MSS Server interfaces that have responded to the request made by this computer to determine the Route Switching Servers in the network.

Maximum number of Cache Entries States the maximum number of cache entries available for use.

Current Number of Active Cache Entries Indicates the number of cache entries that are currently in use and contain valid shortcut information.

Switched Frame Count Count of the frames which have been sent using shortcut information when they otherwise would have been sent through a routed path. Observing this value changing over time indicates that Route Switching is operating.

Peer Holding Time (Win32 only) Valid when Route Switching is operating in peer or auto mode. Peer holding time indicates the cache entry holding time value which has been configured. This value is passed by this machine in replies to shortcut information.

System requirements

• Peer mode

  When Route Switching is operating in peer mode there are two requirements. First, IP hosts communicating with each other must have a Route Switching-enabled device driver installed and have Route Switching configured to either peer or auto mode. Second, there must be a Layer 2 path between the IP subnets.

• Client mode

  The client mode of operation is an asymmetric solution in terms of the two IP hosts communicating. This means that Route Switching Client can be configured on only one of the two hosts and benefits can be achieved. In order for Route Switching Client to operate, an IBM MSS properly configured for Route Switching is required.

  For more information about MSS, go to http://www.ibm.com/networking.

Installation and configuration

Installation and configuration information are particular to each adapter and are explained in the installation guide for your adapter. Go to http://www.ibm.com/networking and view the installation books for your adapter.

Route Switching parameters

The Route Switching function operates exactly the same way in every environment and accepts the same parameters in every environment. The following four parameters are used by the Route Switching function:

Route Switching mode

This parameter defines the mode in which the Route Switching function will operate. Route Switching can operate in client, peer, and auto modes, or it can be disabled.

In client mode, Route Switching will operate with an IBM MSS Server to provide the Route Switching function. In this mode of operation, the endstations will make requests of the server for shortcut information to remote IP hosts with which it is communicating.

In peer mode, Route Switching will operate without the existence of an IBM MSS Server. In this mode of operation, the end stations will make requests to the remote IP hosts to which it is communicating for its shortcut information. This mode of operation requires both IP host end stations involved in a conversation to have Route Switching Peer correctly installed and configured in order to operate. When in peer mode, the IP subnet mask must be passed to the Route Switching function.

In auto mode, Route Switching will initially operate in both modes. This means it will attempt to find an IBM MSS Server in the network as well as remote IP host end stations configured with Route Switching Peer. The first positive response it receives will determine the mode of operation of Route Switching for this end station.

For example, if an end station begins to operate in auto mode it will begin to attempt to discover IBM MSS Servers in the network. When IP traffic is transmitted to remote IP hosts residing on a different subnet, the Route Switching function will also send a shortcut request to the remote host in order to determine the shortcut information. If the remote host has configured Route Switching to peer or auto mode, it will respond to the request. If there are no IBM MSS Servers in the network, the end station will then enter into peer mode of operation. When in auto mode, the IP subnet mask must be passed to the Route Switching function.

If the machine is placed into a reduced-power state or is in some way suspended when configured in auto mode, it will return to auto mode when it returns to full power. This allows Route Switching to handle the changing of the network while an end station is not on the network.

Route Switching IP subnet mask

This parameter is required when Route Switching is operating in either peer or auto mode. It defines the IP subnet mask to which this adapter is connecting. This parameter is typically determined automatically. The Route Switching IP Subnet Mask must be in IP dotted-decimal address notation.

Route Switching peer holding time

This parameter is used when Route Switching is operating in either peer or auto mode. This value defines the amount of time that shortcut information is considered to be valid by the Route Switching function. When an end station provides its shortcut information to another requesting end station it includes this value along with the information. The requesting end station is allowed to use this shortcut information for this specified amount of time.

Route Switching cache table size

This parameter specifies the maximum number of entries that the Route Switching function can maintain at any given moment in time.

Each of the following installation and configuration sections assumes that your adapter is already installed and configured. The following sections define the steps required to enable Route Switching. If the adapter is not yet installed, refer to the Installation and Configuration manual for the adapter being used.

Windows 95, Windows 98, Windows NT, and Windows 2000

If you are using a Token-Ring PCI adapter on Windows 95 OSR2, Windows 98, Windows NT, or Windows 2000, use the instructions in Token-Ring PCI adapters (on Windows 95 OSR2, Windows 98, Windows NT, and Windows 2000) to set Route Switching parameters.

If you are using the IBM Turbo 16/4 Token-Ring PC Card 2, use the instructions in IBM Turbo 16/4 Token-Ring PC Card 2 to set Route Switching parameters.

Otherwise, use the instructions in this section.

To set the Route Switching parameters, perform the following steps:

1. Click Start > Settings > Control Panel.
2. Double-click IBM Token-Ring Adapter.
3. Select the adapter to be configured with Route Switching from the pull-down window at the top.
4. Click Route Switching.
5. Select Route Switch Mode of Operation in the upper box.
6. If you select either Peer Mode or Auto Mode, the IP Subnet (Network) Number parameter must be defined. If the Microsoft TCP/IP support is being used, the correct value for this parameter is automatically calculated and placed in the value field for this parameter. If this is not the case, then select the value field for this parameter and type the IP subnet mask for the subnet to which this adapter is connecting. You must enter this parameter in IP dotted-decimal notation.
7. Optionally, set the Peer Holding Time and the Cache Table Size to appropriate values based on the above descriptions.
8. Click OK.
9. Click Close.
10. Reboot the computer to apply the changes.

Token-Ring PCI adapters (on Windows 95 OSR2, Windows 98, Windows NT, and Windows 2000)

To set the Route Switching parameters, perform the following steps:

1. Click Start > Settings > Control Panel.
2. Double-click Network.
3. Select Adapters, then IBM Token-Ring PCI Family Adapter, and Properties.
4. Click the Route Switching tab.
5. If you select either Peer Mode or Auto Mode, the IP Subnet (Network) Number parameter must be defined. If the Microsoft TCP/IP support is being used, the correct value for this parameter is automatically calculated and placed in the value field for this parameter. If this is not the case, then select the value field for this parameter and type the IP subnet mask for the subnet to which this adapter is connecting. You must enter this parameter in IP dotted-decimal notation.
6. Optionally, set the Peer Holding Time and the Cache Table Size to appropriate values based on the above descriptions.
7. Click OK.
8. Click Close.
9. Reboot the computer to apply the changes.

IBM Turbo 16/4 Token-Ring PC Card 2

To set the Route Switching parameters, perform the following steps:

1. Click Start > Settings > Control Panel.
2. Double-click Network.
3. Select Adapters, then IBM Turbo 16/4 Token-Ring PC Card 2, and Properties.
4. Click the Route Switching tab.
5. If you select either Peer Mode or Auto Mode, the IP Subnet (Network) Number parameter must be defined. If the Microsoft TCP/IP support is being used, the correct value for this parameter is automatically calculated and placed in the value field for this parameter. If this is not the case, then select the value field for this parameter and type the IP subnet mask for the subnet to which this adapter is connecting. You must enter this parameter in IP dotted-decimal notation.
6. Optionally, set the Peer Holding Time and the Cache Table Size to appropriate values based on the above descriptions.
7. Click OK.
8. Click Close.
9. Reboot the computer to apply the changes.

Novell NetWare server

To set the Route Switching parameters, perform the following steps:

1. From the NetWare server console, type load install.
2. Select Driver Options.
3. Select Configure Network Drivers.
4. Select Select a driver.
5. Select the appropriate driver from the list of available drivers and press Enter.
6. Select Select/Modify driver parameters and protocols and press Enter.

For Route Switching configuration:

1. Using the arrow keys, move to the Parameters section, select Route Switching Mode, and press Enter.
2. Select either Client, Peer, or Auto for the parameter value and press Enter. You will see other Route Switching parameters in the parameter list.
3. Using the arrow keys, select Route Switching Table Size and enter a value from 16 to 1024.
4. If you selected Auto or Peer in step 2, use the arrow keys to select Route Switching Holding Time and enter a value from 2 to 20.
5. If you selected Auto or Peer in step 2, use the arrow keys to select Route Switching Subnet Mask and enter a valid IP subnet address for your network.

IBM LAN Client

To set the Route Switching parameters, perform the following steps:

1. Take one of the following actions:
   • If you have a token-ring PCI adapter that supports IBM LAN Client, run LCINST.EXE from the root directory of the adapter CD-ROM.
   • If you have the IBM Turbo 16/4 Token-Ring PC Card 2, run LCINST.EXE from the \LANCLNT directory of the adapter CD-ROM.
   • Run LCINST.EXE from the LAN Client diskettes or the self-extracting package file (LCPKG.EXE).

     Note:

     To install LCINST.EXE to a hard disk from the LAN Client diskettes, insert LAN Client diskette 1 in drive A and enter install.

2. Select the environment from the first IBM LAN Client Installation panel (Windows or Windows for Workgroups).
3. Select your adapter from the IBM LAN Client Adapter Selection panel.
4. Continue to the IBM LAN Client Application and Protocol Selection panel.
5. Select TCP/IP as one of the protocols to install and click OK.
6. Select the Route Switch tab on the IBM LAN Client Configuration panel.
7. Check Enable.
8. Select Auto, Peer, or Client mode.

   Note:

   If you select Auto or Peer, then you must enter an IP Address and a Subnet Mask on the TCP/IP configuration panel. You cannot enable DHCP.

9. Select Table Size and Holding Time values.

   Note:

   Holding Time is not valid if you selected client mode.

10. Click Install.

OS/2

To set the Route Switching parameters perform the following steps:

1. Double-click MPTS on the desktop.
2. Click OK.
3. Select LAN Adapters and Protocols and click Configure.
4. Select the name of the adapter in the current configuration section of the window and click Edit.
5. Scroll down through the configuration parameters until Route Switch Mode is displayed.
6. Make sure that the cursor is in the data entry portion of this parameter by either scrolling up or down or by clicking the data entry area.
7. To set the mode of Route Switching, type one of the following values: Client, Peer, or Auto.
8. Move the cursor to the data entry field for the IP Subnet Mask parameter.
9. Make sure that the cursor is in the data entry portion of this parameter by either scrolling up or down or by clicking the data entry area.
10. Enter the IP dotted-decimal value for the IP subnet network number to which this adapter is going to attach.
11. Click OK.
12. Click OK on the right side of the window.
13. Follow the instructions on the panels to exit MPTS.