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Cisco IOS Terminal Services Configuration Guide, Release 12.2
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About Cisco IOS Software Documentation
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Using Cisco IOS Software
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Terminal Services Overview
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Configuring Terminal Operating Characteristics for Dial-In Sessions
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Configuring Dial-In Terminal Services
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Configuring AppleTalk Remote Access
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Configuring Support for NASI Clients to Access Network Resources
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Configuring the Cisco PAD Facility for X.25 Connections
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Configuring Protocol Translation and Virtual Asynchronous Devices
- Appendixes
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Table Of Contents
Configuring Dial-In Terminal Services
Dial-In Terminal Service Overview
Telnet and rlogin Configuration Task List
Configuring Telnet and UNIX rlogin
Making Telnet and UNIX rlogin Connections
Using UNIX Style Syntax for rlogin Connections
Telnet Connection Without and With Messages Suppressed Example
rlogin UNIX-Style Syntax Example
Switch Between Telnet and rlogin Sessions Example
List Supported Telnet Commands Example
Using Cisco DialOut for Telnet Connections
Stream TCP Autocommand Procedure
LAT Sessions and Connection Support
Connecting a VMS Host Using LAT
VMS Version 5.4 or Earlier System
VMS Version 5.5 or Later System
Port Names When Configuring a LAT Printer
Configuring Basic LAT Services
Controlling Service Announcements and Service Solicitation
Enabling Remote LAT Modification
Monitoring and Maintaining LAT Connections
LAT Configuration and Connection Examples
LAT Service with Selected Group Codes Example
Displaying LAT Services on the Same LAN Example
Establishing an Outbound LAT Session Example
Logically Partitioning LAT Services by Terminal Line Example
Associating a Rotary Group with a Service Example
Using the Default Terminal Emulation File to Connect
Copying a Sample Terminal Emulation File
TN3270 Configuration Task List
Configuring TN3270 Connections
TN3270 Configuration and Connection Examples
Custom Terminal Emulation File Example
Custom Keyboard Emulation File Example
Line Specification for a Custom Emulation Example
XRemote Configuration Task List
Selecting Fonts for X Terminal Applications
Accessing Nonresident Fonts Using TFTP
Connecting Through Automatic Session Startup with an XDMCP Server
Connecting Through Automatic Session Startup with a DECwindows Login via LAT
Connecting Through Manual XRemote Session Startup
Connecting to the Remote Host Computer
Setting the Location of the X Display
Establishing XRemote Sessions Between Servers
Monitoring XRemote Connections
XRemote Configuration and Connection Examples
Standard XRemote Configuration Example
Connecting Through Automatic Session Startup with XDMCP Server Example
Connecting Through Automatic Session Startup with DECwindows Login via LAT Example
Enabling XRemote Manually Example
Connecting an X Display Terminal Example
Making XRemote Connections Between Servers Example
Configuring Dial-In Terminal Services
This chapter describes how to configure support for asynchronous character stream calls running Telnet, rlogin, local-area transport (LAT), XRemote, or TN3270. It includes the following main sections:
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Dial-In Terminal Service Overview
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For a complete description of the dial-in terminal services commands in this chapter, refer to the Cisco IOS Terminal Services Command Reference, Release 12.2. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
Dial-In Terminal Service Overview
Inbound asynchronous character stream calls are routed to virtual terminal lines and virtual asynchronous interfaces, which are used to terminate incoming character steams that do not share a physical connection with the access server or router (such as a physical interface). A virtual asynchronous interface is the place where inbound Telnet, LAT, V.120, TN3270, and packet assembler/disassembler (PAD) calls or sessions terminate on the router. Virtual terminal lines are used for attaching to the router in a nonphysical way.
Configuring support for terminal service connections means enabling network devices running the same protocol to connect across a LAN or WAN through network and terminal-emulation software.
The following sections describe how to configure these supported dial-in terminal services:
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Each section provides examples of how to configure and connect to a terminal service.
Configuring Telnet and rlogin
Telnet and rlogin are protocols that enable TCP/IP connections to a host. Telnet, a virtual terminal protocol that is part of the TCP/IP protocol suite, is the more widely used protocol. The rlogin protocol is a remote login service developed for the Berkeley Software Distribution (BSD) UNIX system. It provides better control and output suppression than Telnet, but can only be used when the host (typically, a UNIX system) supports rlogin. The Cisco IOS implementation of rlogin does not subscribe to the rlogin "trusted host" model. That is, a user cannot automatically log in to a UNIX system from the router, but must provide a user ID and a password for each connection.
Telnet allows a user at one site to establish a TCP connection to a login server at another site, then passes the keystrokes from one system to the other. Telnet can accept either an IP address or a domain name as the remote system address. In short, Telnet offers three main services:
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The Cisco implementation of Telnet supports the following Telnet options:
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Telnet and rlogin Configuration Task List
To configure Telnet and rlogin, perform the tasks in the following sections:
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The section "Monitoring TCP/IP Connections" later in this chapter provides tasks for maintaining TCP/IP connections.
Configuring Telnet and UNIX rlogin
To configure support for Telnet or rlogin calls, use the following commands beginning in line configuration mode.
The telnet speed command sets the line speed to match line speeds on remote systems in reverse Telnet, on host machines hooked up to an access server or router to access the network, or on a group of console lines hooked up to the access server or router when disparate line speeds are in use at the local and remote ends of the connection. Line speed negotiation adheres to the Remote Flow Control option, defined in RFC 1080.
The telnet refuse-negotiations command suppresses negotiation of the Telnet Remote Echo and Suppress Go Ahead options.
The telnet transparent command is useful for coping with different interpretations of end-of-line handling in the Telnet protocol specification.
The telnet sync-on-break command sets the line to cause a reverse Telnet line to send a Telnet Synchronize signal when it receives a Telnet BREAK signal. The Telnet Synchronize signal clears the data path, but the line still interprets incoming commands.
Enter the telnet break-on-ip command to control the translation of Telnet Interrupt-Process commands into X.25 BREAK indications, and to work around the following situations:
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When the telnet break-on-ip command is used with a correctly operating host, Cisco IOS software implements the Telnet Synchronize and Abort Output signals, which can stop output within one packet worth of data from the time the user types the interrupt character. Enter the ip tcp chunk-size command to configure a faster response to user interrupt characters. Changing the number of characters output, or chunk size, affects neither the size of the packet used nor the TCP window size, either of which would cause serious efficiency problems for the remote host and for the access server or router. Instead, the system software checks the Telnet status after the number of characters specified, causing only a relatively minor performance loss.
Use the ip alias command to configure connections to an IP address to act identically to connections made to the primary IP address of the server on the TCP port. A user trying to connect is connected to the first free line in a rotary group using the Telnet protocol.
With the login-string command options, you can set a pause, prevent a user from issuing commands during a pause, send a BREAK character, and use a percent sign (%) in the login string. The busy-message command and login-string command are only useful with two-step protocol translation sessions. For more information about protocol translation, see the chapter "Configuring Protocol Translation and Virtual Asynchronous Devices" in this publication.
For actual sample configurations on how to configure Telnet and rlogin, see the section "Telnet and rlogin Examples" later in this chapter.
Making Telnet and UNIX rlogin Connections
To provide Telnet and rlogin connection capabilities, use the following commands in EXEC mode:
Step 1
Router> connect host [port] [keyword]
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Router> telnet host [port] [keyword]
Logs in to a host that supports Telnet. Refer to the descriptions for the connect and telnet commands in the Cisco IOS Terminal Services Command Reference, Release 12.2, for a list of supported keywords.1
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Router> show hosts
Displays a list of available hosts.
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Router> show tcp
Displays the status of all TCP connections.
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Ctrl^
Logs out of the host by entering the default escape sequence.2
Step 5
Choose from the following list of escape sequences, according to your task:
Press Ctrl^ b if your task is to break.
Press Ctrl^ c if your task is to interrupt a process (IP).
Press Ctrl^ h if your task is to erase a character (EC).
Press Ctrl^ o if your task is to abort an output display (AO).
Press Ctrl^ t if your task is to confirm you are at the host.
Press Ctrl^ u if your task is to erase a line (EL).Logs out of the host by entering a special escape sequence.2 These special Telnet sequences map generic terminal control functions to operating system-specific functions.
Step 6
Ctrl^ ?
Lists the available Telnet commands at any time during the active Telnet session.2
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exit
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logout
Exits a Telnet or rlogin session.
1 Cisco IOS software provides a robust collection of connection options. The options allow for enhanced sessions allowing, for example, encrypted sessions, Kerberos login, and File Transfer Protocol and World Wide Web connections. Additionally, it is possible to suppress system messages, including IP addresses and server names, displayed during session connection and disconnection. This function allows transparent TCP connections and can be useful when an asynchronous tunnel connection is being made.
2 Press and hold the Ctrl and Shift keys while pressing the 6 key. You can enter the command character as you hold down the Ctrl key or with Ctrl released; you can enter the command characters as either uppercase or lowercase letters.
With the Cisco IOS implementation of TCP/IP, you are not required to enter the connect or telnet commands to establish a Telnet connection. You can just enter the learned host name as long as the host name is different from a command word for the router. Telnet must be the default (you can make it the default with the transport preferred command). Use the show hosts EXEC command to display a list of the available hosts. Use the show tcp EXEC command to display the status of all TCP connections. The Cisco IOS software assigns a logical name to each connection, and several commands use these names to identify connections. The logical name is the same as the host name, unless that name is already in use or you change the connection name with the name-connection EXEC command. If the name is already in use, the Cisco IOS software assigns a null name to the connection. For an example of making a Telnet connection, see the section "Telnet and rlogin Examples" later in this chapter.
After you enter the rlogin command, you can have several concurrent rlogin connections open and switch between them. To open a new connection, exit the current connection by entering the escape sequence (Ctrl-Shift-6 then x [Ctrl^x] by default) to return to the system command prompt, then open a new connection. For an example of making an rlogin connection or switching between connections, see the sections "rlogin Connection Example" or "Switch Between Telnet and rlogin Sessions Example" later in this chapter.
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Using UNIX Style Syntax for rlogin Connections
The rlogin command supports the standard BSD UNIX -l option. Before this addition was introduced, the rlogin command allowed remote users to log in using the /user username option, which was not compatible with the standard UNIX rlogin -l username option.
This feature is supported on all of Cisco TCP/IP-enabled routers and access servers.
To set up this UNIX feature, use one of the following the following commands in EXEC mode:
When you are done with the UNIX session, use the exit command to end it.
Monitoring TCP/IP Connections
To display the status of a TCP connection or view a summary of the TCP connection endpoints in the system, use the following commands in user EXEC mode:
Router> show tcp [line-number]
Displays the status of a TCP connection.
Router> show tcp brief [all]
Displays a summary of the TCP connection endpoints in the system.
Telnet and rlogin Examples
This section provides the following examples:
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Telnet Connection Example
The following example establishes a telnet connection to a host named server1 and specifies vt100 as the terminal type for the session:
Router> telnet server1 /terminal-type vt100
The following example connects to a host with logical name host1:
Router> host1Telnet Connection Without and With Messages Suppressed Example
The following examples show how to suppress the onscreen messages displayed during login and logout of a Telnet session.
The following example shows the messages displayed when a connection is made without using the optional /quiet keyword with the telnet EXEC command to suppress messages from the operating system:
Router# telnet Server3Translating "Server3"...domain server (172.18.89.42) [OK]Trying Server3--Server3.cisco.com (172.18.89.42)... OpenKerberos: No default realm defined for Kerberos!login: User2Password:Welcome to OpenVMS VAX version V6.1 on node CRAWLast interactive login on Tuesday, 15-DEC-1998 11:01Last non-interactive login on Sunday, 3-JAN-1999 22:32Server3) logoutUser2 logged out at 16-FEB-2000 09:38:27.85[Connection to Server3 closed by foreign host]Router#The following example shows the limited messages displayed when connection is made using the optional /quiet keyword:
Router# telnet Server3 /quietlogin: User2Password:Welcome to OpenVMS VAX version V6.1 on node CRAWLast interactive login on Tuesday, 15-DEC-1998 11:01Last non-interactive login on Sunday, 3-JAN-1999 22:32Server3) logoutUser2 logged out at 16-FEB-2000 09:38:27.85Router#The /quiet keyword is useful for making transparent connections during asynchronous tunnel connections. The keyword can be used with any of the EXEC connection commands—connect, telnet, and rlogin.
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rlogin Connection Example
The following example makes an rlogin connection to a host at address 172.31.21.2 and enables the message mode for debugging:
Router> rlogin 172.31.21.2 debugrlogin UNIX-Style Syntax Example
The following example illustrates how a user named jsmith can use the rlogin ? help command and the debug mode to establish and troubleshoot a remote connection to the host named Alviso:
Router> rlogin ?WORD IP address or hostname of a remote systemRouter> rlogin Alviso ?-l Specify remote username/user Specify remote usernamedebug Enable rlogin debugging output<cr>Router> rlogin Alviso -l ?WORD Remote user nameRouter> rlogin Alviso -l jsmith ?debug Enable rlogin debugging output<cr>Router> rlogin Alviso -l jsmith debugSwitch Between Telnet and rlogin Sessions Example
You can switch between sessions by escaping one session and resuming a previously opened session. The following example shows how to escape out of a connection to the host named host1 and to resume connection 2. You escape out of the current session and return to the EXEC prompt by entering the command sequence Ctrl-Shift-6 then x. Resume the connection with the resume command.
host1% ^^XRouter> resume 2You can omit the command name and simply enter the connection number to resume that connection. The following example illustrates how to resume connection 3:
Router> 3To list all the open sessions associated with the current terminal line, use the where command.
List Supported Telnet Commands Example
At any time during an active Telnet session, you can list the Telnet commands by pressing the escape sequence keys (by default Ctrl-Shift-6) followed by a question mark at the system prompt:
Ctrl-^ ?A sample of this list follows:
Router> ^^?[Special telnet escape help]^^B sends telnet BREAK^^C sends telnet IP^^H sends telnet EC^^O sends telnet AO^^T sends telnet AYT^^U sends telnet EL
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Using Cisco DialOut for Telnet Connections
The Cisco DialOut feature enables users on a workstation operating Windows to send faxes or connect to service provider services outside the LAN by using modems attached or internal to a network access server. The Cisco DialOut feature extends the functionality of Telnet by enabling users to control the activity of these modems from their desktop computers using standard communications software.
The Cisco DialOut feature has two components:
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Both components are required and neither can function as a stand-alone feature.
The Telnet Extensions for Dialout component uses reverse Telnet to access modems attached to the network access server. This component enables the network access server to interface with the client/desktop component of the Cisco DialOut feature and to return Carrier Detect signals to the communications software so that the software can determine when to start dialing a particular number.
Telnet extensions allow the communications software running on the desktop computer of the client to control modem settings such as baud rate, parity, bit size, and stop bits.
To enable this feature, you only need to configure the access server or router for reverse Telnet and configure the appropriate lines to send and receive calls.
The client/desktop component of Cisco DialOut feature must be installed on the client workstation before this feature can be used. For information about installing and using the client/desktop component of the Cisco Dial-Out feature, and configuring the access server, see the DialOut Utility User Guide Cisco publication at Cisco.com.
Configuring Stream TCP
Stream TCP connections, or raw TCP or TCP-Clear connections as they are sometimes called, are used to transport a stream of 8-bit characters as-is over an IP network, between a TCP client and TCP server system. This method is used to transport legacy asynchronous application data through an IP network, for example, with a Point-of-Sale (PoS) terminal connecting to an application server.
To establish a Stream TCP connection from an EXEC session, use the /stream keyword with the telnet command. You will also generally want to configure the line to provide for data transparency. See the following procedure for the steps to do this.
Stream TCP Autocommand Procedure
In the following procedure, a line is configured so that any connection into it is automatically connected using Stream TCP to the application server at the specified IP address and TCP port (IP address 10.1.2.3 and TCP port 4321 in the examples).
Step 1
Router# configure terminalRouter(config)# line 33Router(config-line)# no motd-bannerRouter(config-line)# no exec-bannerRouter(config-line)# no vacant-messageRouter(config-line)# escape-character NONERouter(config-line)# no hold-characterStep 2
Router(config-line)# autocommand telnet 10.1.2.3 4321 /quiet /streamStep 3
Router(config-line)# autocommand-options telnet-faststream
Configuring LAT
The LAT protocol is the one used most often to connect to Digital hosts. LAT is a Digital-proprietary protocol. Cisco provides LAT technology licensed from Digital. This section describes how to configure the LAT transmission protocol.
The LAT protocol allows a user to establish a LAT connection to a host at another site, then pass the keystrokes from one system to the other. A user can establish a LAT connection through a router to a LAT host simply by entering the host name. The Cisco IOS software supports the LAT 5.2 specification.
LAT Overview
Unlike TCP/IP, LAT was designed to be used on LANs and it cannot be routed because it does not have a routing layer. However, a bridge or combined bridge and router, such as a Cisco router, can be used to carry LAT traffic across a WAN. Protocol translation can be used to carry LAT traffic over a WAN by first translating LAT to X.25 or Telnet, as shown in Figure 9.
Figure 9 Comparing LAT and TCP/IP Protocol Stacks
The following sections describe the Cisco implementation of LAT in more detail:
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LAT Functionality
The LAT protocol is asymmetrical; it has master and slave functionality. First, the LAT master starts a LAT circuit by sending a circuit start message, and then a LAT slave responds with its own circuit start message. From 1 to 255 LAT sessions can then be multiplexed on a circuit.
In a typical setup, where the terminal of the user is connected to a router, the router acts as the master, and the target VMS host acts as the slave.
For example, the following command results in the device named router1 acting as the master (or server) and the target VMS host named wheel acting as the slave (or host).
router1> lat wheelA router can also act as a slave when the user connects from one access server to another. For example, the following command results in router1 acting as the master (server) and router2 acting as the slave (host).
router1> lat router2In a LAT host-initiated connection, the VMS system always acts as the LAT slave. For example, a print job originating from a VMS system initiates or triggers the router to which the printer is connected to act as the LAT master. In short, the master-slave relationship also applies to host-initiated sessions from a LAT slave.
LAT Services
Resources such as modems, computers, and application software are viewed in a LAT network as services that any user in the network can use. A LAT node can offer one or more such LAT services, and more than one LAT node can offer the same LAT service.
A LAT node that offers one or more services, collectively called advertised services, broadcasts its services in the form of Ethernet multicast messages, called LAT service announcements. Conversely, a LAT node can listen for LAT service announcements on the network. These messages are cached in a dynamic table of known LAT services, collectively called learned services.
The Cisco IOS software supports both learned and advertised LAT services; therefore, it also supports incoming and outgoing LAT sessions. The services rating of its advertised nodes is determined dynamically but can also be set statically.
To establish outgoing connections to a LAT service, the Cisco IOS software searches for the service in the learned services cache. If one or more nodes is offering the same service, the node with the highest rating is chosen. For example, a LAT connection to a service offered by a VAX cluster connects to the node in that cluster with the smallest load and thus the highest service rating. These connections are how load balancing works in relation to a group of nodes offering the same service.
To establish an incoming connection, a LAT session connects from another LAT node to the service advertised by the local LAT node.
LAT Groups
Because any user can access any of the services on a LAT network, a LAT server manager uses the concept of group codes to allow or restrict access to the services.
When both the router and the LAT host share a common group code, a connection can be established between the two. If the default group codes have not been changed on either side, a user on any router can connect to any learned service on the network.
However, if you define groups for access servers or routers and LAT hosts, you can partition these services into logical subnetworks. You can organize the groups so that users on one device view one set of services, and users on another device (or another line on the same device) view a different set. You might also design a plan that correlates group numbers with organizational groups, such as departments. The section "LAT Configuration Task List" later in this chapter describes how to enter group code lists in your configuration file.
The services of a LAT host node cannot be accessed individually; access is granted, per node, on an
all-or-none basis.LAT Sessions and Connection Support
A LAT session is a two-way logical connection between a LAT service and the router. The connection is transparent to the user at a console connected to a LAT session; to the user it appears that connection has been made directly to the desired device or application program. There is no inherent upper limit to the number of LAT sessions you can create from an asynchronous terminal to the router.
A host print job connected to a router is called a host-initiated connection. The Cisco IOS software maintains a queue of hosts requesting connection by sending periodic status messages to the requesting host.
You can establish host-initiated connections by specifying a port number or by defining a service. These same services are used for connections from other access servers or routers.
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Connecting a VMS Host Using LAT
Connection to a VMS host is slightly different if you are connecting to a VMS host running VMS Version 5.4 or earlier than when connecting to a VMS host running VMS Version 5.5 or later software.
VMS Version 5.4 or Earlier System
If a host-initiated connection is received that specifies a destination port number that corresponds to a virtual port on the router, a virtual EXEC process will be created to allow the user to log in. This process can be used, in conjunction with the Digital set host/dte command on VMS, to connect to a router named router1 from a VMS host node, as shown in the following example:
$lcp :==$latcp$lcp create port lta300:$lcp set port lta300:/service=able /node=router1$set host/dte lta300:VMS Version 5.5 or Later System
To connect to a VMS host running VMS Version 5.5 or later software, you must turn on the outgoing connections of the VMS LAT hosts and use the Digital set host/lat command, as shown in the following example:
$lcp :== $latcp$lcp set node/connection =outgoing$set host/lat ablePort Names When Configuring a LAT Printer
When you configure a LAT printer, the LAT port name is the line number without a "TTY" designation on the show lines command output. For example, if you configure terminal line 10 (named ABLE) to be a LAT printer port, you must use the OpenVMS command to associate an arbitrary LAT device to the LAT port name, as follows:
$lcp :== $lcp$lcp create port lta300:$lcp set port/node=ABLE/port=10 lta300:The LAT port name is the line number without the "TTY," regardless of whether the format of the TTY line number is decimal or octal.
Additional LAT Capability
The Cisco IOS software fully supports the LAT protocol suite, and provides the following features:
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LAT Configuration Task List
The Cisco IOS software LAT protocol is supplied with a default configuration and does not require additional configuration for you to use it.
To enable LAT and customize LAT for your particular network environment, perform the tasks described in the following sections:
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The section "Monitoring and Maintaining LAT Connections" later in this chapter provides tips for maintaining LAT connections. The section "LAT Configuration and Connection Examples" later in this chapter provides LAT configuration examples.
Configuring Basic LAT Services
To enable basic LAT services, use the following commands beginning in interface configuration mode:
Use the lat out-group command to define the list of services to which a user can connect. You create this list by defining the group code lists used for connections from specific lines. You can limit the connection choices for an individual line by defining the group code lists for an outgoing connection. When a user initiates a connection with a LAT host, the line of the user must share a common group number with the remote LAT host before a connection can be made.
Use the lat group-list command to specify a name for group lists to simplify the task of entering individual group codes. A name makes it easier to refer to a long list of group code numbers. To display the defined groups, use the show lat groups command.
Use the lat service-group command to specify a group code mask to use when advertising all services for a node. You can enter more than one group code by listing the numbers. You can also enter both a group code name and group codes.
Use the lat remote-modification line configuration command to configure a LAT line so that a remote LAT node can change the operating characteristics of the line.
Enabling Inbound Services
Just as LAT services are offered by host computers, they also can be offered by access servers and routers, because they implement both the host and server portions of the LAT protocol. This capability allows connections from either hosts or local access servers or routers. A host connected to a local device is called a host-initiated connection.
The tasks described in this section define support for host-initiated connections. This support includes refining the list of services that the router will support. An incoming session can be to either a port or a service. The port name is the terminal line number, as reported by the show users all EXEC command.
To enable inbound services, use the following commands in global configuration mode as needed:
Use the show lat advertised EXEC command to display LAT services offered to other systems on the network.
A service must be specifically enabled, but not all of the attributes in the previous task table are necessary in a particular environment.
Controlling Service Announcements and Service Solicitation
You can configure the Cisco IOS software to support the service responder feature that is part of the LAT Version 5.2 specification.
Specifically, the DECserver90L+, which has less memory than other Digital servers, does not maintain a cache of learned services. Instead, the DECserver90L+ solicits information about services as they are needed.
LAT Version 5.2 nodes can respond for themselves, but LAT Version 5.1 nodes, for example, VMS Version 5.4 or earlier nodes, cannot. Instead, a LAT Version 5.2 node configured as a service responder can respond in proxy for those LAT Version 5.1 nodes.
The Cisco IOS software can be configured as a LAT service responder. Of course, if all your nodes are LAT Version 5.2 nodes, you need not enable the service responder features.
To control service announcements and service solicitations, use the following commands in global configuration mode:
Use the lat service-responder command to configure the Cisco IOS software to respond to solicit information requests addressed to LAT Version 5.1 nodes. This function allows nodes that do not cache service advertisements to interoperate with nodes that do not respond to solicit requests. Figure 10 shows how a router can act as a proxy for LAT servers.
Figure 10 Router as Proxy for LAT Server
The DECserver90L+ broadcasts a solicit information request in search of service for address Stella. The VMS host, Stella, is unable to respond to the request because it is running LAT Version 5.1. The access server is running LAT Version 5.2 with service responder enabled and informs the DECserver90L+ of the address for Stella.
Use the no lat service-announcements command to disable periodic broadcasts of service announcements. If service announcements are enabled, the LAT node will periodically broadcast service advertisements. If service announcements are disabled, the LAT node will not send service announcements, so a remote node requiring connection to the local node must use solicit-information messages to look up node information. Disable service announcements only if all of the nodes on the LAN support the service responder feature.
Use the lat service-timer command to adjust the time between LAT service advertisements for services offered. This command is useful in large networks with many LAT services and limited bandwidth.
Configuring Traffic Timers
You can customize the environment for sending LAT messages. The Cisco IOS implementation of LAT allows you to set the following features:
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These features affect all LAT connection types.
To enable these features, use the following commands in global configuration mode:
Optimizing Performance
To optimize performance for your LAT environment, use the following commands beginning in global configuration mode:
Use the lat host-buffers command to set the number of messages received by a host at one time. Increasing this number can enhance performance. Before LAT Version 5.2, LAT allowed only one outstanding message at one time on a virtual circuit. This restriction could limit the performance of the Cisco IOS software when it processed a large number of messages because only one Ethernet packet of data could be in transit at a time. During virtual circuit startup, each side communicates to the other how many outstanding messages it is willing to accept.
Use the lat server-buffers command to set the number of messages received by a server at one time. Increasing this number can enhance performance. Before LAT Version 5.2, LAT allowed only one outstanding message at one time on a virtual circuit. This restriction could limit the performance of Cisco IOS software when it processed a large number of messages because only one Ethernet packet of data could be in transit at a time. With LAT Version 5.2, nodes can indicate that they are willing to receive more than one message at a time. During virtual circuit startup, each side communicates to the other how many outstanding messages it is willing to accept.
Use the lat host-delay command to set a user-defined delay for the acknowledgment for incoming LAT slave connections. This command is useful in situations where you need to control the delay. For example, if data is being transferred between a Digital server (using LAT) and a UNIX host (using Telnet) via a protocol translator, the protocol translator imposes the LAT delay on the Telnet and the LAT service, where Telnet may time out due to the LAT restriction.
Defining LAT Access Lists
Because LAT groups were not intended to implement security or access control, the Cisco IOS software supports access lists to provide these functions. An access list is a sequential collection of permit and deny conditions that serve to restrict access to or from LAT nodes on a specific terminal line. Each access list statement defines a permit or deny condition and a matching criterion for the node name.
When a LAT connection is attempted (either incoming or outgoing), the node name of the destination service (not the service name) is compared against the regular expression. If they match, the connection is permitted or denied as specified.
To define access lists and conditions, use the following commands beginning in global configuration mode:
Enabling Remote LAT Modification
You can configure a LAT line so that a remote LAT node can change the operating characteristics of the line. To enable remote LAT modification, use the following command in line configuration mode:
Router(config-line)# lat remote-modification
Enables remote LAT modification of line characteristics.
Making LAT Connections
The LAT protocol is most often used to connect routers to Digital hosts. LAT is a Digital-proprietary protocol, and the Cisco IOS software uses LAT technology licensed from Digital to allow the following LAT services:
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For actual LAT connection examples, see the section "LAT Configuration and Connection Examples" later in this chapter.
To enable specific LAT connections or services, use the following commands in EXEC mode:
Step 1
Router> lat name [node node-name | port portname | /debug]
Connects to a LAT host.1
Step 2
Router> terminal lat out-group {groupname | number | range}
(Optional) Defines a temporary list of services to which you or another user can connect by defining the group code lists used for connections from specific lines.
Step 3
Router> show lat services [service-name]
(Optional) Lists available LAT services.
Step 4
Router> help
(Optional) Lists the subset of Digital commands that the Cisco IOS software supports.
1 You can quit the connection by pressing Ctrl-C or complete the connection by entering the password for a given service.
You can also set your preferred connection protocol to any available connection protocol supported in the Cisco IOS software. Your preferred connection protocol is also referred to in the Cisco IOS software as a "preferred transport type." If your preferred connection protocol is set to lat, you can use the connect command in place of the lat command. To configure a preferred connection protocol, use the transport preferred command. When your preferred connection protocol is set to none or to another protocol, you must use the lat command to connect to a LAT host.
To specify a temporary list of services to which you or another user can connect, you must define the group code lists used for connections from specific lines. You limit the connection choices for an individual line by defining the group code lists for an outgoing connection. To define a group code list, use the terminal lat out-group command. When a user initiates a connection with a LAT host, the line of the user must share a common group number with the remote LAT host before a connection can be made. The group code range must be a subset of the configured group code range of the line.
You can have several concurrent LAT sessions open and switch between them. To open a subsequent session, first enter the escape sequence (Ctrl-Shift-6 then x [Ctrl^x] by default) to suspend the current session. Then open a new session. To list the available LAT services, enter the show lat services EXEC command.
When you are done with the LAT session, use the exit command to end it, then terminate the active LAT session by entering the Ctrl-C key sequence.
Monitoring and Maintaining LAT Connections
To monitor and maintain LAT connections, use the following commands in EXEC mode as needed:
